2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
TimeTable
Fri (Feb. 21)
Sat (Feb. 22)
Opening Ceremony
Chair: Je-Geun
Park
08:50-09:00
YK Bang/ J Yu
Sun (Feb. 23)
Mon (Feb. 24)
Tue (Feb. 25)
Wed (Feb. 26)
Session #1:
Session #4
Session #7
Session #8
Session #11
Chair: Je-Geun Park
Chair: Jaejun Yu
Chair: J. Gardner
Chair: J. Goff
Chair: A. Chernyshev
Electronic Structure I Electronic Structure II Exotic Ground States I Exotic Ground States II Quantum Magnetism II
15:00-18:00
Registration
at Ensemble
Hall
18:00-20:00
Welcome
Party
Venue: Hotel
Tirol B1
09:00-09:40
Shik Shin
09:00-09:40
Atsushi Fujimori
09:00-10:00
Hide Takagi
09:00-10:00
Maxim Mostovoy
09:00-10:00
A. Tennant
09:40-:10:20
Jaehoon Park
09:40-:10:20
Changyoung Kim
10:20-10:40
Break
10:20-10:40
Break
10:00-10:20
Break
10:00-10:20
Break
10:00-10:20
Break
10:40-11:20
Chun-Fu Chang
10:40-11:20
Di-Jing Huang
10:20-11:00
Yong-il Shin
10:20-11:00
Ki-Seok Kim
10:20-11:00
Y. Lee
11:20-12:00
Shigemasa Suga
11:20-12:00
Tsuyoshi Kimura
11:00-11:40
C. Hicks
11:00-11:40
Ke He
11:00-11:40
Ch. Ruegg
Session #2
Chair: D. J. Huang
Interface Physics
Session #5
Chair: H. Takagi
New Materials II
Session #9
Chair: A. Tennant
Quantum Magnetism I
Session #12
Chair: Yunkyu Bang
Exotic Ground States
III
13:30-14:10
Jaejun Yu
13:30-14:10
Jason Gardner
13:30-14:30
A. Chernyshev
13:30-14:30
T. Ziman
14:10-14:50
Ya-Ping Chiu
14:10-14:50
Myung Joon Han
14:50-15:10
Break
14:50-15:10
Break
14:30-14:50
Break
14:30-14:50
Break
15:10-15:50
Woo Seok Choi
15:10-15:50
Minoru Nohara
14:50-15:30
M. D. Le
14:50-15:30
Cheol Hwan Park
15:50-16:30
Ying Hao Chu
15:50-16:30
Kee Hoon Kim
15:30-16:10
J. Goff
15:30-16:10
P. Armitage
16:30-17:00
Break
16:30-17:00
Break
16:10-16:30
Break
16:10-16:30
Closing Ceremony
Session #3
Chair: T. Kimura
New Materials I
Session #6
Chair: A. Fujimori
New Materials III
Session #10
Chair: Tae Won Noh
New Materials IV
17:00-17:40
Hiroshi Eisaki
17:00-17:40
Kookrin Char
16:30-17:30
A. Bostwick
17:40-18:20
Ping-Hui Lin
17:40-18:20
Takuro Katsufuji
17:30-18:10
Hosub Jin
Free Discussion /
Excursion (4
hours hiking
program at
Deogyusan
National Park in
preparation )
18:30 - 20:00
Poster Session
(Snack and light
beverage will be
provided)
Venue: Symphony
Hall
18:30 - 21:00
Banquet
Venue: Symphony
Hall
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2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
Chairs&Titles
Saturday, Fab. 22:
Session #1: Electronic Structure I (Chair: Je-Geun Park)
(O1) Shik Shin
Ultra-high resolution laser-ARPES Study on high Tc-Superconductors
(O2) Jaehoon Park
Exotic Ordering Behaviors in Metallic IrTe2
(O3) Chun-Fu Chang
Soft x-ray absorption and diffraction on strongly correlated oxides
(O4) Shigemasa Suga
New era of photoelectron spectroscopy: complete 3D spin-polarized angle-resolved
photoelectron spectroscopy by spin-polarized momentum-microscope
Session #2: Interface Physics (Chair: D. J. Huang)
(O5) Jaejun Yu
Origin of Two-Dimensional Electron Gas at LaAlO3/SrTiO3 Interface and SrTiO3 Surface
(O6) Ya-Ping Chiu
Atomic-Scale Interfacial Electronic Structures across Hetero-Interfaces in Complex Oxides
(O7) Woo Seok Choi
Controlling characteristics of 2 dimensionally confined electrons in perovskite oxide
heterostructures
(O8) Ying Hao Chu
The coupling of strongly correlated electron systems and multiferroic periodic domain
patterns
Session #3: New Materials I (Chair: T. Kimura)
(O9) Hiroshi Eisaki
Magnetism and superconductivity in the three-dimensional electronic structures of Fe
pnictides
(O10) Ping-Hui Lin
Electronic Structure Evolution and the Metallic Behavior of FeTe Through the Magnetic
transition
Sunday, Feb. 23:
Session #4: Electronic Structure II (Chair: Jaejun Yu)
(O11) Atsushi Fujimori
Photoinduced dynamics of spinel MnV2O4 as a spin-orbital coupled system
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2014 Quantum Materials Symposium
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(O12) Changyoung Kim
Orbital angular momentum driven spin Hall effect
(O13) Di-Jing Huang
High-resolution RIXS for studying low-energy excitations of transition-metal compounds
(O14) Tsuyoshi Kimura
Study of helix-chirality in spin and quadrupole orientations by resonant x-ray scattering
Session #5: New Materials II (Chair: H. Takagi)
(O15) Jason Gardner
Spin Correlations in Tb2Ti2O7 and Tb2Sn2O7
(O16) Myung Joon Han
Electronic structure, superconductivity, and ferromagnetism in nickelate superlattices
(O17) Minoru Nohara
Superconductivity at 45 K in CaFeAs2 and CaFe2As2 with La doping
(O18) Kee Hoon Kim
Manifestation of magnetic quantum fluctuations in the dielectric properties
Session #6: New Materials III (Chair: A. Fujimori)
(O19) Kookrin Char
High mobility, stability, and bipolar dopability of transparent perovskite semiconductor
BaSnO3
(O20) Takuro Katsufuji
Photoinduced dynamics of spinel MnV2O4 as a spin-orbital coupled system
Monday, Feb. 24:
Session #7: Exotic Ground States I (Chair: J. Gardner)
(O21) Hide Takagi
Exotic electronic phases derived from semi-metals+
(O22) Yong-il Shin
Geometric Hall Effect in a Spinor Bose-Einstein Condensate
with a Skyrmion Spin Texture
(O23) C. Hicks
Strong increase of Tc of Sr2RuO4 under both tensile and compressive strain
Tuesday, Feb. 25:
Session #8: Exotic Ground States II (Chair: J. Goff)
(O24) Maxim Mostovoy
Skyrmionics
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2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
(O25) Ki-Seok Kim
Electric-field control of ferromagnetic moment in rare-earth orthoferrite
(O26) Ke He
Quantum anomalous Hall effect in magnetically doped topological insulator
Session #9: Quantum Magnetism I (Chair: A. Tennant)
(O27) A. Chernyshev
Odd interactions in quantum magnets and liquids
(O28) M. D. Le
Observation of magnon decay and non-linear spin waves in LuMnO3
(O29) J. Goff
Defects in spin ice
Session #10: New Materials IV (Chair: Tae Won Noh)
(O30) A. Bostwick
Many Body Physics in Graphene with ARPES
(O31) Hosub Jin
Spin-orbital entangled jeff states in 4d and 5d transition metal systems
Friday, Feb. 26:
Session #11: Quantum Magnetism II (Chair: A. Chernyshev)
(O32) A. Tennant
TBA
(O33) Y. Lee
Neutron scattering studies of the kagomé lattice: quantum spin liquids and topological
magnon bands
(O34) Ch. Ruegg
Quantum and thermal criticality in magnets
Session #12: Exotic Ground States III (Chair: Yunkyu Bang)
(O35) T. Ziman
Correlation effects in skew scattering mechanisms of Anomalous and Spin Hall Effects
(O36) Cheol Hwan Park
Quasiparticle carrier dynamics in graphene from first principles
(O37) P. Armitage
Recent Thz results on quantum correlated matter
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2014 Quantum Materials Symposium
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Abstracts
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2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
[O1] Ultra-high resolution laser-ARPES Study on high Tc-Superconductors
Shik Shin
Institute for Solid State Physics (ISSP), University of Tokyo
Angle resolved photoemission spectroscopy (ARPES) is very powerful to know the solid state
properties, because we can know the solid state electrons directly. We have developed lowtemperature high-resolution laser-based ARPES system and recently achieved the highest
energy resolution of ~ 100 μeV and the lowest sample temperature of ~ 1.0 K. We confirmed
the performance of the laser-ARPES apparatus by the measurement of the superconducting
gaps of the several low-Tc elemental superconductors (Re: Tc=1.7 K, Al: Tc=1.2 K). Laser
ARPES is found to be very useful for the superconductors, strongly-correlated materials, and
heavy Fermion materials, organic materials.
