Unconventional superconductivity on the triangular lattice Hubbard model

TL;DR

This study uses advanced quantum Monte Carlo simulations to reveal unconventional chiral d+id superconductivity driven by spin fluctuations in the hole-doped Hubbard model on a triangular lattice, relevant to several real materials.

Contribution

It demonstrates the emergence of a doubly degenerate singlet pairing state mediated by antiferromagnetic spin fluctuations, providing new insights into superconductivity in frustrated systems.

Findings

Identification of a doubly degenerate singlet pairing state.

Spin fluctuations along the $ ext{Γ}$-$ ext{K}$ direction mediate pairing.

Support for chiral d+id superconductivity in related materials.

Abstract

Using large-scale dynamical cluster quantum Monte Carlo simulations, we explore the unconventional superconductivity in the hole-doped Hubbard model on the triangular lattice. Due to the interplay of electronic correlations, geometric frustration, and Fermi surface topology, we find a doubly degenerate singlet pairing state at an interaction strength close to the bare bandwidth. Such an unconventional superconducting state is mediated by antiferromagnetic spin fluctuations along the $\Gamma$-$K$ direction, where the Fermi surface is nested. An exact decomposition of the irreducible particle-particle vertex further confirms the dominant component of the effective pairing interaction comes from the spin channel. Our findings provide support for chiral $d +i d$ superconductivity in water-intercalated sodium cobaltates Na$_{x}$CoO$_{2} \cdot y$H$_{2}$O, as well as insight into the superconducting phases of the organic compounds $\kappa$-(ET)$_{2}$X and Pd(dmit)$_{2}$.