Goldstone-Mode Phonon Dynamics in the Pyrochlore Cd2Re2O7

Abstract

We have measured the polarized Raman scattering spectra of Cd2Re2O7, the first superconducting pyrochlore, as a function of temperature. For temperatures below the cubic-to-tetragonal structural phase transition (SPT) at 200K, a peak with B1 symmetry develops at zero frequency with divergent intensity. We identify this peak as the first observation of the Goldstone phonon in a crystalline solid. The Goldstone phonon is a collective excitation that exists due to the breaking of the continuous symmetry with the SPT. Its emergence coincides with that of a Raman-active soft mode. The order parameter for both features derives from an unstable doubly-degenerate vibration (with Eu symmetry) of the O1 atoms which drives the SPT.

4+ pages, 4 figures. Updated figures and text. Accepted to PRL

References in corpus (9)

• Superconductivity at 1 K in Cd2Re2O7
• Observation of a Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet
• Polarized Raman study of the phonon dynamics in Pb(Mg${}_{1/3}$Nb)O${}_3$ crystal
• Superconductivity in the Correlated Pyrochlore Cd_2Re_2O_7
• Metallic "Ferroelectricity" in the Pyrochlore Cd2Re2O7
• Low Temperature Symmetry of Pyrochlore Oxide Cd2Re2O7
• Structural Ordering and Symmetry Breaking in Cd_2Re_2O_7
• Structural Order Parameter in the Pyrochlore Superconductor Cd2Re2O7
• Fluctuation Effects on the Physical Properties of Cd2Re2O7 Near 200 K

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