Superfluid density and microwave conductivity of FeSe superconductor: ultra-long-lived quasiparticles and extended s-wave energy gap

Abstract

FeSe is an iron-based superconductor of immense current interest due to the large enhancements of Tc that occur when it is pressurized or grown as a single layer on an insulating substrate. Here we report precision measurements of its superconducting electrodynamics, at frequencies of 202 and 658 MHz and at temperatures down to 0.1 K. The quasiparticle conductivity reveals a rapid collapse in scattering on entering the superconducting state that is strongly reminiscent of unconventional superconductors such as cuprates, organics and the heavy fermion material CeCoIn5. At the lowest temperatures the quasiparticle mean free path exceeds 50 micron, a record for a compound superconductor. From the superfluid response we confirm the importance of multiband superconductivity and reveal strong evidence for a finite energy-gap minimum.

7 pages, 3 figures

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• Orbital selective pairing and gap structures of iron-based superconductors
• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Exotic Superconducting States in FeSe-based Materials
• Enhancement of Tc by point-like disorder and anisotropic gap in FeSe
• Superconducting gap structure of FeSe
• Thermal Conductivity of the Iron-Based Superconductor FeSe : Nodeless Gap with Strong Two-Band Character
• Single-gap superconductivity and dome of superfluid density in Nb-doped SrTiO3
• Nodal gaps in the nematic superconductor FeSe from heat capacity
• Highly anisotropic superconducting gaps and possible evidence of antiferromagnetic order in FeSe single crystals
• Superconductivity-enhanced Nematicity and '$s+d$' Gap Symmetry in Fe(Se${}_{1-x}$S${}_x$)
• Itinerant approach to magnetic neutron scattering of FeSe: effect of orbital selectivity
• Evidence of nodal gap structure in the basal plane of the FeSe superconductor
• Multi-band $s_{++}$ superconductivity in ${\text{V}}_3\text{Si}$ determined from the response to a controlled disorder
• Impurity-induced bound states inside the superconducting gap of FeSe
• Influence of disorder on the signature of pseudogap and multigap superconducting behavior in FeSe
• Complete electrodynamics of a BCS superconductor with $\mu$eV energy scales: microwave spectroscopy on titanium at mK temperatures
• Relationships between Superconductivity and Nematicity in FeSe${}_{1-x}$Te${}_x$ ($x=0-0.5$) Films Studied by Complex Conductivity Measurements
• Effect of disorder on the competition between nematic and superconducting order in FeSe
• Superconductivity of highly spin-polarized electrons in FeSe probed by ${}^{77}$Se NMR
• Electronic States and Energy Dissipations of Vortex Core in Pure FeSe Single Crystals Investigated by Microwave Surface Impedance Measurements
• Studies of superconductivity of Fe chalcogenides in films grown by PLD technique