Thermal Transport in Undoped Cuprate La₂CuO₄

We report high-resolution measurements of the thermal conductivity κ_xx and thermal Hall conductivity κ_xy in the undoped cuprate La₂CuO₄ in magnetic fields B (normal to the CuO2 plane) up to 13 T at temperatures 2.5 to 16 K. For the longitudinal thermal conductivity κ_xx, we detect a weak cuspy anomaly that implies either a structural or magnetic transition at ~6 K. The critical temperature is independent of B up to 13 T. In addition, we detect at all temperatures up to 10 K hysteretic loops centered near B = ± 5 T in the field profiles of κ_xx. Comparison of our data with earlier results by Thio, Birgeneau et al. shows that the hysteretic loops are continuation of similar hysteretic loops detected at 150 and 200 K [1]. In the thermal Hall channel, we have not observed any finite value in κ_xy (or in the thermal resistivity λ_yx) at temperatures between 2.5 and 12 K. By regulating the sample temperature to a stability range of σ_T/T = ~0.002% to ~0.02% depending on temperature, and incrementing B in steps of 0.2 T over a 5 hour sweep, we can detect Δλ_yx = ~ 2 ×10^-4 K m/W. Our upper bound for (Δκ_xy /T < ~ 0.1 mW K^-2 m^-1) is roughly 20X smaller than that in an earlier report. We have also searched without success for a finite K_xy using the technique of cooling in a fixed B.

[1] Thio, Tineke, et al. "Antisymmetric exchange and its influence on the magnetic structure and conductivity of La₂CuO₄." Physical Review B 38.1 (1988): 905.