Elasticity studies ofLa2−xSrxCuO4

Abstract

We report measurements of Young’s modulus Y and internal friction δ of the high-$T_c$ superconductor ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$. For x=0.15, anomalies in Y and δ at $T_c$=40 K are preceded by a dramatic decrease in Y, indicative of a soft phonon mode beginning near 200 K. For x=0.30, the softening is absent. The magnetic field dependence of Y and δ is investigated, and predictions are made for Δ$C_p$ and ∂$H_{c2}$/∂T.