Mixed singlet‐triplet superconducting state in doped antiferromagnets

Abstract

We analyze symmetry mixing in the superconducting (SC) order parameter of planar cuprates. The behavior of thermal conductivity observed in some systems doped with magnetic impurities or in some systems exposed to external magnetic field seems to indicate that such symmetry mixing takes place. We discuss this phenomenon in the framework of the spin polaron model (SPM). We assume that antiferromagnetic (AF) correlations, which are at least of short range, tend to confine motion of holes which have been created in the AF spin background. The nature of the propagation of quasiparticles which are hole-like and the nature of the interaction between quasiparticles is determined by a tendency to restore the local AF order. It is known that two holes in the t -J model (tJM) form bound states with d x 2 -y 2 or p-wave symmetry. The d-wave bound state has lower energy and is the ground state. The mixing of d-wave symmetry with p-wave symmetry takes place in the SC order parameter at some range of finite values of the doping parameter. That range lies at the applicability verge of the SPM, where AF correlation are already very short. On the other hand, these correlations may be strengthened by above mentioned external factors, which seems to explain why symmetry mixing is observed in this case.

Spin Polaron-Bipolaron Scenario of Three Gap-Like Energy Scales in Superconducting Cuprates

“…Recently, it has been announced that in multilayered heterogeneous oxide structures it is possible to induce a triplet component in a cuprate superconductor [54]. The proximity to the stabilization of a superconducting state with a p-wave component has been also predicted in the framework of the spin polaron approach [55].…”

Spin fluctuations and the "strange metal" behavior of a weakly doped antiferromagnet

“…[ 15] It was assumed that the hopping takes place between the NNN and next NNN sites, and the superconducting hole-hole attraction is due to the minimization of the energy of the system, when two holes occupy nearest sites. In this case, the minimal number of the antiferromagnetic bonds is broken [ 17,18,19,20,21] and similarly to the Hubbard and the tJ-model cases, the pairing takes places predominantly in the d-wave channel [ 21].…”

“…Such a comparison is also necessary to the phenomenological parameters for the spin fluctuation correlation function Eq. (20). The frequency ω is given in units of 1/(2m * ξ 2 ).…”

“…It was assumed that the hopping takes place between the NNN and next NNN sites, and the superconducting hole-hole attraction is due to the minimization of the energy of the system, when two holes occupy the nearest sites. In this case, the minimal number of antiferromagnetic bonds is broken [19][20][21][22][23] and similarly to the Hubbard and the tJ-model cases, the pairing takes places predominantly in the d-wave channel [23]. It is important to stress that in order to explain the maximum of the quasi-particle spectrum at k = (±π/2, ±π/2), one has to neglect the NN hopping, t = 0, despite the fact that this hopping matrix element is larger than the other hopping parameters.…”