α- and β-(BEDT-TTF)2I3 - two modifications with contrasting groundstate properties: insulator and volume superconductor

Abstract

The α-modification of (BEDT-TTF)2I3 undergoes a metal-to-insulator transition at T = 135 K. Application of hydrostatic pressure shifts the transition temperature to lower values. Above 12 kbar semimetallic behavior is observed, but no superconductivity is detected up to a pressure of 17 kbar and temperatures down to l00 mK. The β-modifcation, on the other hand, exhibits ambient pressure volume superconductivity below Tc = 1.05 K. Measurements of the anisotropy of the diamagnetic shielding- as well as the Meissner-magnetization are presented.