Superconducting pairing and density-wave instabilities in quasi-one-dimensional conductors

TL;DR

This paper uses a renormalization group approach to map the phase diagram of quasi-one-dimensional conductors, revealing conditions for various superconducting and density-wave phases, and explaining experimental observations in Bechgaard salts.

Contribution

It provides a detailed theoretical analysis of phase competition in quasi-1D conductors, including the effects of interchain interactions and nesting deviations, and connects these to experimental phenomena.

Findings

d-wave superconductivity dominates at large nesting deviations

Triplet f-wave phase emerges with weak interchain backscattering

Proximity of SDW, CDW, and superconducting phases explains experimental puzzles

Abstract

Using a renormalization group approach, we determine the phase diagram of an extended quasi-one-dimensional electron gas model that includes interchain hopping, nesting deviations and both intrachain and interchain repulsive interactions. d-wave superconductivity, which dominates over the spin-density-wave (SDW) phase at large nesting deviations, becomes unstable to the benefit of a triplet $f$-wave phase for a weak repulsive interchain backscattering term $g_1^\perp>0$, despite the persistence of dominant SDW correlations in the normal state. Antiferromagnetism becomes unstable against the formation of a charge-density-wave state when $g_1^\perp$ exceeds some critical value. While these features persist when both Umklapp processes and interchain forward scattering ($g_2^\perp$) are taken into account, the effect of $g_2^\perp$ alone is found to frustrate nearest-neighbor interchain $d$- and $f$-wave pairing and instead favor next-nearest-neighbor interchain singlet or triplet pairing. We argue that the close proximity of SDW and charge-density-wave phases, singlet d-wave and triplet $f$-wave superconducting phases in the theoretical phase diagram provides a possible explanation for recent puzzling experimental findings in the Bechgaard salts, including the coexistence of SDW and charge-density-wave phases and the possibility of a triplet pairing in the superconducting phase.