Superconductor-to-insulator transition of lambda-BETS2FexGa1-xCl4

The lambda-type BETS alloys (BETS=bis(ethylenedithio)tetrathiaful valene), lambda-BETS2FexGal-xCl4 exhibited an unprecedented superconduct or-to-insul ator (SC-I) transition around x=0.43 at ambient pressure. The large suscept ibility drop at T-C and its recovery at T-SC.I clearly show this SC-I trans ition reflects an intrinsic property of the crystals. The anisotropic field dependence of magnetization at 2 K indicated the insulating ground state t o be antiferromagnetic. lambda-BETS2FexGa1-xCl4 undergoes a MI transition a t x>x(cl) (approximate to 0.5), SC transition at x<x(c2) (approximate to 0. 35) and SC-I transition at x(c2)<x<x(cl). The SC-I transition was also obse rved in lambda-BETS2FexGa1-xCl4 (x=0.55) at 1 kbar, which exhibited a metal -insulator (MI) transition at ambient pressure. At high pressure, the SC ph ase was observed up to x=0.9. The SC-to-M transition was also observed at h igh pressure in the Br-containing system, lambda-BETS2FeyGa1-yBrxCl4-x.