Quasiparticle Excitations in the Superconducting State of FeSe Probed by Thermal Hall Conductivity in the Vicinity of the BCS-BEC Crossover

Abstract

There is growing evidence that the superconducting semimetal FeSe ($T_c\sim 8$ K) is in the crossover regime between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits. We report on longitudinal and transverse thermal conductivities, ${\kappa }_{xx}$ and ${\kappa }_{xy}$, respectively, in magnetic fields up to 20 T. The field dependences of ${\kappa }_{xx}$ and ${\kappa }_{xy}$ imply that a highly anisotropic small superconducting gap forms at the electron Fermi-surface pocket whereas a more isotropic and larger gap forms at the hole pocket. Below $\sim 1.0$ K, both ${\kappa }_{xx}$ and ${\kappa }_{xy}$ exhibit distinct anomalies (kinks) at the upper critical field $H_{c2}$ and at a field $H^{\ast }$ slightly below $H_{c2}$. The analysis of the thermal Hall angle (${\kappa }_{xy}/{\kappa }_{xx}$) indicates a change of the quasiparticle scattering rate at $H^{\ast }$. These results provide strong support to the previous suggestion that above $H^{\ast }$ a distinct field-induced superconducting phase emerges with an unprecedented large spin imbalance.

7 pages, 3 figures, to be published in JPSJ

References in corpus (18)

• Theory of ultracold Fermi gases
• Superconductivity at 36 K in beta-Fe1.01Se with the compression of the interlayer separation under pressure
• The Structural Phase Transition in FeSe (Fe1+dSe)
• Fulde-Ferrell-Larkin-Ovchinnikov State in Heavy Fermion Superconductors
• Why Does Undoped FeSe Become A High Tc Superconductor Under Pressure?
• Orbital-driven nematicity in FeSe
• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• Emergence of the nematic electronic state in FeSe
• Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor
• Calorimetric Evidence for a Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in the Layered Organic Superconductor κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$
• Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study
• Ultra-cold Polarized Fermi Gases
• Exotic Superconducting Properties in the Electron-Hole Compensated Heavy Fermion `Semimetal' URu2Si2
• Anomalous Fermi surface in FeSe seen by Shubnikov-de Haas oscillation measurements
• Nodal Structure of Unconventional Superconductors Probed by the Angle Resolved Thermal Transport Measurements
• Giant superconducting fluctuations in the compensated semimetal FeSe at the BCS-BEC crossover
• Larkin-Ovchinnikov state in resonant Fermi gas
• Flux Line Lattice Melting and the Formation of a Coherent Quasiparticle Bloch State in the Ultraclean URu${}_2$Si${}_2$ Superconductor

Cited by in corpus (13)

• Nematicity, magnetism and superconductivity in FeSe
• The key ingredients of the electronic structure of FeSe
• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Exotic Superconducting States in FeSe-based Materials
• Evidence for an FFLO state with segmented vortices in the BCS-BEC-crossover superconductor FeSe
• Hydrostatic and uniaxial pressure tuning of iron-based superconductors: Insights into superconductivity, magnetism, nematicity and collapsed tetragonal transitions
• Pseudogap Behavior of the Nuclear Spin-lattice Relaxation Rate in FeSe Probed by ${}^{77}$Se-NMR
• Microscopic mechanism for fluctuating pair density wave
• Quasiparticle Nodal Plane in the Fulde-Ferrell-Larkin-Ovchinnikov State of FeSe
• Vortex-lattice melting and paramagnetic depairing in the nematic superconductor FeSe
• Multi-band description of the upper critical field of bulk FeSe
• Superconductivity of highly spin-polarized electrons in FeSe probed by ${}^{77}$Se NMR
• Intrinsic pinning of FeSe${}_1$${}_{-}$${}_x$S${}_x$ single crystals probed by torque magnetometry