Negative thermal expansion near two structural quantum phase transitions

ORAL

Abstract

We present an inelastic X-ray scattering study of the structural phase transitions and thermal expansion (TE) behavior of the mercurous halides (Hg2X2 with X=Br,I). The body-centered tetragonal (BCT) to orthorhombic transition at Tc = 150K in Hg2Br2 is induced by the freezing of the transverse acoustic phonon at the X-point in the BCT Brillouin zone, as we confirm by the soft-mode behavior and static structure factor. For the case X = I, the X mode does not freeze but softens considerably, extrapolating to Tc = -22K which implies that mercurous iodide at low temperatures is situated very close to a structural quantum phase transition (SQPT). While Hg2Br2 displays normal TE, we report for the first time that low temperature Hg2I2 reveals significant negative TE behavior on the approach to the SQPT below T = 70K. We contextualize this result against the 3d-transition metal trifluorides, in particular ScF3 which is another system that displays negative TE above an incipient structural transition.

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Presenters

  • Connor Occhialini

    Department of Physics, University of Connecticut, University of Connecticut

Authors

  • Connor Occhialini

    Department of Physics, University of Connecticut, University of Connecticut

  • Sahan Handunkanda

    Department of Physics, University of Connecticut, Univ of Connecticut - Storrs

  • Ayman Said

    Advanced Light Source, Argonne National Laboratory, Advanced Photon Source, Argonne National Laboratory

  • Sudhir Trivedi

    Brimrose Corporation, Brimrose Technology Corporation

  • Gian Guzman-Verri

    Materials Science Division, Argonne National Laboratory, Argonne National Laboratory

  • Jason Hancock

    Department of Physics and Institute of Material Science, University of Connecticut, Univ of Connecticut - Storrs, Department of Physics, University of Connecticut, University of Connecticut