Anomalous hypersonic behavior ofCuGeO3prior to the spin-Peierls transition

Abstract

The temperature dependence of the longitudinal elastic constants c 22 , c 33 , and of the transverse elastic constant c 44 , as obtained by Brillouin spectroscopy, reveals an unexpected elastic behavior in CuGeO 3 prior to the spin-Peierls magnetic transition (T SP Ϸ14.1 K). At room temperature c 33 ӷc 44 Ͼc 22 . Below about 50 K a steep increase in the values of the longitudinal elastic constants leads to a crossover of the values of c 22 and c 44 with c 22 Ͼc 44 . The existence of translation-rotation coupling in CuGeO 3 could account for the elastic behavior above T SP . The anisotropy of the magnetoelastic coupling at the spin-Peierls transition temperature is reflected in the different temperature behavior