8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Serguei L. Molodtsov, European XFEL & Freiberg University of Technology
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Cooperators
Studies were performed by:
Dresden University :
ESRF (ID16):
Spring-8 (BL25SU):
MPI CPfS Dresden:
K. Kummer (ESRF) , D. Vyalikh,
Yu. Kucherenko, S. Danzenbächer,
M. Holder, C. Laubschat
S. Huotari and L. Simonelli
T. Muro, Y. Kato and T. Kinoshita
C. Krellner and C. Geibel
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Correlated f-materials
Periodic table n m 2
[Xe] 4f 5d 6s
Atomic potential
3
Lanthanoide
:
S.L. Molodtsov, European XFEL & TU Freiberg f - electrons
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Correlated f-materials: YbRh
2
Si
2
4
Correlated f-Materials
Periodic table of the elements
Lanthanoide
:
S.L. Molodtsov, European XFEL & TU Freiberg f - electrons
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Correlated f-materials: Mixed-valent Ce and Yb systems
E
DOS f d e
E
F f
1 f d
DOS
E e f
0
E
F f electron promotion energy U fd may be compensated by increase of the system cohesive energy
D
U
C
5
U fd
U fd
>>
D
U
C
– stable configuration f n [f 1 for Ce; f 14 (h 0 ) for Yb]
<<
D
U
C
– stable configuration f n-1 [f 0 for Ce, f 13 (h 1 ) for Yb]
U fd
~ D
U
C
– mixed-valent system f v , (n-1) < v < n
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
From mixed-valent to Kondo behavior (Ce)
E
6
Why exact knowledge of intermediate valency is important ?
e f
2 f states
U ff
Mixed valence: e f
1 and e f
0 are almost equally possible short lifetime efficient hopping broad E
F peak
Kondo e f
0
E
F e f
1
U fd
Kondo: starting from e f
1 , probability to have e f
0 is very low hopping is rear long lifetime sharp Kondo resonance
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermediete valency from photoemission
SIAM calculations
Ce:
ε f
= -1.5 eV
Δ = 1.0 eV
Yb:
ε f
= -0.05 eV
Δ = 0.3 eV
U ff
= 7 eV
J.-M. Imer & E. Wuilloud,
Z. Phys. B 66 , 153 (1987).
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GSP breaks down, since it underestimates experimental intensity at E
F
. Final-state hybridization should be included in consideration!
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Final-state hybridization is included!
SIAM calculations
Ce:
ε f
= -1.5 eV
Δ = 1.0 eV
Yb:
ε f
= -0.05 eV
Δ = 0.3 eV
U ff
= 7 eV
O. Gunnarsson &
K. Schönhammer,
PRB 31 , 4815 (1985)
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In case final state hybridization and finite valence-band width are considered better agreement between theory and experiments can be achieved
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermediete valency of YbRh
2
Si
2 from photoemission
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Divalent (2 + ) contribution into the ground state is considerably overestimated in photoemission experiments
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
RIXS at L
3 edge
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2 p 5 4 f 14 configuration energetically preferred due to its better core-hole screening. Because of possible d
→ f electron hopping, the 2 + line thus might enter overemphasized into the spectra
Constant emission energy (CEE) and constant excited energy (CXE) spectra can be calculated
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermediarte valency from RIXS
CXE at excitation energy of 2 + resonance is preferable for analysis of almost 3 + system
11 with ζ = 1 for CEE scan and ζ < 1 for CXE scan
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermetallic rare-earth materials: YbRh
2
Si
2 12
Typical single-crystalline samples
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermetallic rare-earth materials: YbRh
2
Si
2
Yb
Rh
Si
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Quasi-layered structure, cleave between Yb (blue) and Si (green) layers
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Characterization of cleaved samples: YbRh
2
Si
2
Yb
Rh
Si
14
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Characterization of cleaved samples: YbRh
2
Si
2
15
Yb
Rh
Si
Bulk
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Evaluation of photoemission spectra
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Best fit for Δ = 0.26 eV
S.L. Molodtsov, European XFEL & TU Freiberg
Intermediate valency 2.93 for bulk is observed
(2.88 in GSP)
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Evaluation of RIXS spectra
Intensity map of the Yb Lα
1 fluorescence yield for YbRh
2
Si
2
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CEE and CXE cuts through the 2 + resonance are indicated by white and red circles, respectively
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
CEE cut through the intensity map
XAS measured in total fluorescence yield (TFY) mode and RIXS spectra in
CEE mode of YbRh
2
Si
2
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Spectral broadening is no longer defined by the lifetime of the deep 2p core hole
(TFY-XAS), but by the much shallower 3d core hole (CEE)
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
CXE cut through the intensity map
Emission intensity curve along the CXE cut (excitation into 2 + resonance) indicated by red circles in fig. below
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Originally small 2 + intensity is now comparable to that of the
3 + resonance, despite the only small 2 + divalent admixture in the ground state.
But, further normalization is required!
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Absolute intensity normalization
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ζ = 0 .
13
Information on the absolute intensity ratio between the 2 + and 3 + peaks in their respective resonance maxima can be obtained comparing CEE and CXE cuts crossing maximum of the 2 + signal in the intensity map
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Evaluation of RIXS spectra
Δ = 0.26 eV from photoemission
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Intermediate valency: 2.93 from CEE scan and 2.92 from CEE scan
(2.89 and 2.88 in GSP)
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Summary
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Valency 2.95 is inferred from low-excitation measurements of the
Kondo temperature (20 K)
Both RIXS and photoemission approaches to determine valency fail if only initial-state properties are accounted for
(2 + contribution is overestimated)
Consideration of final-state hybridization is necessary to obtain correct valency
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
European XFEL (XFEL.EU)
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Superconducting LINAC technology provides 27.000 light pulses/s with duration down to a few fs each. It makes XFEL.EU attractive for photonhungry and time-resolved experiments.
S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Heisenberg RIXS (hRIXS) @ XFEL.EU
: Alexander Föhlisch, Helmholtz-
Zentrum-Berlin, Potsdam University, Germany
: Cooperation of representatives of 20 distinguished research institutions from
7 European countries:
Germany, Italy, Switzerland,
Sweden, the Netherlands,
Finland and France
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Experimental hall
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Soft X-ray hall (SASE3): Floor plan
42.5 m
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Completion of underground construction (06.06.13)
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Tunnels: Infrastructure installation
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
European XFEL: Campus
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Main building: Architect ’s view
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S.L. Molodtsov, European XFEL & TU Freiberg
8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Main building: Architect ’s view
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8 th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
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S.L. Molodtsov, European XFEL & TU Freiberg