Low temperature specific heat anomaly in electron doped R2-xCexCuO4 superconductors

Abstract

The electron doped rare earth copper oxide superconductors R 2-x Ce x CuO 4 exhibit anomalous heavy fermion behavior at low temperature with large Sommerfeld specific heat coefficient which is different from the conventional heavy fermion systems. The system is described by a model Hamiltonian consisting of staggered magnetic field in the two sub-lattices of the copper sites in presence of hybridization between the localized 4f electrons of Nd atom and the conduction electrons as well as the f-electron kinetic energy term. The Hamiltonian is solved by Zubarev's Green's function technique and the sub-lattice magnetization is calculated and solved self-consistently. The entropy and specific heat are calculated from the free energy of the system. The temperature dependent entropy and specific heat are numerically evaluated by successive differentiations of sub-lattice magnetization and temperature dependent entropy. It is observed that when the position of the f-level of Nd atom is of the order of hybridization strength, the sub-lattice magnetization is destroyed drastically at lower temperatures. As a result, the specific heat exhibits a large enhancement at low temperatures suggesting the enhancement of the electron density of states and the effective mass of the itinerant electrons exhibiting the heavy fermion character. Similarly, the specific heat shows anomalously sharp jump near the Néel temperature.