We would like to show our recent results of superconducting-gap measurements on Bi2212 by
laser-ARPES. Identifying temperature dependence of the pairing gap in cuprates is essential
to formulate the mechanism of high temperature superconductivity. The pairing gap,
observed near the nodal, was previously proposed to be rather conventional, closing at the
superconducting transition temperature (Tc) with the BCS temperature dependence. By using
a laser-ARPES spectroscopy with an ultra-high energy resolution , we reveal that the d-wave
gap with a point node, in fact, persists up to far above Tc (Tpair~1.5Tc) in the optimally doped
Bi2212.
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[O2] Exotic Ordering Behaviors in Metallic IrTe2
K.-T. Ko1,2,3, H.-H. Lee1,2,3, D.-H. Kim1,2,3, J.-J. Yang2,4, T. A. Tyson5, S-W. Cheong2,4,5, R.
Gammag3, K.-S. Kim3, H.-S. Kim3,6, T.-H. Kim3,6, H.-W. Yeom3,6, J. S. Kim3, T.-Y. Koo7,
H.-D. Kim7 , and J.-H. Park1,2,3
1
Center for Cross-coupled Complex Materials Research, POSTECH, Pohang 790-784, Korea
2
Max Plank POSTECH Center for Complex Materials Research, POSTECH, Pohang 790784, Korea
3
Department of Physics, POSTECH, Pohang 790-784, Korea
4
Lab. for Pohang Emergent Materials & Department of Physics, POSTECH, Pohang 790784, Korea
5
Rutgers Center for Emergent Materials and Department of Physics & Astronomy, Rutgers
University, Piscataway New Jersey 08854, USA
6
Center for Low Dimensional Electronic Systems, Institute for Basic Science (IBS),
POSTECH, Pohang 790-784, Korea
7
Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Korea
The strong spin-orbit coupling has become a key issue in the condensed matter physics in the
last decade since discovery of its related emerging phenomena such as multiferroicity,
topological insulator, noble Jeff = 1/2 Mott state. Recently, the 5d transition metal compound
IrTe2 system has been reported to exhibit an exotic charge density wave (CDW) behavior.
Furthermore, the system also exhibits superconductivity with suppression of CDW by Pt or Pd
doping on the Ir sites. Differently from the 3d electrons, which show strong localized characters
governed by the on-site Coulomb repulsion U, the 5d electrons have been widely considered as
band-like itinerant electrons since their on-site U is much reduced and the band width W largely
increases. On the other hand, the relativistic spin-orbit coupling energy, which is small to be
treated as a perturbation term in the 3d transition metal, becomes so large that it can completely
disturb the electronic structure in the 5d system. Here we discuss the exotic ordering behaviours
in IrTe2 based on comprehensive studies of the macrsoscopic transport data, the microscopic
synchrotron based spectroscopic and scattering results, and Atomic scale scanning tunnelling
microscope results.
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2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
[O3] Soft x-ray absorption and diffraction on strongly correlated oxides
Chun-Fu Chang
Max Planck Institute for Chemical Physics of Solids
Noethnitzer Strasse 40, 01187 Dresden, Germany
Rich physical properties of correlated materials originate from the cooperative behaviors of
charge, spin, orbital as well as their couplings to the lattice. Indeed, this electronic complexity
has been regarded as a crucial role to understand many epochal phenomena such as
superconductivity, colossal magnetoresistance, multiferroics, metal-insulator transition and so
on. Over the last few decades, both experimental and theoretical developments have been
progressive, however still there are many underlying mechanisms far from clear. A direct
probing of charge, spin, and orbital states in these systems can be of great help to unravel the
underlying physics of these novel phenomena.
The well-developed soft x-ray absorption spectroscopy (XAS) is extremely sensitive to the local
electronic structure, i.e., charge, spin, and orbital states of the ground state. Sharing the same
optical transitions, resonant soft x-ray diffraction (RSXD) delivers the ordered (structureselective) information. In this talk we will present our studies on La1.5Sr0.5CoO4 and Fe3O4 by
means of these two spectroscopic methods.
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2014 Quantum Materials Symposium
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[O4] New era of photoelectron spectroscopy: complete 3D spin-polarized
angle-resolved photoelectron spectroscopy by spin-polarized momentummicroscope
S.Suga
Institute of Scientific & Industrial Research, Osaka University
8-1 Mihogaoka, Ibaraki, Osaka 567-0047
Angle resolved and spin polarized photoelectron spectroscopy is a powerful means to study
electronic structures of various solids ranging from magnetic materials to non-magnetic
materials owing to the dipole selection rules with polarized light excitation. The low efficiency
of spin-detectors, however, strongly limited its application to wide variety of materials up to
now.
Recent development of higher efficiency spin detectors such as Fe-O as well as two dimensional
spin detectors as W and Ir-Au has overcome the strong limitation of spin-polarized angle
resolved photoelectron spectroscopy (SP-ARPES) in very recent years. In addition, the
development of a momentum microscope composed of a PEEM entrance lens and a tandem
double hemispherical electron energy analyzers has facilitated two dimensional ARPES with
simultaneous kx,ky measurement by a two dimensional detector in the form of EB(kx,ky). By
inserting a two dimensional spin-detector after the tandem hemispherical analyzer, one can
measure the spin polarization of photoelectrons in the form of P(EB(kx,ky)). The efficiency of
the SP-ARPES is upgraded by more than 10,000 times than that of traditional SP-ARPES and
now full set of information on electronic structures is easily available.
History as well as the present status of multi-dimensional SP-ARPES is discussed in this
presentation.
