Superconductor-to-insulator transition of λ-BETS2FexGa1 − xCl4

The λ-type BETS alloys (BETS=bis(ethylenedithio)tetrathiafulvalene), λ-BETS2FexGa1 − xCl4 exhibited an unprecedented superconductor-to-insulator (SC-I) transition around x = 0.43 at ambient pressure. The large susceptibility drop at Tc and its recovery at tsc-i clearly show this SC-I transition reflects an intrinsic property of the crystals. The anisotropic field dependence of magnetization at 2 K indicated the insulating ground state to be antiferromagnetic. λ-BET2FexGa1 − xCl4 undergoes a MI transition at x>xc1 (≈0.5), SC transition at x<xc2 (≈0.35) and SC-I transition at xc2<x<xc1. The SC-I transition was also observedin λ-BETS2FexGa1 − xCl4 (x ≈0.55) at 1 kbar, which exhibited a metal-insulator (MI) transition at ambient pressure. At high pressure, the SC phase was observed up to x≈0.9. The SC-to-M transition was also observed at high pressure in the Brcontaining system, λ-BETS2FeyGa1 − yBrxCl4 − x.