Physical Review Research (Jul 2020)

Discovery of a low-temperature orthorhombic phase of the Cd_{2}Re_{2}O_{7} superconductor

  • Konrad J. Kapcia,
  • Maureen Reedyk,
  • Mojtaba Hajialamdari,
  • Andrzej Ptok,
  • Przemysław Piekarz,
  • Armin Schulz,
  • Fereidoon S. Razavi,
  • Reinhard K. Kremer,
  • Andrzej M. Oleś

DOI
https://doi.org/10.1103/PhysRevResearch.2.033108
Journal volume & issue
Vol. 2, no. 3
p. 033108

Abstract

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The favorable combination of Raman spectroscopy of the lattice vibrations with ab initio phonon calculations enables us to pinpoint a low-temperature orthorhombic phase which hosts the cryptic 1 K superconducting phase of the 5d pyrochlore-type superconductor Cd_{2}Re_{2}O_{7}. Raman studies are performed on crystals with the natural isotope abundance and cadmium and oxygen isotope enriched samples. Characteristic splitting and the appearance of sharp phonon modes in the temperature-dependent Raman spectra prove a structural phase below ∼80 K, induced by a soft-mode phonon instability of the intermediate-temperature tetragonal crystal structure. The theory predicts that this low-temperature orthorhombic crystal structure is described by the space group F222; it exhibits no phonon instabilities and has the lowest total energy. Future experiments on the F222 phase should establish whether spin-triplet components contribute to the superconducting phase.