Superconductor-insulator transition in fcc GeS b2 T e4 at elevated pressures

We show that polycrystalline GeSb2Te4 in the fcc phase (f-GST), which is an insulator at low temperature at ambient pressure, becomes a superconductor at elevated pressures. Our study of the superconductor-insulator transition versus pressure at low temperatures reveals a second-order quantum phase transition with linear dependence of the transition temperature on the pressure above the critical zero-Temperature pressure. In addition, we demonstrate that at higher pressures the f-GST goes through a structural phase transition via amorphization to bcc GST (b-GST), which also becomes superconducting. We also find that in the pressure regime where an inhomogeneous mixture of amorphous and b-GST exists, there is an anomalous peak in magnetoresistance, and we suggest an explanation for this anomaly.