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2014 Quantum Materials Symposium
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[O5] Origin of Two-Dimensional Electron Gas at LaAlO3/SrTiO3 Interface
and SrTiO3 Surface
Jaejun Yu
Department of Physics and Astronomy, Seoul National University
Recently the interface of two insulating LaAlO3 (LAO) and SrTiO3 (STO) oxides was
discovered to be metallic and further reported to exhibit magnetism as well as superconductivity.
While two dimensional electron gas at the n-type LAO/STO interface was suggested to arise
from a so-called ‘polar catastrophe’ concept, which is based on a simple idea of electrostatic
breakdown of a polar insulating interface consisting of ionic charges, the origin of a twodimensional electron gas (2DEG) at the LAO/STO interface remains unclear despite the
enormous activities on this system. In this talk we propose a phenomenological model for
understanding electronic and redox screening at the surface and interface of oxide heterostructures based on first-principles calculation results.
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2014 Quantum Materials Symposium
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[O6] Atomic-Scale Interfacial Electronic Structures across HeteroInterfaces in Complex Oxides
Ya-Ping Chiu
Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
Interfaces have gotten a lot of attention recently and provide a powerful route to create and
manipulate the charge, spin, orbital, and lattice degrees of freedom. Motivated by the
importance of the critical nanoscale interfacial science that governs the applications of devices,
the objective of our studies is emphasized the interfacial characteristics of hetero-epitaxial
structures, and elucidated the fundamental mechanisms that pertain in these systems.
In our studies, cross-sectional scanning tunneling microscopy is employed to observe directly
the epitaxial interfacial structures and the local electronic properties with atomic-level insight.
Our scanning tunneling microscopy and spectroscopy studies with atomic precision provide
direct experimental insight into the origin and the natural evolution of the electronic properties
across heterointerfaces in complex oxides, which provide a lot of insights to this community.
Selected references:
1. Min-Chuan Shih, Bo-Chao Huang, Chih-Cheng Lin, Shao-Sian Li, Hsin-An Chen, Ya-Ping
Chiu*, Chun-Wei Chen*, “Atomic-Scale Interfacial Band Mapping across Vertically PhasedSeparated Polymer/Fullerene Hybrid Solar Cells”, Nano Letters, 13, 2387 (2013).
2. Bo-Chao Huang, Ya-Ping Chiu*, Po-Cheng Huang, Wen-Ching Wang, Vu Thanh Tra, Jan-Chi
Yang, Qing He, Jiunn-Yuan Lin, Chia-Seng Chang, Ying-Hao Chu, “Mapping Band Alignment
across Complex Oxide Heterointerfaces”, Phys. Rev. Lett., 109, 246807 (2012).
3. Ya-Ping Chiu*, Yu-Ting Chen, Bo-Chao Huang, Min-Chuan Shih, Jan-Chi Yang, Qing He,
Chen-Wei Liang, Jan Seidel, Yi-Chun Chen, Ramamoorthy Ramesh, Ying-Hao Chu, “Atomicscale evolution of local electronic structure across multiferroic domain walls”, Adv. Mater., 23,
1530 (2011).
4. B. C. Huang, Y. T. Chen, Y. P. Chiu*, Y. C. Huang, J. C. Yang, Y. C. Chen, Y. H. Chu, “Direct
observation of ferroelectric polarization-modulated band bending at oxide interfaces”, Appl. Phys.
Lett. 100, 122903 (2012).
5. Y. P. Chiu*, B. C. Huang , M. C. Shih, J. Y. Shen, P. Chang, C. S. Chang, M. L. Huang, M. -H.
Tsai, M. Hong*, and J. Kwo*, “Atomic-scale Determination of Band Offsets at the Gd2O3/GaAs
(100) Hetero-interface Using Scanning Tunneling Spectroscopy”, Appl. Phys. Lett. 99, 212101
(2011).
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[O7] Controlling characteristics of 2 dimensionally confined electrons in
perovskite oxide heterostructures
Woo Seok Choi
Department of Physics, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Korea
Transition metal oxides exhibit vastly diverse physical properties based on strong correlation
between the transition metal electrons and oxygen ions. Among the emergent phenomena,
electron gas formed at the interface between two perovskite oxides has attracted tremendous
recent attention due to its intriguing physics and possibility for novel device applications.
LaTiO3/SrTiO3 (LTO/STO) heterostructure is one of the prominent examples which exhibit
such intriguing 2D conduction, even though the constituents are normally insulating. More
interestingly, the bulk counterpart, LaxSr1-xTiO3 (LSTO) exhibits a filling-controlled insulatormetal transition (IMT).
In this study, we investigated the filling controlled IMT in 2 dimension by fabricating
fractionally δ-doped LSTO/STO superlattices (SLs), in order to understand and control the
charge carrier characteristics. Fractional layers of LSTO have been grown in between STO
layers using advanced pulsed laser epitaxy. It is found that the transport properties are governed
by a multichannel conduction with at least two distinctly different carriers: (1) High-densitylow-mobility carriers presenting at the LSTO layer and (2) low-density-high-mobility carriers
residing in the STO layers, spatially away from the δ-doped layer. By optimizing x, we could
tune the effective mass and carrier density to enhance the carrier mobility by about an order of
magnitude, selectively for the high-density-low-mobility carriers. This suggests that the
fractional δ-doping is an effective way to controlling the properties of charge carriers in oxide
2DEGs.
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2014 Quantum Materials Symposium
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[O8] The coupling of strongly correlated electron systems and
multiferroic periodic domain patterns
Ying-Hao Chu1,2
1
Department of Materials Science & Enginnering, National Chiao-Tung University,
Hsinchu 30010, Taiwan
2
Institutes of Physics, Academia Sinica, Taipei 100, Taiwan
Strongly correlated electron systems have drawn lots of attentions due to the interactions
between order parameters—spin, charge, lattice, and/or orbital. These interactions cause
intriguing phenomena, such as high temperature superconductivity, multiferroics, colossal
magneto-resistance, and then offer crucial opportunities for developing new electronic
devices. In this talk, we propose a novel process to manipulate the entanglement of these
systems by fabricating heteroepitaxial structures composing of strongly correlated electron
systems with periodic BiFeO3 domain structure. The periodic domain structures of BiFeO3
are electrically controllable and provide a variety of strain modulation, electrostatic
modification, and magnetic interaction to interact with order parameters in strongly
correlated electron systems. Our results show strongly anisotropic transport behaviors
captured by different temperatures of metal-insulator transition and superconducting
transition, which are potentially electrically controllable. The coupling behaviors between
periodic domain and strongly correlated systems are explored based on various techniques.
The combinations of these materials would offer the insights of the interplays between order
parameters as well as new solutions to next-generation electronic devices.
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2014 Quantum Materials Symposium
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[O9] Utilizing high-pressure techniques for developing new
superconductors / elevating superconducting transition temperatures
Hiroshi Eisaki, Akira Iyo, Nao Takeshita, Hijiri Kito, Shigeyuki Ishida
National Institute of Advanced Industrial Science and Technology (AIST)
Throughout the history of high transition temperature (high-Tc) superconductivity, highpressure (HP) technique has been playing significant roles. Sample synthesis under HP
conditions (typically several GPa) turned out to be more advantageous compared to the
conventional ambient pressure methods in many respects, such as the controlled modification
of the phase diagram, enhanced reactivity, and prevention of the evaporation, etc. Using HP
synthesis technique, various cuprates and iron-based high-Tc superconductors have been
discovered so far. It is also well recognized that the application of HP on the synthesized
samples results in changing their structural parameters (bond length, bond angle, etc.) which
determine their physical properties (density of states, phonon frequencies, magnetic coupling
energy, etc.,) thus dramatically affects their superconducting properties.
