Superconductivity in ternary pnictide SrPd₂Sb₂ polymorphs

Superconductivity was observed in SrPd₂Sb₂ polymorphs: a primitive tetragonal CaBe₂Ge₂-type (low-temperature phase, LT-SrPd₂Sb₂) structure and body-centered ThCr₂Si₂-type (high-temperature phase, HT-SrPd₂Sb₂) structure. The superconducting transition was observed at T_c = 1.95 (LT) and 0.6 K (HT). The specific heat C(T) showed a clear anomaly at T_c = 1.85 (LT) and 0.6 K (HT); thus, the superconductivity was of a bulk nature. The agreement with the Bardeen–Cooper–Schrieffer (BCS) curve indicated that the LT-SrPd₂Sb₂ superconductor was fully gapped. The values of electron–phonon coupling λ_ep and density of state at Fermi level N(E_F) in 122 compounds with the CaBe₂Ge₂-type and its related structure were evaluated to reveal the main factor that determines T_c. From our systematic analysis, T_c of this family can be explained by λ_ep rather than N(E_F). (author)