Hole pairing and ground state properties of high-T c superconductivity within the t–t′–J–V model

The t–t′–J–V model, one of the realistic models for studying high-T c cuprates, has been investigated to explore the hole pairing and other ground state properties using exact diagonalization (ED) technique with 2 holes in a small 8-site cluster. The role of next-nearest-neighbor (NNN) hopping and nearest-neighbor (NN) Coulomb repulsion has been considered. It appears that qualitative behavior of the ground state energies of an 8-site and 16- or 18-site cluster is similar. Results show that a small short-ranged antiferromagnetic (AF) correlation exists in the 2 hole case which is favored by large V∕t. A superconducting phase emerges at 0 ≤ V∕t ≤ 4J. Hole–hole correlation calculation also suggests that the two holes of the pair are either at |i − j| = 1 or √2. Negative t′∕t suppresses the possibility of pairing of holes. Though s-wave pairing susceptibility is dominant, pairing correlation length calculation indicates that the long range pairing, which is suitable for superconductivity, is in the d-wave channel. Both s- and d-wave pairing susceptibility gets suppressed by V∕t while d-(s-) wave susceptibility gets favored (suppressed) by t′∕t. The charge gap shows a gapped behavior while a spin-gapless region exists at small V∕t for finite t ′ ∕t.