Ultrasonic evidence of a spin-Peierls transition inα′-NaV2O5

Abstract

We report the anomalous behavior of the ${C}_{22}$ elastic constant in ${\ensuremath{\alpha}}^{\ensuremath{'}}$-NaV${}_{2}$O${}_{5}$ by studying the propagation of longitudinal ultrasonic waves along the chain direction. A stiffening anomaly is clearly seen at 35 K, which could be the signature of a spin-Peierls transition. The results are discussed and compared with the temperature dependence of the analogous elastic constant ${(C}_{33})$ in the ${\mathrm{CuGeO}}_{3}$ system. Magnetic-field effects have also been investigated. Anomalously small shifts of the transition temperature are observed.