Pair-density-wave phase of strongly interacting electrons on the triangular lattice: A variational Monte Carlo study

TL;DR

This study uses variational Monte Carlo simulations to investigate the pair density wave phases in a triangular lattice $t$-$J$-$V$ model, revealing s-wave and d-wave PDWs with symmetry breaking and valley-polarization effects.

Contribution

It provides the first large-scale variational Monte Carlo analysis of PDW phases in the $t$-$J$-$V$ model on a triangular lattice, identifying new pairing states and symmetry-breaking mechanisms.

Findings

Low-density favors s-wave PDW ground state.

Intermediate densities show nematic d-wave PDW.

PDW formation linked to valley polarization and intra-pocket pairing.

Abstract

A robust theory of the mechanism of pair density wave (PDW) superconductivity (i.e. where Cooper pairs have nonzero center of mass momentum) remains elusive. Here we explore the triangular lattice $t$-$J$-$V$ model, a low-energy effective theory derived from the strong-coupling limit of the Holstein-Hubbard model, by large-scale variational Monte Carlo simulations. When the electron density is sufficiently low, the favored ground state is an s-wave PDW, consistent with results obtained from previous studies in this limit. Additionally, a PDW ground state with nematic d-wave pairing emerges in the intermediate range of electron densities and phonon frequencies. For these s-wave and d-wave PDWs arising in states with spontaneous breaking of time-reversal and inversion symmetries, PDW formation derives from valley-polarization and intra-pocket pairing.