Analysis of nonlinear conductivity of point contacts on the base of FeSe in the normal and superconducting state

TL;DR

This study investigates the nonlinear electrical conductivity of FeSe point contacts, revealing surface degradation effects, superconducting features, and two-gap structures, advancing understanding of FeSe's electronic properties in normal and superconducting states.

Contribution

It provides new insights into the nonlinear conductivity and superconducting gap features of FeSe point contacts, highlighting surface degradation effects and identifying two distinct superconducting gaps.

Findings

Superconducting features appear in low-resistance point contacts.

Two superconducting gaps of 2.5 and 3.5 meV were identified.

Surface degradation significantly influences the conductivity measurements.

Abstract

Nonlinear conductivity of point contacts (PCs) on the base of FeSe single crystals has been investigated. Measured dV/dI dependencies demonstrate the prevailing contribution to the PC conductivity caused by the degraded surface. Superconducting (SC) feature in dV/dI like a sharp zero-bias minimum develops for relatively low ohmic PCs, where the deep areas of FeSe are involved. Analysis of dV/dI has shown that the origin of the zero-bias minimum is connected with the Maxwell part of the PC resistance, what masks energy dependent spectral peculiarities. Even so, we have found the specific features in dV/dI - the sharp side maxima, which may have connection to the SC gap, since their position follows the BCS temperature dependence. Exploring the dV/dI spectra of the rare occurrence with Andreev-like structure, the two gaps with Delta = 2.5 and 3.5 meV were identified.