No abstract

We have measured the thermal conductivity in the ab-plane (κ ab) as well as the c-axis (κ c) of a series of underdoped La 2−x Sr x CuO 4 (LSCO) single crystals grown by the travelling-solvent floating-zone (TSFZ) method. It was found that temperature dependence of thermal conductivity exhibits an interesting feature: there exists a steplike drop of thermal conductivity below ∼10 K in both κ ab (T) and κ c (T), and this drop in thermal conductivity occurs at lower temperature with lower Sr concentration. Furthermore, it is found that the magnitude of this drop at x = 0.11 and 0.125 is larger than at other doping levels. We suspect that this phenomenon is due to an LTO (low-temperature orthorhombic) to short-range (local) or dynamical LTT-like (low-temperature tetragonal) structure transition.