Pressure induced effects on the Fermi surface of superconducting 2H-NbSe$_2$

TL;DR

This study investigates how applying pressure up to 19 GPa affects the superconducting properties and Fermi surface of 2H-NbSe$_2$, revealing a peak in electron-phonon coupling at 5 GPa and a maximum critical temperature at 10.5 GPa.

Contribution

It demonstrates the pressure-induced evolution of the Fermi surface and superconducting parameters, highlighting differences from other compounds with competing ground states.

Findings

Electron-phonon coupling peaks at 5 GPa.

Critical temperature T_c reaches maximum at 10.5 GPa.

Fermi surface changes correlate with superconducting behavior.

Abstract

The pressure dependence of the critical temperature $T_c$ and upper critical field $H_{c2}(T)$ has been measured up to 19 GPa in the layered superconducting material 2H-NbSe$_2$. Relating the behavior of $H_{c2}(T)$ to Fermi surface parameters, we find that the electron phonon coupling of the 2D Nb 4d derived bands shows a peak at 5 GPa when the charge density wave (CDW) order is suppressed. On the other hand, $T_c(P)$ shows a bell shaped curve with a maximum at 10.5 GPa, well above the pressure for the suppression of the CDW order. Changes in the band structure produce this shift in the maximum of $T_c(P)$, demonstrating that 2H-NbSe$_2$ shows important differences with respect to other compounds where $T_c$ has a maximum in the temperature-density phase diagram shaped by the suppression of another, non-superconducting, ground state.