discussion_week3_FeSe - Magnetism, Bad Metals and
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Review of results on FeSe P Hirschfeld, 9/19 (Data only up to 6/2014) Thanks to: Taka Shibauchi Tetsuo Hanaguri Frederic Hardy (+Anna Boehmer, Christoph Meingast) • Basic properties N and S states • New physics from new crystals Relatively correlated material Z. P. Yin, K. Haule, & G. Kotliar, Nat. Mat. 10, 932–935 (2011) LDA+DMFT exercise: Fix interactions U,J, vary material FeSe: nonmagnetic 8K superconductor, but: ARPES gap Wang et al. Chin. Phys. Lett. 2012 Medvedev et al 2010: Tc37K under pressure 1 layer Tc35K under tensile strain Burrard‐Lucas et al 2012 Tc43K molecular intercalation S. He et al aXv::1207.6823 Pressure dependence of bulk FeSe Margadona et al 2010 Bendele et al 2012: magnetic state at low pressure Medvedev et al 2010 Pressure enhances spin fluctuations Imai, Cava PRL 2009 But note difference from other systems FeSe Spin fluctuations seem to wait until orthorhombic transition happens Are the chalcogenides generally more correlated? “Bad metals”? Fang et al 2009 Morosan et al (Rice group) 2013 Mizuguchi et al 2011 A tale of two Fe-chalcogenides Mizuguchi et al 2011 Kasahara et al, unpublished (2014) crystals from A. Böhmer et al., PRB 87, 180505(R) (2013) r(Tc)~0.1Wcm Bad metal physics not evident in FeSe High-quality stoichiometric FeSe single crystal grown @KIT A. Böhmer et al., PRB 87, 180505(R) (2013). S. Kasahara et al., unpublished? • Tc ~ 10 K (cf. ~8 K for typical samples) • Large RRR and MR indicate that samples are very clean. How good are new KIT crystals really? F.-C. Hsu et al., PNAS 105, 14262 (2008). r0= 250 mWcm at 8K RRR~6.5 S. Kasahara et al., unpublished? r0= 10 mWcm at 10K RRR~40 Consistent with (r(T0) =0) Electronic specific heat old new JY Lin et al, PRB 84, 220507(R) (2011) Hardy et al, unpublished Old and new very similar – small influence of disorder on SC SdH (Terashima arXiv:1405.7749) SdH Large orbital ordering in ARPES Nakayama et al. arXiv:1404..0857 Signatures of electronic nematicity in FeSC generally ARPES: orbital ordering (0,p) (p,0) Yi et al PNAS 2011 (0,p) (p,0) Signatures of electronic nematicity in FeSC STM in SC state FeSe: CL Song et al, Science 2011, PRL 2012 topography spectrum defect vortex a and b are only ~0.1% different! But strong C4 symmetry breaking in SC state. Tunneling spectra High energy spectrum (±95 mV) Low energy spectrum (±6 mV) Multigap SC Unidirectional quasi-particle interference Hanaguri group using KIT crystals FT-dI/dV/(I/V) T ~ 1.5 K Topograph dI/dV/(I/V) Bragg alias bqFe b aqFe a Small orthorhombicity bFe yet large anisotropy in the band aFe structure! 45 nm×45 nm, +50 mV/100 pA Unidirectional dispersing features in qa and qb directions. cf. NaFeAs: E. P. Rosenthal et al., Nat. Phys. 10, 225 (2014). QPI Bandstructure (note: over small 1-domain window!) along qa B = 12 T B = 12 T imp. +D -D along qb FT-dI/dV/(I/V) EF Electron-like EF imp. +D -D Hole-like • Orthogonal electron- and hole-like dispersions • Extremely small EF ~ D BCS-BEC crossover regime? Possible intra-orbital scattering • Orbital character changes when we go around the FS pockets. • If only intra-orbital scatterings are allowed, QPI patterns may be unidirectional. • Why one of the orbitals is active? Orbital order? S. Graser et al., New J. Phys. 11, 025016 (2009). Can we reproduce orthogonal electron and hole dispersions using the orbital-order model? Lifting the orbital degeneracy Orbital character Band calc. (by Dr. H. Ikeda) xz Orthorhombic distortion only = 0.05 eV Eyz-Exz = 0.1 eV xy More detailed calculations are indispensable… xz Eyz-Exz yz yz Orthorhombic distortion alone cannot explain the unidrectional dispersions. xy Orthorhomicity is yz xz xy not a player but a spectator. Orbital order? Penetration depth and thermal conductivity results Introduction: FeSex Superconducting gap symmetry ---- A key for the mechanism Thermal Conductivity MBE-STM J.K. Dong, et al., PRB (2009). Specific heat The simplest structure Strong correlation F.C. Hsu, et al., PNAS (2008). J.