Spiral magnetism and chiral superconductivity in Kondo-Hubbard triangular lattice model

TL;DR

This paper investigates the phase diagram of a Kondo-Hubbard triangular lattice model, revealing spiral magnetic order, Kondo singlet phases, and $d+id$ superconductivity, with competition and coexistence between magnetism and superconductivity.

Contribution

It introduces a detailed phase diagram for the Kondo-Hubbard triangular lattice, including spiral magnetic order, Kondo singlet, and $d+id$ superconductivity, using the variational cluster approximation.

Findings

Spiral magnetic order dominates at small $J_{ot}$ and moderate $U$.

Kondo singlet phase is stable at large $J_{ot}$.

Superconductivity with $d+id$ symmetry appears at finite doping, coexisting with spiral magnetism.

Abstract

Building on the results of Ref. \cite{faye2018phase}, which identified an antiferromagnetic and Kondo singlet phases on the Kondo-Hubbard square lattice, we use the variational cluster approximation (VCA) to investigate the competition between these phases on a two-dimensional triangular lattice with $120^{o}$ spin orientation. In addition to the antiferromagnetic exchange interaction $J_{\perp}$ between the localized (impurity) and conduction (itinerant) electrons, our model includes the local repulsion $U$ of the conduction electrons and the Heisenberg interaction $J_H$ between the impurities. At half-filling, we obtain the quantum phase diagrams in both planes $(J_{\perp}, U J_{\perp})$ and $(J_{\perp}, J_{H})$. We identify a long-range, three-sublattice, spiral magnetic order which dominates the phase diagrams for small $J_{\perp}$ and moderate $U$, while a Kondo singlet phase becomes more stable at large $J_{\perp}$. The transition from the spiral magnetic order to the Kondo singlet phase is a second-order phase transition. In the $(J_{\perp}, J_{H})$ plane, we observe that the effect of $J_H$ is to reduce the Kondo singlet phase, giving more room to the spiral magnetic order phase. It also introduces some small magnetic oscillations of the spiral magnetic order parameter. At finite doping and when spiral magnetism is ignored, we find superconductivity with symmetry order parameter $d+id$, which breaks time reversal symmetry. The superconducting order parameter has a dome centered at around $5\%$ hole doping, and its amplitude decreases with increasing $J_{\perp}$. We show that spiral magnetism can coexist with $d+id$ state and that superconductivity is suppressed, indicating that these two phases are in competition.