2005/03/31 by C. A. Kendziora, I. A. Sergienko, R. Jin +4
Physics and Astronomy · #cond-mat.mtrl-sci #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevlett.95.125503
published as Phys. Rev. Lett. 95, 125503 (2005) · 4+ pages, 4 figures. Updated figures and text. Accepted to PRL
arxiv created 2005/08/03 · arxiv updated 2009/12/01
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.