-Y.Lin, et al., PRB (2011). Can-Li Song, et al., Science 332. 1410 (2010). Single crystals (off-stoichiometry) Defect-free stoichiometric films Nodeless multiple gaps Nodal superconductivity Magnetic field penetration depth Large temperature dependence Quasi T-linear at T/Tc < 0.2 Dl ~T1.4 No Curie term (No excess irons) Finite qusiparticle excitation at low temperatures Presence of line nodes Thermal conductivity in a stoichiometric FeSe single crystal Increase of the quasiparticle life time below Tc Large residual value k0/T~ 0.4 (W/K2m) kn/T Wiedemann-Franz law kn/T=L0/r0 ~ 1.43 (W/K2m) L0: Lorentz number Tc r0 ~ 1.70 mWcm ~ 30-40% of the normal state value Strong evidence for the line nodes Discussion: Origin of the different behavior D Present study (Clean single crystals) Quasi T-linear l(T) Finite residual k0/T f 0 Nodal Superconductivity Accidental nodes Earlier study (Dirty crystals) Negligibly small k0/T at 0 T Gap anisotropy is smeared by strong scattering G D 0 f J.K. Dong, et al., PRB (2009). Nodeless (Anisotropic s-wave) Nodes can be removed Nodal s-wave state in FeSe Discussion: Origin of the different behavior Magnitude of the residual term D Present results 0 x: coherence length ~ 5 nm ~ 0.3-0.4 l: mean free path ~ 200 nm 1/m ~ 6 - 8 node Inconsistent with d-wave Slope parameter of gap at nodes Nodes are nearly vanishing G D f Accidental nodes Gap anisotropy is smeared by strong scattering 0 D f 0 f 2-band model V. Mishra et al., PRB, 80, 224525 (2009). Nodes can be removed Nodal s-wave state in FeSe Anomalous field dependence of thermal conductivity Strong reduction of k/T at low fields FeSe Plateau at high fields kel/T ~ N(EF)vFl Different from ordinal behaviors Doppler shift N(E)~ H1/2 m0 Anomalous field dependence of thermal conductivity Strong reduction of k/T at low fields FeSe Plateau at high fields kel/T ~ N(EF)vFl ① Vortex scattering due to long mean free path CeCoIn5 Y. Kasahara et al., PRB, 72, 214515 (2005 Doppler shift N(E)~ H1/2 m0 Long m.f.p. l ~ H-1/2 & vortex scattering(av ~ H-1/2) Cancelation Plateau Anomalous field dependence of thermal conductivity Strong reduction of k/T at low fields FeSe Plateau at high fields kel/T ~ N(EF)vFl ① Vortex scattering due to long mean free path FeSe Magnetoresistance Dr/r0 ~ (wct )2 l =vFt ~ 0.2 mm Long mean free path m0 Hard to explain a sharp kink at low fields and a plateau in a nearly whole vortex state Anomalous field dependence of thermal conductivity Strong reduction of k/T at low fields FeSe Plateau at high fields ② Possible phase transition in the SC state BSCCO Field induced change of gap symmetry dx2-y2 dx2-y2 + idxy or dx2-y2 + is K. Krishana, et al., Science (1997). m0 FeSe s s + id (???) Anomalous field dependence of thermal conductivity Strong reduction of k/T at low fields FeSe Plateau at high fields ③ Lifting nodes under magnetic field m0 V. Mishra et al., Phys. Rev. B, 80, 224525 (2009) Plateau with finite k/T Small SC gap already suppressed at low fields High-field anomaly in thermal conductivity H* 1.0 0.70 0.9 1.5 K k/T (W/K m) 0.8 2 1.12 K 2 k/T (W/K m) 0.65 0.7 0.76 K 0.6 0.76 K 0.60 0.58 K 0.55 0.58 K 0.50 0.39 K 0.45 0.39 K 0.5 0.4 0 4 8 m0H (T) 12 16 0 4 8 m0H (T) 12 16 Proposed new high-fied phase Summary • FeSe Tc very sensitive to pressure • Apparent strong orbital ordering in ARPES, STM, no magnetism strong nematic ordering (resistivity anisotropy???) Big challenge to electronic structure theory! • SC state consistent with weak nodes (easily removed by perturbation)
