Penetration depth study of superconducting gap structure of 2\textit{H}-NbSe$_2$

TL;DR

This study investigates the anisotropic superconducting gap structure of 2H-NbSe2 by measuring penetration depths at very low temperatures, revealing a reduced energy gap on specific Fermi surface sheets, challenging previous assumptions.

Contribution

It provides new insights into the gap structure of 2H-NbSe2, showing the reduced gap resides on Nb Fermi surfaces rather than Se sheets, informing microscopic models of its superconductivity.

Findings

Reduced energy gap on Nb Fermi surface sheets

Contrasts with previous reports on Se sheet gaps

Implications for models of anisotropic superconductivity

Abstract

We report measurements of the temperature dependence of both in-plane and out-of-plane penetration depths ($\lambda_a$ and $\lambda_c$ respectively) in 2\textit{H}-NbSe$_2$. Measurements were made with a radio-frequency tunnel diode oscillator circuit at temperatures down to 100 mK. Analysis of the anisotropic superfluid density shows that a reduced energy gap is located on one or more of the quasi-two-dimensional Nb Fermi surface sheets rather than on the Se sheet, in contrast to some previous reports. This result suggests that the gap structure is not simply related to the weak electron-phonon coupling on the Se sheet and is therefore important for microscopic models of anisotropic superconductivity in this compound.