Arguments and evidence for a node-containing anisotropics-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 x 2 Ϫy 2 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.

Pairing interactions and pairing mechanism in high-temperature copper oxide superconductors

“…This pairing mechanism contradicts the very recent ARPES data, which show that multiple phonon modes at 27 meV, 45 meV, 61 meV, and 75 meV are strongly coupled to doped holes in deeply underdoped La 2−x Sr x CuO 4 20 . The strong coupling to the multiple phonon modes is not in favor of d-wave gap symmetry but may support a general s-wave gap symmetry 26,27 . Here we determine the polaron binding energy E p for undoped parent cuprates from the unconventional oxygen-isotope effect on the antiferromagnetic ordering temperature (T N ) 5 .…”

Superconductivity from Repulsion: Ginzburg–Landau Phenomenology of Cuprates

“…A competition of screened Coulomb pairing repulsion and phonon-mediated attraction or AF magnonmediated repulsion determines [32] observed unconventional symmetry of the SC order parameter in cuprates [35,36].…”

dc Josephson Current Between an Isotropic and a d-Wave or Extended s-Wave Partially Gapped Charge Density Wave Superconductor

“…However, conventional s-wave contributions were also detected in electron tunneling experiments [153][154][155][156][157][158][159][160] and, probably, in nuclear magnetic resonance (NMR) and nuclear quadrupole resonance measurements [161]. Therefore, only a minority of researchers prefer to accept the isotropic s-wave (or extended s-wave) nature of superconductivity in cuprates [162][163][164][165][166][167][168][169][170][171][172][173][174][175]. Notwithstanding the existing fundamental controversies, the d-wave specificity of high-T c oxide superconductivity has already been used in technical devices [95,116,[118][119][120]122].…”