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

P. Wróbela,c, A. Maciąga, R. Ederb, P. Fuldec and R. Micnasd aInstitute for Low Temperature and Structure Research, P.O. Box 1410, 50-950 Wrocław 2, Poland bForschungszentrum Karlsruhe, IFP, P.O. Box 3640, 76021 Karlsruhe, Germany cMax Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany dAdam Mickiewicz University, Institute of Physics, Umultowska 85, 61-614 Poznań, Poland

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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.

DOI: 10.12693/APhysPolA.106.575 PACS numbers: 74.20.Mn, 71.10.Fd