Comparison of the normal state properties of $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ and its deuterated analogue in high magnetic fields and under high hydrostatic pressures

TL;DR

This study compares the Fermi-surface topology of deuterated and undeuterated ${eta}$-(BEDT-TTF)$_2$Cu(NCS)$_2$ under pressure, revealing isotope effects linked to changes in electronic structure affecting superconductivity.

Contribution

It provides the first detailed comparison of Fermi-surface topology changes in deuterated and undeuterated salts under pressure, explaining the negative isotope effect.

Findings

Superconducting transition temperature drops more rapidly in deuterated salt with pressure.

Fermi-surface topology changes occur more quickly in deuterated salt under pressure.

Isotope substitution causes small differences in Fermi-surface topology, influencing superconductivity.

Abstract

Details of the Fermi-surface topology of deuterated $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ ~have been measured as a function of pressure, and compared with equivalent measurements of the undeuterated salt. We find that the superconducting transition temperature is much more dramatically suppressed by increasing pressure in the deuterated salt. It is suggested that this is linked to pressure-induced changes in the Fermi-surface topology, which occur more rapidly in the deuterated salt than in the undeuterated salt as the pressure is raised. Our data suggest that the negative isotope effect observed on deuteration is due to small differences in Fermi-surface topology caused by the isotopic substitution.