Pressure dependence of the electrical properties of GaBi solidified in low gravity

Immiscible GaBi alloys were solidified during free fall in the NASA Marshall Space Flight Center drop tower, which provides about 4.5 seconds of low gravity. The electrical resistivity and magnetic susceptibility were measured as a function of pressure (up to 18 kbar) and temperature (300 K to 4.2 K) of drop tower (DT) and ground control (GC) samples prepared under identical conditions, except for gravity. At ambient pressure the electrical resistance of the DT sample exhibits a broad maximum at 100 K, while that of GC sample decreases rapidly as temperature decreases. Both DT and GC samples become superconducting at 7.7 K. However, a minor second superconducting phase with a transition temperature at 8.3 K is observed only in the DT samples.