Unconventional Superconductivity, Spontaneous Time-Reversal Symmetry Breaking and Lowering of Kinetic Energy in Doped, Short-Range Antiferromagnets

Abstract

In this paper we focus on the anomalous temperature dependence of the in-plane conductivity and symmetry mixing of the superconducting order parameter observed in various experiments on cuprates. We show that the one-band Hubbard model is not capable of describing the physics of cuprates because the kinetic energy is lowered in this model in the superconducting state, which contradicts experimental observations. The proper model to investigate doped, short--range antiferromagnets is the t−J model, for which our results agree with experiments. We analyze a spin polaron model, that is an effective model for a doped antiferromagnet. In the framework of this model we also study the superconducting order-parameter symmetry-mixing phenomenon. We show that the expected mixing of d-wave symmetry with p-wave symmetry takes place in the superconducting order-parameter at a finite value of the doping parameter. This symmetry mixing brakes the time-reversal symmetry.

Asymmetric Tunneling Conductance in Doped Antiferromagnets

“…Figure 1 depicts both the normalized conductance through NIN junction for the temperature T = 0.05t, where t ∼ 0.5eV , when both sides of the junction are in the normal state, and the normalized conductance through the NIS junction for the temperature T = 0.005t, when the right side is in the SC state. In the latter case we use superconducting gap values obtained for the respective ground state calculated in the previous paper [8]. The asymmetry of DOS can be easily seen in Fig.…”

“…In the framework of the SPM we will derive the conductance formula for the metal-metal (NIN) junction and the metal-superconductor (NIS) junction. The derivation of the spin polaron Hamiltonian on which our calculation relies on can be found in our previous paper [8].…”