Substitution Effect by Deuterated Donors on Superconductivity in $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br

TL;DR

This study explores how deuterated molecular substitution in a superconductor affects its critical temperature and volume fraction, revealing that chemical pressure influences superconductivity without significant disorder effects.

Contribution

It demonstrates that deuterated substitution can finely tune chemical pressure near the Mott boundary, affecting superconductivity without introducing notable disorder.

Findings

$T_c$ increases up to $x \\sim 0.1$ due to chemical pressure.

No significant $T_c$ reduction below $x \\sim 0.5$, indicating negligible disorder effects.

Both $T_c$ and superconducting volume decrease at higher $x$ values.

Abstract

We investigate the superconductivity in the deuterated BEDT-TTF molecular substitution system $\kappa$-[(h8-BEDT-TTF)$_{1-x}$(d8-BEDT-TTF)$_x$]$_2$Cu[N(CN)$_2$]Br, where h8 and d8 denote fully hydrogenated and deuterated molecules, respectively. Systematic and wide range ($x$ = 0 -- 1) substitution can control chemical pressure finely near the Mott boundary, which results in the modification of the superconductivity. After cooling slowly, the increase of $T_{\textrm{c}}$ observed up to $x \sim$ 0.1 is evidently caused by the chemical pressure effect. Neither reduction of $T_{\textrm{c}}$ nor suppression of superconducting volume fraction is found below $x \sim$ 0.5. This demonstrates that the effect of disorder by substitution is negligible in the present system. With further increase of $x$, both $T_{\textrm{c}}$ and superconducting volume fraction start to decrease toward the values in $x$ = 1.