Superconductivity in the t- t′- J model

Abstract

Superconducting transition temperature T c is determined for the two-dimensional t- t′- J model. Here t( t′) is the hopping integral between nearest-neighbor (NN) and next-NN (NNN) sites, respectively; J is the antiferromagnetic interaction between NN sites. Two techniques are used for finding the extended s- and d-wave T c , i.e., the mean-field X-operator technique (MFXOT) and the Gutzwiller approximation (GA). First, as for the pure t- J model, the both methods give qualitatively different results. It is argued that the MFXOT yields more physical predictions than the GA, especially close to half-filling. Second, it is demonstrated that t′ has strong influence on the values of the extended s-wave T c (in both approximations used). With the MFXOT, the obtained s-wave values of T c are in close agreement with those found in the high-temperature superconducting oxides.