Elastic softening in single-crystalline La2−xSrxCuO4 around x =⅛

Ultrasonic velocity variations in La 2– x Sr x CuO 4 single crystals

“…The variations are very much alike those reported in ref. [3][4][5] for similar Sr concentrations. Going from high temperature down to low temperature, we first see a hardening for both polarizations, which becomes a softening for the T 1 wave but stays a monotonous increase for T 2 .…”

“…Again we measured analogous variations to those reported in ref. [3,5]. It is clearly shown too that the magnetic field enhanced widely the low temperature relaxation-like variations.…”

“…[3] and [5]. The limited extent of data for the uppertemperature range does not allow to further decompose the in-plane measurements and to separate for this polarization the ph-ph contribution from the transition-like variations.…”

“…This effect has been best seen in La 2-x Ba x CuO 4 where around this particular concentration a second structural transition appears between the orthorhombic at midtemperatures (OMT) and a tetragonal phase at low temperature (TLT) (see ref. 1 of [5]). This transition leads to a sharp decrease of T c .…”

“…The TLT structure has not been observed in LSCO but the decrease has been. Therefore, Sakita et al [5] tentatively explain the anomalous variations by the interplay between the superconducting gap formation and the TLT structural transition which should be of Peierls type. More specifically, the superconducting-gap formation would stop the structural instability and would lead to the hardening of the elastic constant.…”