Ultrasonic study of the spin-Peierls systemCuGeO3under pressure

Abstract

We present the temperature dependence of the acoustic sound velocity for a ${\mathrm{CuGeO}}_{3}$ single crystal measured under pressure up to 10 kbar. Anomalous elastic behavior along the $c$ axis, observed around 100 K, is accounted for by the existence of a magnetoelastic coupling. We show that this coupling is weakly affected by pressure. Moreover, the temperature dependence of the sound velocity below the spin-Peierls phase transition is analyzed using a Landau-type model from which we obtain the temperature and pressure dependences of the order parameter. We find that the magnetic spin-Peierls energy gap increases with pressure at a rate of $d\ensuremath{\Delta}/dP=0.11\ifmmode\pm\else\textpm\fi{}0.01$ meV/kbar.