Anomalies in low-temperature thermal conductivity of underdopedLa2−xSrxCuO4 single crystals

Abstract

We have measured the thermal conductivity in theab-plane(κab) as well asthe c-axis(κc) of a series ofunderdoped La2−xSrxCuO4 (LSCO) single crystals grown by the travelling-solvent floating-zone (TSFZ) method.It was found that temperature dependence of thermal conductivity exhibits aninteresting feature: there exists a steplike drop of thermal conductivity below∼10 K inboth κab(T) and κc(T), and this drop in thermal conductivity occurs at lower temperature with lowerSr concentration. Furthermore, it is found that the magnitude of this drop atx = 0.11 and 0.125 is larger than at other doping levels. We suspect that this phenomenon is due toan LTO (low-temperature orthorhombic) to short-range (local) or dynamical LTT-like(low-temperature tetragonal) structure transition.