Low Temperature Specific Heat of the Underdoped La_2-xSr_xCuO₄ Single Crystals

We report the low-temperature specific heat of La_2-xSr_xCuO₄ (x = 0.063) single crystals before and after annealing in the temperature region of 2-10 K and magnetic fields up to 12 T. The data confirm the √H dependence of the linear term coefficient γ predicted for d-wave paring in the Volovik theory at T = 0 K. However, the data do not satisfy the proposed Simon-Lee scaling law at finite temperatures, i.e., C_DOS/(T²) = f(T/√H), where f is an unknown scaling function and C_DOS is the extra specific heat contributed by the nodal quasiparticles due to the Doppler effect. Possible reasons for this failure are presented.