Analysis of experimental heat capacity of HoBa2Cu3O7–δ: electron heat capacity and phonon spectrum characteristics

The electron component γT of heat capacity was derived from the experimental data on the heat capacity of HoBa2Cu3O7–δ in the normal state (above Tc). The heat capacity was divided into phonon and electron components by using a special technique based on the representation of lattice heat capacity in terms of a finite number of moments Θi of the phonon density of states. Apart from the value of γ, numerical values of the second moment Θ2, the fourth moment Θ4, and the effective moment Θ* characterizing the upper limit of the phonon density of states were also obtained. In comparison to the phonon spectrum of YBCO, the phonon spectrum of HoBCO is in general softer due to the replacement of the lighter Y ion by the heavier Ho ion. Such a softening of the phonon density of states makes it possible to separate the electron heat capacity in HoBa2Cu3 O7–δ in the superconducting transition region, as well as the heat capacity jump ΔC.