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 $X$Pd${}_2$Sn ($X$ = Ti, Zr, Hf), by means of electrical transport, magnetic susceptibility, specific heat and x-ray diffraction measurements. TiPd${}_2$Sn, ZrPd${}_2$Sn and HfPd${}_2$Sn undergo structural phase transitions from the room-temperature cubic MnCu${}_2$Al-type structure (space group $Fm\bar{3}m$) 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 ZrPd${}_2$Sn demonstrate the emergence of a superstructure with multiple commensurate modulations below $T_s$. ZrPd${}_2$Sn and HfPd${}_2$Sn have bulk superconductivity (SC) with transition temperatures $T_c$ $\sim$ 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 $X$Pd${}_2$Sn systems are good candidates for examining the interplay between CDW and SC.

10 pages, 8 figures

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