  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 quasi-linearly from room temperature down to 60 K, then
undergoes a two-step metal-to-insulator transitions (MIT) at temperatures T1 =
59.4 K and T2 = 58.7 K which may be related to a structural phase transition or
occurrence of charge density wave ordering. Upon applying pressure, the
two-step (T1, T2) MIT splits into three steps (T1, T2 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.
