Scanning tunneling spectroscopy of superconducting LiFeAs single crystals: Evidence for two nodeless energy gaps and coupling to a bosonic mode

TL;DR

This study uses scanning tunneling spectroscopy on LiFeAs single crystals to identify two nodeless superconducting gaps and evidence of coupling to a bosonic mode, aligning surface and bulk properties.

Contribution

It provides the first detailed spectroscopic evidence of two nodeless gaps and their temperature dependence in LiFeAs, linking surface measurements to bulk superconductivity.

Findings

Two nodeless gaps of 5.3 and 2.5 meV were observed.

Gaps close at the bulk $T_c$, indicating surface-bulk consistency.

A dip-hump structure suggests coupling to a bosonic mode.

Abstract

The superconducting compound, LiFeAs, is studied by scanning tunneling microscopy and spectroscopy. A gap map of the unreconstructed surface indicates a high degree of homogeneity in this system. Spectra at 2 K show two nodeless superconducting gaps with $\Delta_1=5.3\pm0.1$ meV and $\Delta_2=2.5\pm0.2$ meV. The gaps close as the temperature is increased to the bulk $T_c$ indicating that the surface accurately represents the bulk. A dip-hump structure is observed below $T_c$ with an energy scale consistent with a magnetic resonance recently reported by inelastic neutron scattering.