Study of Low Temperature Specific Heat in La-Ba/Sr-CuO Superconductors

Abstract

The low temperature specific heat of La 1.85 Ba 0.15 CuO 4 and La 1.8 Sr 0.2 CuO 4 superconductors has been investigated based on the free electron, layered electron gas model of quasi-two-dimensional (2D) layers of CuO 2 along the a-b plane. The interaction potential properly incorporates the effect of electron-electron, electron-phonon and electron-plasmon interactions. The lattice contribution to the specific heat is well estimated from the electron-phonon part of the interaction potential. The results on the behaviour of the specific heat (C) with temperature (T) for both systems are similar to those observed in previous experiments. It is noticed that the specific heat contribution from the Debye model is significant at low temperatures (5 K ≤ T ≤ T c ) while the Einstein model affords the specific heat at higher temperatures (T ≥ T c ). The estimated lattice specific heat, when subtracted from the experimental data, results in a finite value of the electronic specific heat coefficient (γ). Non-zero values of γ indicate the electronic origin intrinsic to these superconductors. A linear temperature dependence of ΔC (= C exp - C latt )/T in the range 20 K ≤ T ≤ 45 K is depicted. Furthermore, the density of states at the Fermi level is also estimated. The results derived are consistent with the reported data. The implications of the above analysis are discussed.