Superconducting Properties of Pd_{1- x}Pt _xBi₂over a Wide Pressure Range

The topological insulator, PdBi2, exhibits two different crystal phases (i.e., α-PdBi2 and β-PdBi2) at ambient pressure. Here, we prepared new superconducting materials, Pd1-xPtxBi2, via Pt doping of PdBi2 and investigated their superconducting properties. Pt doping of PdBi2 may be anticipated to show higher superconducting transition temperature Tc than pure PdBi2 because of the example that Pt doping of PdTe2 (Tc = 2.0 K) leads to higher Tc (Tc = 3.2 K for Pd0.25Pt0.75Te2) via reconstruction of Fermi surface topology. The Pd1-xPtxBi2 samples prepared in this study contained both the α and β phases, as seen in the XRD patterns. The x dependence of Tc was investigated for Pd1-xPtxBi2; the highest Tc value (4.35 K) was observed at x = 0.12, which was probably due to the β phase. In this study, the crystal structure and superconducting transition temperature of Pd0.88(6)Pt0.12(6)Bi2.2(2) are fully investigated over a wide pressure (p) range. Both α phase and β phase remain up to a pressure of approximately 20 GPa; however, the amount of the α phase gradually decreased with an increase in pressure. The pressure dependence of unit cell volume V of the α and β phases resulted in smooth shrinkage of the lattice. The temperature (T) dependence of the electrical resistance (R) at different pressures showed enhancement of Tc of the α phase with pressure and almost constant Tc in the β phase, with a trend that is similar to that of α-PdBi2 and β-PdBi2. The temperature dependence of the upper critical field at 10.5 GPa suggested that it deviates from the simple s-wave dirty/clean limit model and follows the p-wave polar model, which causes the topologically nontrivial nature of superconductivity.