Superconductivity of highly spin-polarized electrons in FeSe probed by ${}^{77}$Se NMR

Abstract

A number of recent experiments indicate that the iron-chalcogenide FeSe provides the long-sought possibility to study bulk superconductivity in the cross-over regime between the weakly coupled Bardeen--Cooper--Schrieffer (BCS) pairing and the strongly coupled Bose--Einstein condensation (BEC). We report on ${}^{77}$Se nuclear magnetic resonance experiments of FeSe, focused on the superconducting phase for strong magnetic fields applied along the $c$ axis, where a distinct state with large spin polarization was reported. We determine this high-field state as bulk superconducting with high spatial homogeneity of the low-energy spin fluctuations. Further, we find that the static spin susceptibility becomes unusually small at temperatures approaching the superconducting state, despite the presence of pronounced spin fluctuations. Taken together, our results clearly indicate that FeSe indeed features an unusual field-induced superconducting state of a highly spin-polarized Fermi liquid in the BCS-BEC crossover regime.

6 pages, 4 figures

References in corpus (32)

• The Puzzle of High Temperature Superconductivity in Layered Iron Pnictides and Chalcogenides
• Superconductivity in Iron Compounds
• Superconductivity in single-layer films of FeSe with a transition temperature above 100 K
• Superconductivity at 36 K in beta-Fe1.01Se with the compression of the interlayer separation under pressure
• Phase Diagram and High Temperature Superconductivity at 65 K in Tuning Carrier Concentration of Single-Layer FeSe Films
• Stretched Exponential Relaxation Arising from a Continuous Sum of Exponential Decays
• Orbital-driven nematicity in FeSe
• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• BCS-BEC Crossover and the Unitary Fermi Gas
• Strong Interplay between Stripe Spin Fluctuations, Nematicity and Superconductivity in FeSe
• Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study
• Lack of coupling between superconductivity and orthorhombic distortion in stoichiometric single-crystalline FeSe
• Commensurate Itinerant Antiferromagnetism in BaFe2As2: 75As-NMR Studies on a Self-Flux Grown Single Crystal
• Nematicity and quantum paramagnetism in FeSe
• Anomalous Fermi surface in FeSe seen by Shubnikov-de Haas oscillation measurements
• Fe-based superconductors: seven years later
• Giant superconducting fluctuations in the compensated semimetal FeSe at the BCS-BEC crossover
• Electronic nematic susceptibility of iron-based superconductors
• Evidence for an FFLO state with segmented vortices in the BCS-BEC-crossover superconductor FeSe
• Microscopic study of the Fulde-Ferrell-Larkin-Ovchinnikov state in an all-organic superconductor
• Antiferromagnetism of SrFe2As2 studied by Single-Crystal 75As-NMR
• Thermal Conductivity of the Iron-Based Superconductor FeSe : Nodeless Gap with Strong Two-Band Character
• Nuclear magnetic resonance in the heavy fermion superconductors
• Spin Fluctuations and Unconventional Superconductivity in the Fe-based Oxypnictide Superconductor LaFeAsO_0.7 probed by 57Fe-NMR
• Superfluid density and microwave conductivity of FeSe superconductor: ultra-long-lived quasiparticles and extended s-wave energy gap
• 75As NMR-NQR study in superconducting LiFeAs
• Pseudogap Behavior of the Nuclear Spin-lattice Relaxation Rate in FeSe Probed by ${}^{77}$Se-NMR
• Observation of the in-plane magnetic field-induced phase transitions in FeSe
• Spin-Orbital-Intertwined Nematic State in FeSe
• Close proximity of FeSe to a magnetic quantum critical point as revealed by high-resolution $\mu$SR measurements
• Quasiparticle Excitations in the Superconducting State of FeSe Probed by Thermal Hall Conductivity in the Vicinity of the BCS-BEC Crossover
• Singular magnetic anisotropy in the nematic phase of FeSe

Cited by in corpus (5)

• Non-symmorphic symmetry and field-driven odd-parity pairing in CeRh${}_2$As${}_2$
• Quasiparticle Nodal Plane in the Fulde-Ferrell-Larkin-Ovchinnikov State of FeSe
• Spin fluctuations from Bogoliubov Fermi surfaces in the superconducting state of S-substituted FeSe
• Suppression of nematicity by tensile strain in multilayer FeSe/SrTiO${}_3$ films
• Quasiparticle interaction originating from Bogoliubov Fermi Surfaces under pressure in 18%-S substituted FeSe studied via NMR