Pressure Phase Diagram of the Organic Superconductor β-(BEDT-TTF)₂I₃

Abstract

Low temperature phase diagram of β-(BEDT-TTF) 2 I 3 as a function of pressure ( P ) is determined by resistivity measurement. The superconducting transition temperature ( T c ) rises from 1.1–1.5 K ( P =0 kbar) to around 7.4 K ( P =1.3 kbar) and decreases to 1.2 K ( P =7 kbar). We propose that two kinds of superconducting states exist in this salt and that ambient pressure gives two stable states which have T c 's of around 8 K as well as around 1.3 K. The upper critical field, H c2 , along the c * -axis is also presented.