In this presentation, we will report on our recent trials in sample synthesis/physical properties
measurements using HP techniques, which include the discovery of several superconductors
and the successful observation of zero-resistivity above 150K in the mercury-based cuprate
superconductors.
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2014 Quantum Materials Symposium
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[O10] Electronic Structure Evolution and the Metallic Behavior of FeTe
Through the Magnetic transition
Ping-Hui Lin
Institute of Physics, Academia Sinica, Taiwan
phlinjoy@phys.sinica.edu.tw
We investigate with angle-resolved photoelectron spectroscopy (ARPES) the changes of the
Fermi surface and the main bands from the paramagnetic state to the antiferromagnetic state.
By combining ARPES measurements in different experimental geometric configurations, we
have isolated the main bands of in the iron-based superconductors and studied their evolution
through the magnetic or superconducting transitions. Our observations correlate well with the
changes observed in transport measurements occurring below 72 K in FeTe.
Previous ARPES results have presented several similarities in the electronic structure of ironbased systems, whereas the hole-like and electron-like states near the EF have Fe 3d character.
Despite these similarities, the actual magnetic structures are different for the magnetic ironchalcogenide and iron-pnictide systems. In the pnictides, spins align in stripes with the wave
vector along (π, π) direction. In FeTe, the magnetic ordering exhibits a double stripe magnetic
order with the associating wave vector, QAFM =(π, 0), rotated by 45° with respect to the one
of iron-pnictide. Consequently, the evolution of FeTe through the magnetic transition is
completely different from that observed in Fe pnictides, as nesting is absent.
The AFM state of FeTe is a rather good metal, in agreement with our magnetic band structure
calculation. On the other hand, the anomalous FeTe electronic structure at the paramagnetic
state deviates strongly from the band calculation, with a large pseudogap of 65 meV on the
electron pocket that closes in the AFM state. In this talk I will discuss this behavior in
connection with spin fluctuations existing above the magnetic transition and the correlations
predicted in the spin-freezing regime of the incoherent metallic state.
Reference:
1. P.-H. Lin, Y. Texier, A. Taleb-Ibrahimi, P. Lefevre, F. Bertran and V. Brouet, Phys. Rev. Lett,
111, 217002 (2013)
2. V. Brouet, M. Fuglsang Jensen, P.-H. Lin, A. Taleb-Ibrahimi, P. Le fevre, F. Bertran, C.-H. Lin,
W. Ku, A. Forget, and D. Colson, Phys. Rev. B, 86, 075123 (2012)
3. M. Fuglsang Jensen, V. Brouet, E. Papalazarou, A. Nicolaou, A. Taleb-Ibrahimi, P. Le fevre, F.
Bertran, A. Forget, and D. Colson, Phys. Rev. B, 84, 014509 (2011)
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[O11] Magnetism and superconductivity in the three-dimensional
electronic structures of Fe pnictides
Atsushi Fujimori
Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033
Interplay between magnetism, structural distortion, and superconductivity is the essential
characteristic of Fe-based superconductors. However, fundamental issues such as whether the
magneto-structural phase transition is driven by Fermi-surface (FS) nesting or local magnetic
interaction and how important the FS nesting is for superconductivity have remained unsettled.
To resolve these issues, studies on systems with different c-axis parameters will give useful
insight since the three-dimensionality of FSs and magnetic interaction between neighboring
FeAs layers should sensitively depend on the distance between the layers.
We have studied the FSs, band dispersions, and superconducting gaps of the BaFe2(As,P)2 [1,2]
and SrFe2(As,P)2 systems using ARPES and DFT calculations. The TN of the parent compound
as well as the Tc of the optimally doped compound are higher in the SrFe2(As,P)2 system than
BaFe2(As,P)2 [3]. Hole FSs are found to be more strongly warped in SrFe2(As,P)2, suggesting
that the magnetic ordering is driven by local magnetic interaction including interlayer one. Mass
renormalization is found to be stronger in SrFe2(As,P)2, consistent with the stronger magnetism.
The superconducting gap is more anisotropic for the electron and hole FSs in BaFe2(As,P)2 [1]
and SrFe2(As,P)2, respectively, that is, gap anisotropy and FS warping seem correlated.
This work has been done in collaboration with H. Suzuki, S. Ideta, T. Yoshida, K. Okazaki, T.
Shimojima, Y. Ohta, S. Shin, M. Hashimoto, D. Lu，Z.-X. Shen，H. Anzai, A. Ino, M. Arita,
H. Namatame, M. Taniguchi, H. Kumigashira, K. Ono, T. Kobayashi, S. Miyasaka, S. Tajima,
S. Kasahara, T. Terashima, T. Shibauchi, Y. Matsuda, M. Nakajima, Y. Tomioka, T. Itoh, K.
Kiho, C.-H. Lee, A. Iyo, H. Eisaki, and S. Uchida.
Reference:
[1] T. Yoshida et al., Phys. Rev. Lett. 106, 117001 (2011)
[2] T. Yoshida et al., arXiv:1301.4818.
[3] T. Kobayashi et al., Phys. Rev. B 87, 174520 (2013)
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[O12] Orbital angular momentum driven spin Hall effect
Changyoung Kim
Department of Physics, Yonsei University, Seoul, Korea
Orbital angular momentum (OAM), usually ignored in solids (OAM quenching), is found to
play an important role in the electronic structure for a broad range of materials. In our previous
work on the Rashba effect,[1,2] we obtained a new effective Hamiltonian that incorporates the
role of OAM and explains many aspects of the Rashba effect.
We apply the effective Hamiltonian to the problem of spin Hall effect (SHE). The key aspect
of our interpretation is that the driving force comes from the OAM, caused by the coupling the
applied electric field and asymmetric charge distribution described by the new effective
Hamiltonian. SHE then comes as a side effect through the spin-orbit coupling. An important
result of this view is that the Rashba and SHE are driven by the same microscopic mechanism.
The proposed model can quantitatively predict the magnitude of SHE and account for the
material dependent sign reversal of spin Hall current , .
Reference:
[1] S. R. Park, Phys. Rev. Lett.,108, 046805 (2012)
[2] S. R. Park, Phys. Rev. Lett.,107, 0156803 (2011)
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[O13] High-resolution RIXS for studying low-energy excitations of
transition-metal compounds
Di-Jing Huang
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
Complex materials such as transition-metal oxides exhibit various intriguing phenomena,
including high-temperature superconductivity, metal-insulator transition, and multiferroicity.
Recent developments of material synthesis and spectroscopic techniques in the soft x-ray
regime provide us great opportunities to unravel interesting phenomena of these novel
materials.
