Abstract
Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a "dip-hump" feature at energy Ω∼4.7kBTc beyond the superconducting gap Δ. Spectra on strained regions of the FeSe films reveal simultaneous decreases in Δ and Ω. This contrasts with all previous reports on other high-Tc superconductors, where Δ locally anticorrelates with Ω. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors.
Highlights
In support of this hypothesis, inelastic neutron scattering experiments have revealed a spin resonance at the nesting wave vector connecting the Γ-centered hole pockets to the M-centered electron pockets in iron pnictides [4,5,6], as well as FeSe0.4Te0.6 [7]
The density of states (DOS) reconstruction can be probed by the differential tunneling conductance dI=dV, in which the features of the bosonic mode often appear at energies ÆðΔ þ ΩÞ, where Δ is the superconducting gap energy and Ω is the energy of the bosonic mode
For cuprates and the more recently discovered iron pnictides, measurements with scanning tunneling microscopy and spectroscopy (STM/STS) revealed dip-hump structures at energies above Δ, which have been controversially interpreted as fingerprints of phonon or spin fluctuations [16,17,18,19,20,21,22,23]
Summary
“Imaging the Electron-Boson Coupling in Superconducting FeSe Films Using a Scanning Tunneling Microscope.” Physical Review Letters 112 (5) (February): 057002. Imaging the Electron-Boson Coupling in Superconducting FeSe Films Using a Scanning Tunneling Microscope Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films.
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