Structural phase transitions and superconductivity in the Heusler intermetallics $X$Pd$_2$Sn ($X$ = Ti, Zr, Hf)

Abstract

We report the discovery of structural phase transitions and superconductivity in the full Heusler compounds XPd2Sn (X = Ti, Zr, Hf), by means of electrical transport, magnetic susceptibility, specific heat and x-ray diffraction measurements. TiPd2Sn, ZrPd2Sn and HfPd2Sn undergo structural phase transitions from the room-temperature cubic MnCu2Al-type structure (space group F m 3m) to a low-temperature tetragonal structure at around 160 K, 110 K and 90 K, respectively, which are likely related charge density wave (CDW) instabilities. Low temperature single crystal x-ray diffraction measurements of ZrPd2Sn demonstrate the emergence of a superstructure with multiple commensurate modulations below Ts. ZrPd2Sn and HfPd2Sn have bulk superconductivity (SC) with transition temperatures Tc ∼ 1.2 K and 1.3 K, respectively. Density functional theory (DFT) calculations reveal evidence for structural and electronic instabilities which can give rise to CDW formation, suggesting that these XPd2Sn systems are good candidates for examining the interplay between CDW and SC.