In this talk, we will present our recent development on resonant inelastic soft X-ray scattering
(RIXS) spectroscopy to study low-energy excitations of transition-metal compounds. The
design of the monochromator and spectrometer is based on the energy-compensation principle
of grating dispersion which greatly enhances the efficiency of measurement of inelastic soft
X-rays scattering. Test measurements of this new system will be discussed, including spinflip, d-d and charge-transfer excitations of NiO and Fe3O4
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[O14] Study of helix-chirality in spin and quadrupole orientations by
resonant x-ray scattering
T. Kimura1, Y. Tanaka2, Y. Hirakaoka1, T. Usui1, H. Nakajima1, M. Taguchi2, A. Chainani2,
M. Oura2, S. Shin2,3, and Y. Wakabayashi1
1
Graduate School of Engineering Science, Osaka University
2
RIKEN SPring-8 Center
3
ISSP, University of Tokyo
Resonant x-ray scattering is known as powerful technique to study symmetry breakings by
orderings of various multipole moments, such as spin and orbital. This technique is recently
applied to verify symmetry breakings by the development of the chirality which is determined
as an asymmetry of the object upon its mirroring in crystallography and magnetism, and which
plays a crucial role in various materials’ functionality such as piezoelectricity and
multiferroicity. With the help of the resonant x-ray scattering technique using circularlypolarized and highly-focused x-ray beam, we investigated the helix-chiral domains of magnetic
dipole and electric quadrupole moments in magnetoelectric-related systems with right-handed
and left-handed helical structures.
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[O15] Spin Correlations in Tb2Ti2O7 and Tb2Sn2O7
J. S. Gardner1, G. Ehlers2, B. D. Gaulin3
1
2
Neutron Group, NSRRC, Hsinchu, 30076, Taiwan
SNS Project, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
3
Dept. of Physics, McMaster University, Hamilton LS8 $M1, Canada
At first glance Tb2Ti2O7 and Tb2Sn2O7 should have very similar ground states. The Tb3+ ion
is the only magnetic species in the system and it makes up a sublattice of corner sharing
tetrahedral. The Ising property of the spins and the antiferromagnetic coupling between them
makes this system susceptible to geometric frustration. In fact, the Curie-Weiss constant for
both compounds is approximately 15 K. However, no frozen state, either long range or short
range has been observed in Tb2Ti2O7 whilst Tb2Sn2O7 enters a partially ordered state at ~0.9
K. I will report on recent neutron scattering data that reveals the differences between these two
compounds.
Reference:
[1] J. S. Gardner, et al., Phys. Rev Lett., 82, 1012 (1999).
[2] I. Mirebeau, et al., Phys. Rev Lett., 94, 246402 (2005).
[3] B. D. Gaulin et al., Phys. Rev. B 84, 140402 (2011)
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[O16] Electronic structure, superconductivity, and ferromagnetism in
nickelate superlattices
Myung Joon Han
Department of Physics, Korea Advanced Institute of Science and Technology
mj.han@kaist.ac.kr
Our recent calculation results on two different nickelate superlattice systems will be presented;
LaNiO3/LaAlO3 (or its variant) and LaNiO3/LaMnO3. For the former, the possibility of the
cuprate-like superconductivity has been actively debated. Contrary to the previous theoretical
suggestion, our DMFT (dynamical mean-field theory) and GW calculations do not support the
one-band physics and high-temperature superconductivity in this type of heterostructure [1-3].
I will discuss the possible direction to search for those properties. For the latter, recent
experiments report the ferromagnetism and exchange bias while the origin of them still remains
unclear. Our first-principles calculation provides a clear understanding of this phenomenon; the
charge transfer from Mn to Ni plays a crucial role in combination with the confinement effect
[4].
Reference:
[1] M. J. Han et al., Phys. Rev. Lett. 107, 206804 (2011)
[2] M. J. Han and T. Kotani (in preparation)
[3] H. -S. Kim and M. J. Han, arxiv:1306.0713 (submitted)
[4] A. T. Lee and M. J. Han, Phys. Rev. B 88, 035126 (2013)
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[O17] Superconductivity at 45 K in CaFeAs2 and CaFe2As2 with La doping
M. Nohara
Department of Physics, Okayama University, Japan
We discovered superconductivity in novel 112-type (Ca1-xLax)FeAs2 [1]. The compound
crystallizes in a monoclinic structure (space group P21), in which FeAs layers alternate with
CaAs spacer layers such that monovalent arsenic forms zigzag chains. Superconductivity at 34
K was observed for the x = 0.1 sample, while trace superconductivity was observed at 45 K for
the x = 0.21 sample, demonstrating the potential of the 112-phase for higher transition
temperature.
Another way to realize higher Tc is co-doping of lanthanum and phosphorus in 122-type
CaFe2As2, which results in superconductivity at 45 K [2]. Superconductivity with a substantial
shielding volume fraction was observed at 0.12 ≤ x ≤ 0.18 and y = 0.06 in Ca1-xLaxFe2(As1-yPy)2.
In this doping range, the system exhibits crossover of the lattice collapse transition, which is
characterized by the formation of As2 dimers between the adjacent FeAs layers.
Reference:
[1] N. Katayama, K. Kudo, S. Onari, T. Mizukami, K. Sugawara, Y. Sugiyama, Y. Kitahama, K. Iba,
K. Fujimura, N. Nishimoto, M. Nohara, and H. Sawa, J. Phys. Soc. Jpn. 82, 123702 (2013).
[2] K. Kudo, K. Iba, M. Takasuga, Y. Kitahama, J. Matsumura, M. Danura, Y. Nogami, and M.
Nohara, Sci. Rep. 3, 1473 (2013).
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[O18] Manifestation of magnetic quantum fluctuations in the dielectric
properties
Jae Wook Kim1, Seunghyun Khim1, Sae Hwan Chun1, Y. Jo2, L. Balicas2, H. T. Yi3, S.-W.
Cheong3, N. Harrison4, C. D. Batista5, Jung Hoon Han6 and Kee Hoon Kim1
1
CeNSCMR, Department of Physics and Astronomy, Seoul National University, Seoul 151747, Republic of Korea
2
National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL 32310, USA
3
Rutgers Center for Emergent Materials and Department of Physics and Astronomy,
Piscataway, NJ 08854, USA
4
NHMFL and Materials Physics and Applications - Condensed Matter and Magnetic Science
(MPA-CMMS), Los Alamos National Laboratory (LANL), Los Alamos, NM 87545, USA
5
Theoretical Division, T-4 and Center for Nonlinear Studies, LANL, Los Alamos, NM 87545,
USA
6
Department of Physics, Sungkyunkwan University, Suwon 440-746, Republic of Korea
In metallic magnets, magnetic quantum fluctuation often leaves ubiquitous fingerprints in the
transport properties by showing ’strange-metallic’ behavior or exhibiting anomalies related to
the formation of an exotic order. Insulating magnets can in principle display such signatures in
the dielectric properties; however, their inherently weak spin-lattice coupling has made the
experimental observations challenging. Here, we present experimental and theoretical
evidences for antiferromagnetic quantum fluctuations that manifest in the dielectric properties
of the multiferroic Ba2CoGe2O7, wherein antiferromagnetism and ferroelectricity are strongly
coupled. Upon application of a magnetic field (H) along the c-axis, the dielectric constant shows
a characteristic power-law dependence near absolute zero temperature (T) at the critical field
Hc = 37.1 T due to enhanced antiferromagnetic quantum fluctuations. When H is further
increased beyond Hc, the T-dependence of the dielectric constant shows clear anomalies that
are coupled to a crossover from a field induced polarized state to a gapped quantum paramagnet.
We uncover theoretically that a linear relation between antiferromagnetic susceptibility and
dielectric constant stems from the generic magnetoelectric coupling and directly explains the
experimental findings, opening a new pathway for studying quantum critical phenomena in
condensed matter.
