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arXiv:cond-mat/0212256 · Physical review. B, Condensed matter

Optimal inhomogeneity for superconductivity

Enrico Arrigoni, Steven Allan Kivelson

Published Nov 14, 2003• 36 citations
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Abstract

We study the effect of nonuniform transverse couplings on a quasi-one-dimensional superconductor. We show that inhomogeneous couplings quite generally increase the superconducting (pairing) gap relative to the uniform system, but that beyond an ``optimal'' degree of inhomogeneity, they lead to a suppression of the tendency towards phase coherence. The optimal conditions for superconductivity are derived. We also show that a delocalized, spin-gapped phase is stable against weak disorder in a four-leg ladder with moderate repulsive interactions.

DOI
10.1103/physrevb.68.180503

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The Hubbard model provides a simple framework in which one can study how certain aspects of the electronic structure of strongly interacting systems can be tuned to optimize the superconducting pairing correlations and how these changes affect the mechanisms giving rise to them. Here we use a weak-coupling random phase approximation to study a two-dimensional Hubbard model with a unidirectional modulation of the hopping amplitudes as the system evolves from the uniform square lattice to an array of weakly coupled two-leg ladders. We find that the pairing correlations retain their dominant ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wavelike structure and that they are significantly enhanced for a slightly modulated lattice. This enhancement is traced backed to an increase in the strength of the spin-fluctuation pairing interaction due to favorable Fermi surface nesting in the modulated system. We then use a random-phase approximation BCS framework to examine the evolution of the neutron resonance in the superconducting state. We find that it changes only weakly for moderate modulations, but breaks up into two distinct resonances at incommensurate wave vectors in the limit of weakly coupled ladders.
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