Field and temperature dependences of the specific heat of the La1.85Sr0.15CuO4 superconductor

Abstract

This paper reports on the temperature and field dependences of the specific heat of high-quality La1.85Sr0.15CuO4 single crystals carried out at low temperatures in magnetic fields of up to 8 T for two magnetic field orientations, namely, along the [100] and [110] crystallographic axes. The field dependence of the electronic density of states (DOS) was found to be anisotropic for different magnetic field orientations in the a–b plane, with the electronic density being the lowest along the a axis (for H ∥ [100]) and maximum for the field inclined at 45° to the a axis (for H ∥ [110]). Electronic specific heat in a magnetic field was observed to depend linearly on temperature T and nonlinearly on the magnetic field H: CDOS=bTH1/2. In a zero field, the electronic specific heat grows quadratically with temperature as CDOS=αT2. Estimation of the maximum superconducting gap width from the experimentally determined values of the α coefficient of T2 and of the electronic DOS in the normal state yields Δ 0=300 K. The observed features indicate that La1.85Sr0.15CuO4 is a superconductor with d symmetry of the order parameter.