Arguments and evidence for a node-containing anisotropic s-wave gap form in the cuprate superconductors

Abstract

Although not widely recognized, there is much evidence suggesting that the superconducting cuprates have an anisotropic s-wave type of gap form, a form which is usually so highly anisotropic that it contains gap nodes and regions of opposite sign. This evidence is presented and reviewed. This evidence motivates a search for s-wave explanations of the many experiments which seem to require the d-wave gap form. s- wave explanations are presented here for three of the phase-sensitive Josephson tunnelling experiments, experiments which are widely regarded as some of the most convincing evidence for the x2−y2 d-wave gap form. A key feature in all of these explanations is orthorhombicity. Although the evidence and reinterpretations of phase-sensitive experiments clearly improve the credibility of the anisotropic-s gap form, some important issues are still unsettled and the question of the gap form remains open. An experimental test is proposed.

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