The Hall-Lorenz number in the La1.855Sr0.145CuO4 single crystal

The temperature dependence of the Hall-Lorenz number (Lxy) for the optimally doped La1.855Sr0.145CuO4 (LSCO) has been obtained from the experimentally determined transverse and longitudinal transport coefficients. A comparison between Lxy(T) dependence found for LSCO and Lxy(T) reported previously for copper indicates that the Hall-Lorenz number in LSCO follows standard metallic behavior from room temperature down to T∼150K. Below this temperature the Lxy coefficient deviates from regular metallic dependence in a way characteristic of an electronic system with lowered density of electronic states at the Fermi level. We present results of calculations provided in terms of the Boltzmann equation for a two-dimensional model of the electronic structure with a d-symmetrical pseudogap. A temperature Tmax, where a maximum in the Lxy(T) dependence appears, turns out to be dependent on the width of the supposed pseudogap (Egmax). The best agreement between the model and the experimental data was obtained for Egmax∼25meV, which corresponds well with values reported previously by other groups.