Chemical Doping and High-Pressure Studies of Layered β-PdBi₂ Single Crystals

We have systematically grown large single crystals of the layered compounds β-PdBi₂, and both the hole-doped PdBi₂₋ₓPb₂ and the electron-doped NaₓPdBi₂, and studied their magnetic and transport properties. Hall effect measurements on PdBi₂, PdBi₁₈Pb₀₂, and Na₀.₀₅₇PdBi₂ show that the charge transport is dominated by electrons in all of the samples. The electron concentration is substantially reduced upon Pb doping in PdBi₂₋ₓPbₓ and increased upon Na intercalation in NaₓPdBi₂, indicating effective hole doping by Pb and electron doping by Na. We observed a monotonic decrease of the superconducting transition temperature (T_c) from 5.4 K in undoped PdBi₂ to less than 2 K for x > 0.35 in hole-doped PdBi₂₋ₓPbₓ. Meanwhile, a rapid decrease of T_c with Na intercalation is also observed in the electron-doped NaₓPdBi₂, which is in disagreement with the theoretical expectation. In addition, both the magnetoresistance and Hall resistance further reveal evidence for a possible spin excitation associated with Fermi surface reconstruction at ∼50 K in the Na-intercalated PdBi₂ sample. The complete phase diagram is thus established from hole doping to electron doping. Meanwhile, a high-pressure study of the undoped PdBi₂ shows that the T_c is linearly suppressed under pressure with a dT_c/dP coefficient of -0.28 K/GPa.