Investigation of LiFeAs by means of "Break-junction" Technique

TL;DR

This study uses the break-junction technique to investigate the superconducting gaps in LiFeAs, revealing two distinct gaps and their relation to the critical temperature, contributing to understanding multiband superconductivity.

Contribution

The paper presents a novel tunneling investigation of LiFeAs using the break-junction method, identifying two superconducting gaps and their characteristics.

Findings

Large gap $ ightarrow$ 2.5-3.4 meV

Small gap $ ightarrow$ 0.9-1 meV

BCS ratio for large gap $ ightarrow$ 4.6-5.6

Abstract

In our tunneling investigation using Andreev superconductor - normal metal - superconductor contacts on LiFeAs single crystals we observed two reproducible independent subharmonic gap structures at dynamic conductance characteristics. From these results, we can derive the energy of the large superconducting gap $\Delta_L=(2.5 \div 3.4)$ meV and the small gap $\Delta_L=(0.9 \div 1)$ meV at $T = 4.2$ K for the $T_C^{local} \approx (10.5 \div 14)$ K (the contact area critical temperature which deviation causes the variation of $\Delta_L$). The BCS-ratio is found to be $2\Delta_L/k_BT_C = (4.6 \div 5.6)$, whereas $2\Delta_S/k_BT_C \ll 3.52$ results from induced superconductivity in the bands with the small gap.