d-wave superconductivity near charge instabilities

TL;DR

This paper explores how charge instabilities near phase separation or charge-density-wave transitions promote d-wave superconductivity in high-temperature superconductors, emphasizing the role of singular interactions and quantum criticality.

Contribution

It demonstrates that charge instabilities induce a strongly q-dependent interaction favoring d-wave pairing, providing a theoretical framework consistent with high-Tc superconductor phase diagrams.

Findings

D-wave pairing is strongly favored near charge instabilities.

Superconducting temperature depends on proximity to quantum critical points.

The phase diagram aligns with properties of high-temperature superconductors.

Abstract

We investigate the symmetry of the superconducting order parameter in the proximity of a phase-separation or of an incommensurate charge-density-wave instability. The attractive effective interaction at small or intermediate transferred momenta is singular near the instability. This strongly $q$-dependent interaction, together with a residual local repulsion between the quasiparticles and an enhanced density of states for band structures appropriate for the high temperature superconducting oxides, strongly favors the formation of $d$-wave superconductivity. The relative stability with respect to superconductivity in the $s$-wave channel is discussed in detail, finding this latter hardly realized in the above conditions. The superconducting temperature is mostly determined by the closeness to the quantum critical point associated to the charge instability and displays a stronger dependence on doping with respect to the simple proximity to a Van Hove singularity. The relevance of this scenario and the generic agreement of the resulting phase diagram with the properties displayed by high temperature superconducting oxides is discussed.