Optimal inhomogeneity for superconductivity: Finite-size studies

Wei-Feng Tsai; Hong Yao; Andreas Läuchli; Steven A. Kivelson

doi:10.1103/PhysRevB.77.214502

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Optimal inhomogeneity for superconductivity: Finite-size studies

Wei-Feng Tsai, Hong Yao, Andreas Läuchli, Steven A. Kivelson

DOI 10.1103/PhysRevB.77.214502 · Physical Review B

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Abstract

We report the results of exact-diagonalization studies of Hubbard models on a 4×4 square lattice with periodic boundary conditions and various degrees and patterns of inhomogeneity, which are represented by inequivalent hopping integrals t and t′. We focus primarily on two patterns, the checkerboard and the striped cases, for a large range of values of the on-site repulsion U and doped hole concentration x. We present evidence that superconductivity is strongest for U of the order of the bandwidth and intermediate inhomogeneity 0<t′<t. The maximum value of the “pair-binding energy” we have found with purely repulsive interactions is Δpb=0.32t for the checkerboard Hubbard model with U=8t and t′=0.5t. Moreover, for near-optimal values, our results are insensitive to changes in boundary conditions, suggesting that the correlation length is sufficiently short that finite-size effects are already unimportant.