Low-temperature specific heat of La1.85Sr0.15CuO4 and La2CuO4

The specific heat of polycrystalline samples of the high-Tc superconductor La1.85Sr0.15CuO4 and the undoped insulator La2CuO4 have been measured from 80 mK to 4 K and from 7 to 55 K. The low-temperature limit of the specific heat of La1.85Sr0.15CuO4 can be well accounted for by a sizable linear T term (γT) in addition to the Debye-like term (BT3) with γ=1.8±0.2 mJ/K2 mol. A contribution due to possible magnetic impurities is also present. In contrast, the coefficient of the linear T term in La2CuO4 is found to be 0.2±0.2 mJ/K2 mol. The large linear T term in the superconducting sample suggests the presence of the Fermi-liquid-type excitations at low temperatures.