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[O19] High mobility, stability, and bipolar dopability of transparent
perovskite semiconductor BaSnO3
Kookrin Char
Center for Stronlgy Correlated Materials Research
Dept. of Physics and Astronomy
Seoul National University
We have recently discovered that a perovskite BaSnO3 exhibits high mobility at room
temperature when doped with La in the Ba sites. We will go over the mechanism for the high
mobility, especially when compared with Sb doping in the Sn sites. We will discuss the large
effect of threading dislocations on the mobility of epitaxial thin films on SrTiO3 substrates. In
addition, a very stable oxygen stoichiometry in BaSnO3 system has been measured.
Such high chemical stability promises a large potential for well-defined interface in
heterostructures based on them. To demonstrate in this direction, we will present our current
research efforts in pn-junctions and FETs based on the BaSnO3 system. Furthermore, 2DEG
based on the BaSnO3 system can shed light on the exact mechanism of 2DEGs found at the
interfaces of polar perovskites. We will report on our recent findings in this area as well. To
further evaluate its potential for perovskite science, strongly correlated effects of 4d or 5d
doping in the Sn sites are investigated.
Due to high-mobility, chemical stability, and bipolar dopability, the BaSnO3 system promises
a large potential to combine semiconductor and perovskite science and technology.
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[O20] Photoinduced dynamics of spinel MnV2O4 as a spin-orbital coupled
system
Takuro Katsufuji
Department of Physics, Waseda University, Tokyo 169-8555, Japan
Spinel MnV2O4 is a d2 Mott insulator and exhibits a simultaneous magnetic and orbital ordering
accompanied by a structural phase transition at 57 K. It is known that Al doping into the V site
suppresses the orbital ordering and the structural phase transition but keeps the magnetic
ordering almost unchanged. We studied the photoinduced dynamics of MnV2O4 and
MnV1.8Al0.2O4 by pump-probe optical reflectivity measurements [1-3]. We found that the
photoinduced dynamics of these compounds can be separated into three components, (1) the
immediate (<1 ps) suppression of the Mott-excitation peak, (2) the melting of the orbital
ordering, which results in the anisotropic change of the spectra, and (3) the melting of the
magnetic ordering, which occurs several picoseconds after the photoirradiation. Such a
relatively slow dynamics in the melting of the magnetic ordering is caused by the lower energy
scale in magnetism compared with the transfer energy of the electrons dominating the
suppression of the Mott excitation.
Reference:
[1] T Katsufuji et al., Phys. Rev. B 87, 054424 (2013).
[2] A. Furuhashi et al., Phys. Rev. B 88, 060410(R) (2013).
[3] K. Takubo et al., Phys. Rev. B, in press.
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[O21] Exotic electronic phases derived from semi-metals+
Hide Takagi
Department of Physics, University of Tokyo, Hongo, Tokyo113-0022, Japan
Max Planck Institute for Solid State Research, Stuttgart 70569, Germany
Exotic electronic phases sometimes emerge in low carrier density semimetals, due to interplay
of electrons and holes with Coulomb interaction and spin-orbit coupling. I will be talking
about recent progress of our materials exploration, with emphasis on such exotic phases derived
from semi-metals. The topics will include 1. excitonic transition in Ta2NiSe5, 2. a spin-orbital
semimetal to a magnetic insulator transition in SrIrO3/SrTiO3 super-lattice and, if time allows,
3. three-dimensional Dirac electrons in anti-perovskites.
+Work done in collaboration with A. Rost, T. Takayama, J.Matsuno, Y.Lu and D.Hirai
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[O22] Geometric Hall Effect in a Spinor Bose-Einstein Condensate with a
Skyrmion Spin Texture
Yong-il Shin
Department of Physics and Astronomy, Seoul National University, Seoul, Korea
When a spin-carrying particle slowly moves in a spatially varying magnetic field, it acquires
the Berry phase which orginates from the geometric structure of the magnetic field. From this
geometric phase, effective magnetic and electric forces can arise for the particle, even when it
is electrically neutral. Recently, fictitious electromagnetism due to non-trivial spin textures has
been studied in many areas of physics, e.g. to understand the anomalous Hall effect in magnetic
materials and for spintronics applications. In this talk, I will introduce spinor Bose-Einstein
condensates of neutral atoms with skrymion spin textures [1,2] and present our experimental
observation of a geometric Hall effect in the spinor superfluid system [3]. When the condensate
was driven in one direction to oscillate with respect to the spin texture, we observed the
development of its transverse motion perpendicular to the driving direction and the effective
field direction, demonstrating the existence of an effective Lorentz force in the system. Under
a resonant drive, the center of mass of the condensate showed a circular motion around the
center of the skyrmion spin texture and in particular, quantized vortices were nucleated in the
circulating condensate. We observed that the growth rate of the vortex number increases with
the effective field strength, i.e. the Berry curvature of the skyrmion spin texture.
Reference:
[1] J. Choi, W. J. Kwon, and Y. Shin, Phys. Rev. Lett. 108, 035301 (2012).
[2] J. Choi et al., New J. Phys. 14, 053013 (2012).
[3] J. Choi, S. Kang, S. W. Seo, W. J. Kwon, and Y. Shin, Phys. Rev. Lett. (to be published).
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[O23] Strong increase of Tc of Sr2RuO4 under both tensile and compressive
strain
Clifford W. Hicks1,2, Daniel O. Brodsky2, Edward A. Yelland2,3, Alexandra S. Gibbs, Jan A.
N. Bruin, Keigo Nishimura4, Shingo Yonezawa4, Yoshiteru Maeno4, Andrew P. Mackenzie1,2
1
Max Planck Institute for Chemical Physics of Solids, Nothnitzer Strabe 40, Dresden 01187,
Germany
2
Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University
of St. Andrews, St. Andrews KY16 9SS, United Kingdom
3
SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions,
University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom
4
Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502,
Japan
The superconductor Sr2RuO4 has been thought for nearly twenty years to have a px+ipy order
parameter, which would make Sr2RuO4 a two-dimensional electronic analogue of superfluid
3He, and would be a unique order parameter among known superconductors. But definitive
demonstration has proved difficult. The crystal symmetry of Sr2RuO4 is tetragonal, and lifting
the tetragonal symmetry by straining the crystal should lift the degeneracy between the px and
py components. There should be a characteristic response at zero strain, where the order
parameter switches between px and py. To test this hypothesis, we built apparatus capable of
applying up to 0.25% compressive and tensile strain. Tc of Sr2RuO4 was found to increase
strongly under both tensile and compressive strains along the crystallographic <100> directions,
but is only weakly affected by <110> strains. As well as advancing our understanding of
Sr2RuO4, this technique has potential applicability to a wide range of problems in sold-state
physics.
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[O24] Skyrmionics
Maxim Mostovoy
Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4,
9747 AG, Groningen, The Netherlands
Skyrmions are non-coplanar topological defects in ordered states with vector order parameters.
Their non-trivial topology is a source of interesting physics. First introduced by T. H. R. Skyrme
in his unified theory of baryons and mesons, they have been recently discussed as excitations
in Quantum Hall ferromagnets and building blocks of crystal-like spin superlattices in complex
magnets. Skyrmions have been observed in magnetic materials with a non-centrosymmetric
crystal lattice, such as ferromagnetic metallic MnSi and ferromagnetic insulator Cu2OSeO3,
using small-angle neutron scattering and Lorentz microscopy. I will discuss mechanisms for
stability of skyrmions and new classes of magnetic materials in which these fascinating
topological defects can be found.
