Substitution Effect by Deuterated Donors on Superconductivity in κ-(BEDT-TTF)2Cu[N(CN)2]Br
We investigate the superconductivity in the deuterated BEDT-TTF molecular substitution system κ-[(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 accurately control chemical pressure near the Mott boundary, which results in the modification of the superconductivity. After cooling slowly, an increase in T c observed up to x ∼0.1 is evidently caused by the chemical pressure effect. Neither a reduction of T c nor a suppression of superconducting volume fraction is found below x ∼0.5. This demonstrates that the effect of disorder by substitution is negligible in the present system. With further increase in x , both T c and superconducting volume fraction start to decrease toward values at x = 1.