Specific heat studies in Ho-Ba-CuO superconductors: Fermionic and bosonic contributions

The specific heats of superconducting HoBa 2Cu3O7-δ ( T c ≅ 92 K) have been theoretically investi- gated in the temperature domain 70 ≤ T ≤ 110 K. The bosonic (phonons) contribution to the specific heat is estimated from Debye model in the harmonic approximation for high temperature expansion ( T > θD/2π) using the moments of the phonon density of states. The fermionic constituent as the electronic specific heat is deduced using a suitable trial function above and below Tc. As a next step the contribution of specific heat by charge oscillations (plasmons) are obtained. The theoretical results from bosonic and fermionic terms are then com- pared with the experimental results. We find that the specific heats from electronic as well as plasmon term are only a fraction of lattice specific heat and in particular, plasmons do not influence the thermal conduction signi- ficantly. The implications of the above analysis are discussed.