The Berry phase acquired by the wave function of the electron propagating through the noncoplanar spin configuration of skyrmion makes possible to identify skyrmion with a quantized
flux of an effective magnetic field. This field gives rise to skew scattering of electrons off
skyrmions and the resulting reaction force moves skyrmions along the direction of electrical
current. Moving skyrmions induce effective electric fields which accelerate electrons. These
effects give rise to complex coupled dynamics of electrons and skyrmions mediated by effective
electromagnetic fields. It was recently shown that, like electrons, magnons also “feel” the
effective magnetic field of skyrmions and that thermally-induced magnon currents induce spin
torques that can set skyrmions into motion. This opens possibility to build all-spin analogues
of electronic devices, in which skyrmions are controlled with magnon currents. I will discuss
thermoelectric effects resulting from the coupled dynamics of electrons, magnons and
skyrmions.
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[O25] Dirac vs. Weyl in topological insulators: Adler-Bell-Jackiw anomaly
in transport phenomena
Ki-Seok Kim
Department of Physics, POSTECH, Pohang 790-784, Korea
Dirac metals (gapless semi-conductors) are believed to turn into Weyl metals when
perturbations, which break either time reversal symmetry or inversion symmetry, are employed.
However, no experimental evidence has been reported for the existence of Weyl fermions in
three dimensions. Applying magnetic fields near the topological phase transition from a
topological insulator to a band insulator in Bi1-xSbx, we observe not only the weak antilocalization phenomenon in magnetoconductivity near zero magnetic fields (B < 0.4 T) but also
its upturn above 0.4 T only for E // B. This “incompatible” coexistence between weak antilocalization and “negative” magnetoresistivity is attributed to the Adler-Bell-Jackiw anomaly
(“topological” theta-term) in the presence of weak anti-localization corrections.
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[O26] Quantum anomalous Hall effect in magnetically doped topological
insulator
Ke He
State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics,
Tsinghua University, Beijing 100084, China
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, The Chinese
Academy of Sciences, Beijing 100190, China
Keywords: quantum anomalous Hall effect, topological insulator, magnetic doping
Quantum Hall effect (QHE), one of the most important quantum phenomena in modern
condensed matter physics, results from Landau quantization of a two-dimensional electronic
system under strong magnetic field [1]. It has long been expected that QHE may occur without
Landau levels so that neither external magnetic field nor high sample mobility is required for
its studies and applications [2,3]. The QHE free of Landau levels can be realized in topological
insulators (TIs) [3-7] with ferromagnetism as the quantized version of the anomalous Hall effect
[3], i.e., the quantum anomalous Hall effect (QAHE). With molecular beam epitaxy [8], we
have prepared thin films of Cr-doped (Bi,Sb)2Te3 TIs with well-controlled composition,
thickness [8] and chemical potential [9], which exhibit long range ferromagnetism even in
insulating phase [10]. In such thin films, we eventually observed the quantization of the Hall
resistance at h/e2 at zero field, accompanied by a considerable drop in the longitudinal resistance,
which can completely vanish under a strong magnetic field. These observations unambiguously
demonstrate the realization of the QAHE [11]. The observation of the QAHE not only
concludes the decades-long search for zero field quantum Hall effect but represents a start point
for exploration and applications of various topological quantum phenomena in the future.
Reference:
[1] S. M. Girvin, The Quantum Hall effect. Springer-Verlag, New York (1990).
[2] F. D. M. Haldane, Phys Rev Lett 61 (1988) 2015.
[3] N. Nagaosa, J. Sinova, S. Onoda, A. H. MacDonald, and N. P. Ong, Rev Mod Phys 82 (2010) 1539.
[4] M. Z. Hasan and C. L. Kane, Rev Mod Phys 82 (2010) 2045.
[5] X. -L. Qi and S. -C Zhang, Rev Mod Phys 83 (2011) 1057.
[6] R. Yu, W. Zhang, H. Zhang, S. -C. Zhang, X. Dai, and Z. Fang, Science 329 (2010) 61.
[7] K. Nomura and N. Nagaosa, Phys Rev Lett 106 (2011) 166802.
[8] X. Chen, X. -C. Ma, K. He, J. -F. Jia, and Q. -K. Xue, Adv. Mater. 23 (2010) 1162.
[9] J. Zhang, C. -Z. Chang, Z. Zhang et al., Nature Commun. 2 (2011) 574.
[10] C. -Z. Chang, J. Zhang, M. Liu et al., Adv. Mater. 25 (2013) 1065.
[11] C. -Z. Chang, J. Zhang, X. Feng, J. Shen et al., Science 340 (2013) 167.
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[O27] Odd interactions in quantum magnets and liquids
Sasha Chernyshev
UC Irvine
I will discuss several scenarios in which interactions of excitations in quantum magnets and
liquids give rise to unusual phenomena. Two of the principal cases concern the role of threeparticle interactions in the spectra of the non-collinear frustrated antiferromagnets and quantum
liquids such as 4He. The other case study shows that the effect of random disorder may dwarf
the conventional magnon-magnon scattering in a different class of antiferromagnets with XY
anisotropy. Our results have strong support from the high-resolution neutron resonance spinecho experiments. Implications for the other systems are offered.
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[O28] Observation of magnon decay and non-linear spin waves in LuMnO3
M. D. Le1,2
1
Center for Correlated Electron Systems, Institute for Basic Science, Seoul, Korea
Department of Physics and Astronomy, Seoul National University, Seoul, Korea
2
We report the observation of magnon decay in a non-collinear antiferromagnet, LuMnO3, in
line with recent theoretical work. This member of the rare earth hexagonal manganites
possesses a triangular lattice of Mn3+ ions with spin S=2, which adopts the non-collinear 120
degrees order below TN=90K. At certain points in the Brillouin zone, the highest energy spin
wave mode becomes exceptionally broad, indicative of its decay into two magnons. Additional
features of the spin wave dispersion also point to a departure from linear spin wave
theory. The system is further complicated by a trimerisation of the spins due to a giant offcentering of the Mn ions in the triangular plane, which allows short ranged correlations to
persist well above TN. These features have, as yet, no complete theoretical treatment, but we
will present new polarised inelastic scattering data which may shed light on the problem.
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[O29] Defects in spin ice
J. Goff
RHL, London
The idea of magnetic monopoles in spin ice has enjoyed much success at intermediate
temperatures, but at low temperatures a description in terms of monopole dynamics alone is
insufficient. Recently, numerical simulations were used to argue that magnetic impurities
account for this discrepancy by introducing a magnetic equivalent of residual resistance in the
system. Here we propose that oxygen deficiency is the leading cause of magnetic impurities in
as-grown samples, and we determine the defect structure and magnetism using diffuse neutron
scattering and magnetization measurements. From crystal field calculations we find that oxygen
vacancies in spin ice cause the rare-earth anisotropy to change to easy plane. We further argue
that these magnetic defects may be capable of trapping monopoles at sub-Kelvin temperatures.
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[O30] Many Body Physics in Graphene with ARPES
A. Bostwick
Advanced Light Source, Lawrence Berkeley National Laboratory, USA
Graphene is a remarkable new electronic material with many unique properties. To realise its
promise, it is essential to understand its the electronic structure. By measuring the spectral
function of charge carriers using angle resolved photoemission from various type of graphene
grown on SiC, we show that it is possible to develop a broad understanding of the electronic
structure and many body interactions in graphene. We also show that the structure of the
graphene and substrate on which it is placed play a key role in determining both the basic band
structure and the strength and type of many body interactions.
