Acoustic anomalies in the resonant ultrasound spectra of La2-x SrxCuO4

Resonant ultrasound spectroscopy is a novel technique for the simultaneous determination of a solid's elastic moduli. Measurements of the resonant ultrasound spectra of single crystals of La2-xSrxCuO4 for several values of x are reported. Anomalies associated with the nonstoichiometric (x>0) doped superconductor have been observed. These anomalies indicate that the absence of short-wavelength translational invariance at the Brillouin-zone edge is being coupled into the zone center. Measurements of the stoichiometric (x=0) insulator will also be discussed. [This work was performed at Los Alamos National Laboratory under the auspices of the U.S. Department of Energy.]