Competing pseudogap and impurity effects on the normal-state specific heat properties of cuprate superconductors

In this paper, we show that the pseudogap in the excitation spectra of high- T c cuprates together with the impurity phase and charge inhomogeneity plays key roles in determining the essential features of their anomalous specific heat properties observed above T c . We consider the doped cuprate superconductor as a multi-carrier model system (which consists of intrinsic and extrinsic polarons and pre-formed bosonic Cooper pairs) and study the competing pseudogap and impurity effects on the normal-state electronic specific heat of high- T c cuprates taking into account charge inhomogeneities. We argue that unconventional electron–phonon interactions are responsible for the precursor Cooper pairing in the polaronic band below a mean-field temperature T ∗ and the existence of a pseudogap above T c in the cuprates. The electronic specific heat C e ( T ) of doped cuprates below T ∗ is calculated taking into account three contributions coming from the excited components of Cooper pairs, the ideal Bose-gas of incoherent Cooper pairs and the unpaired carriers in the impurity band. Above T ∗ , two contributions to C e ( T ) coming from the unpaired intrinsic and extrinsic polarons are calculated within the two-component degenerate Fermi-gas model. By comparing our results with the experimental C e ( T ) data obtained for La- and Y-based cuprates, we find that the observed behaviors of C e ( T ) (below and above T ∗ ) are similar to the calculated results for C e ( T ) and the BCS-type jumps of C e ( T ) at T ∗ may be depressed by the impurity effects and may become more or less pronounced BCS-type anomalies in C e ( T ) .