Electronic specific-heat anomalies in high-Tc cuprates

In this work, we study the electronic specific heat Ce(T ) of underdoped to overdoped high-Tc cuprates, and identify the nature of anomalies in Ce(T ) at the superconducting transition temperature Tc and at temperatures above Tc. The doped cuprate superconductor is considered as a multi-carrier model system which is composed of different types of charge carriers. The normal-state electronic specific heat Cn(T ) of high-Tc cuprates below a characteristic pseudogap (PG) temperature 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 Cn(T ) coming from the unpaired intrinsic and extrinsic polarons are calculated within the two-component degenerate Fermi-gas model. The total electronic specific heat Ce(T ) = Cn(T ) + Cs(T ) below Tc is calculated by considering the contribution Cn(T ) and the contribution Cs(T ) coming from the superfluid bosonic carriers. We have shown that our theoretical predictions of the behaviors of Ce(T ) near Tc and above Tc are strikingly similar to the behaviors of the electronic specific heat observed below and above Tc in LSCO and YBCO. There is fair quantitative agreement between theoretical predictions about the anomalies in Ce(T ) (i.e. a λ-like anomaly near Tc and a BCS-type anomaly above Tc near T ∗) and experimental data.