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[O31] Spin-orbital entangled jeff states in 4d and 5d transition metal systems
Hosub Jin1,2
1
Center for Correlated Electron Systems, Institute for Basic Science, Seoul , Korea
Department of Physics and Astronomy, Seoul National University, Seoul, Korea
2
The discovery of the so-called jeff =1/2 state in the layered 5d transition metal oxide Sr2IrO4 has
provided a new viewpoint in understanding the electronic and magnetic properties of the system
containing large spin-orbit coupling [1]. The spin-orbital entangled nature of the jeff state can
host various exotic phases with the help of electron correlations [2]. In this talk, we suggest that
a series of 4d and 5d transition metal compounds, AM4X8, host the molecular form of the jeff
state in their low energy electronic structures. Wide range of electron correlations are accessible
by means of tuning the bandwidth under the external and/or chemical pressure, enabling us to
investigate the interesting cooperation between SOC and electron correlations. On the way to
search the possibility of the various emergent phases with respect to the competing electron
correlation strength, we briefly elucidate the topological insulating phase and the complicated
spin model in the weak and strong coupling limit, respectively.
Reference:
[1] B. J. Kim et al., Phys. Rev. Lett. 101, 076402 (2008).
[2] For a review, see W. Witczak-Krempa, G. Chen, Y. B. Kim, and L. Balents, rXiv:1305.2193
(2013).
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[O33] Neutron scattering studies of the kagomé lattice: quantum spin
liquids and topological magnon bands
Young Lee
Department of Physics, Massachusetts Institute of Technology,
Cambridge, MA 02139, USA
I will describe experimental studies of new states of magnetism on the S=1/2 kagomé lattice,
focusing on two materials: one with antiferromagnetic exchange and one with ferromagnetic
exchange. Quantum spin liquids are new states of matter that are characterized by long-range
entanglement and support exotic excitations. After 40 years since the original proposal for such
a state by Anderson, these systems have only recently been realized in experiments.
Herbertsmithite is a leading candidate for having a quantum spin liquid (QSL) ground state. A
recent breakthrough in crystal growth has allowed us to uncover a hallmark signature of the
QSL state. Inelastic neutron scattering measurements reveal that the spin excitations are
fractionalized, a remarkable first. Additional measurements, made possible by the crystals,
further corroborate the identification of a QSL. In contrast to the antiferromagnetic case,
ferromagnetic moments on the kagomé lattice are not highly frustrated. Our neutron scattering
measurements on Cu(1,3-bdc) confirm that the spins order at low temperatures. However,
inelastic scattering reveals an interesting flat band in the magnon dispersion relations. Moreover,
each band is separated by a gap from the other bands. I will discuss the role of the
Dzyaloshinsky-Moriya interaction and the prospects of measuring new physics with
topologically non-trivial magnon bands.
Reference:
1. T.-H. Han, J.S. Helton, S. Chu, D.G. Nocera, J.A. Rodriguez-Rivera, C. Broholm, and Y.S. Lee,
Nature 492, 406 (2012).
2. T.H. Han, S. Chu, and Y.S. Lee, Phys. Rev. Lett. 108, 157202 (2012).
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[O34] Quantum and thermal criticality in magnets
Christian Ruegg
Laboratory for Neutron Scattering, Paul Scherrer Institute, Switzerland Department of
Condensed Matter Physics, University of Geneva, Switzerland
A quantum--‐disordered ground state with a spin gap is separated in three-dimensional dimer
antiferromagnets by a quantum critical point (QCP) from a phase with long-range
antiferromagnetic order and finite ordering temperature [1]. While this QCP has been studied
intensely in theoretical and numerical work by bond-operators and quantum Monte-Carlo, real
materials in which it can be explored experimentally are rare. In the material TlCuCl3 this QCP
was studied in great detail by neutron scattering and other techniques. These experiments
provide unprecedented insights into quantum and thermal criticality and the elementary
excitations near QCPs. A defining phenomenon is the emergence of longitudinal modes near
the QCP [2], which are the Higgs excitations of dimer antiferromagnets [3], and their role in
quantum and classical criticality [4].
Reference:
[1] S. Chakravarty, B.I Halperin, and D.R. Nelson, Phys. Rev. B 39, 2344 (1989).
[2] Ch. Ruegg et al., Phys. Rev. Lett. 100, 205701 (2008).
[3] S. Sachdev and B. Keimer, Physics Today 64, 29 (2011) and arXiv:0901.4103.
[4] P. Merchant et al., submitted.
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[O35] Correlation effects in skew scattering mechanisms of Anomalous and
Spin Hall Effects
Timothy Ziman1, 2
1
2
Institut Laue Langevin, Boîte Postale 156, 38042 Grenoble Cedex 9, France
LPMMC (UMR 5493), CNRS/ Université Joseph Fourier, 38042 Grenoble, France
Skew scattering of electrons in ferromagnetic metals can produce the anomalous and spin Hall
effects. The microscopic mechanism is normally considered to be either the intrinsic effect of
the crystal lattice or scattering from impurities, with the spin-orbit interaction in each case
providing the coupling between the spin and the displacement of the electrons. As this is a
relativistic effect it is weak, and this is one of the obstacles to making and detecting spin currents.
It is interesting to see whether effects of correlations can enhance the skew scattering and I will
discuss this. In a ferromagnetic metal, scattering can also be from collective spin fluctuations,
and we might expect these to be especially significant near the Curie temperature. Recently,
with Bo Gu and S. Maekawa (ASRC, JAEA), we have extended Kondo's theory of the
anomalous Hall effect to include short range spin-spin correlations and to find the spin hall
coefficients. We find a novel relation of the transport coefficients to three- and four-spin
correlations near the Curie temperature Tc the respective anomalous and spin hall coefficients.
Our theory can be compared to recent experimental results by Wei et al [Nature Commun. 3,
1058 (2012)] for the ISHE in ferromagnetic alloys.
Figure 1: Schematic behavior of the anomalous (left) and spin Hall resistances (right) around
Tc. In each case the power-law divergence (dashed lines) of the corresponding non-linear
susceptibility x1 or x2 is cut off by the finite Fermi surface. The different shapes (solid lines) of
the anomalies reflect that the third order correlations vanish about Tc and the fourth order
correlations change sign across Tc.
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2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
[O36] Quasiparticle carrier dynamics in graphene from first principles
Cheol Hwan Park
Department of Physics and Astronomy, Seoul National University, Seoul 151-747, S. Korea
It is usually very important to understand how a charge carrier in real materials interacts with
other charge carriers and lattice vibrations; these two effects, electron-electron and electronphonon interactions, respectively, largely determine the quasiparticle and transport properties
of a material. In this presentation, we will show that some important aspects of quasiparticle
dynamics in graphene can be described by first-principles calculations considering these two
effects together.
40
2014 Quantum Materials Symposium
Muju Deogyusan Resort, Korea
[O37] Recent Thz results on quantum correlated matter
P. Armitage
Johns Hopkins University, USA
The occurrence of novel quantum phenomena emergent on the longest length scales heightens
the need for new experimental tools that probe finite, yet long time scales (compared to typical
electronic ones). This talk will review recent advances in the area of THz spectroscopy and its
application to exotic quantum states of matter. I will give examples on material systems as
diverse as topological insulators, 1D quantum spin systems, and cuprate superconductors. A
desire to characterize materials in a novel fashion and answer specific scientific questions is
driving the technology forward, while new technology is changing the kinds of scientific
questions we dare to ask.
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