Two characteristic contributions to the superconducting state of 2$H$-NbSe$_2$

TL;DR

This study investigates multiband superconductivity in 2H-NbSe2 by analyzing vortex lattice structures, revealing two distinct superconducting bands with different gap magnitudes and a moderate interband coupling.

Contribution

It provides detailed field- and temperature-dependent data confirming two superconducting bands in 2H-NbSe2 and characterizes their gap sizes and coupling.

Findings

Two distinct superconducting gaps identified

One band’s contribution suppressed above 0.8 T

Moderate interband coupling inferred

Abstract

Multiband superconductivity arises when multiple electronic bands contribute to the formation of the superconducting state, allowing distinct pairing interactions and gap structures. Here, we present field- and temperature-dependent data on the vortex lattice structure in 2$H$-NbSe$_2$ as a contribution to the ongoing debate on the nature of the superconductivity in this material. The field-dependent data clearly show that there are two distinct superconducting bands, and the contribution of one of them to the vortex lattice signal is completely suppressed for magnetic fields above $\sim$ 0.8 T, well below $B\mathrm{_{c2}}$. By combining the temperature and field scans, we can deduce that there is a moderate degree of interband coupling. From the observed temperature dependences, we find that at low field and zero temperature, the two gaps in temperature units are 13.1 $\pm$ 0.2 and 6.5 $\pm$ 0.3 K ($\Delta_{0}$ = 1.88 and 0.94 $k\mathrm{_{B}} T\mathrm{_{c}} $); the band with the larger gap gives just under two-thirds of the superfluid density. The penetration depth extrapolated to zero field and zero temperature is 160 $\pm$ 2 nm.