Suppression of metal-to-insulator transition and stabilization of superconductivity by pressure in Re3Ge7

The effect of pressure on the low-temperature states of the Re₃Ge₇ is investigated by both electrical and Hall resistance and magnetization measurements. At ambient pressure, the temperature-dependent resistance of Re₃Ge₇ behaves quasilinearly from room temperature down to 60 K, then undergoes a two-step metal-to-insulator transition (MIT) at temperatures T₁=59.40.16em0exK and T₂=58.70.16em0exK, which may be related to a structural phase transition or occurrence of charge-density wave ordering. Upon applying pressure, the two-step (T₁,0.16em0exT₂) MIT splits into three steps (T₁,0.16em0exT₂. and T₃) above 1 GPa, and all traces of MITs are fully suppressed by {~}8 GPa. Subsequently, the onset of bulk superconductivity (SC) occurs between 10.8 and 12.2 GPa and persists to our highest pressure of 26.8 GPa. At 12.2 GPa the superconducting transition temperature, Tc, and upper critical field, Hc2 reach the maximum of Tc (onset) {~}5.9 K and Hc2 (1.8 K) {~}14 kOe. Our results not only present the observation of SC under high pressure in Re₃Ge₇ but also delineate the interplay between SC and other competing electronic states by creating a T-p phase diagram for this potentially topologically nontrivial system Re₃Ge₇.