Spinless fermions in a $\mathbb{Z}_{2}$ gauge theory on the triangular ladder

TL;DR

This paper investigates spinless fermions coupled to a $ ext{Z}_2$ gauge theory on a triangular ladder, revealing how geometry and boundary conditions influence confinement, phase transitions, and quantum phases, with detailed numerical analysis.

Contribution

It extends the analysis of $ ext{Z}_2$ gauge theories to a triangular ladder geometry, highlighting the effects of lattice structure and boundary conditions on phase behavior and transitions.

Findings

Deconfinement-confinement crossover influenced by boundary conditions

Existence of a quantum phase transition into a confined fermionic dimer gas

Identification of competing flux insulator and flux metal phases

Abstract

A study of spinless matter fermions coupled to a constrained $\mathbb{Z}_{2}$ lattice gauge theory on a triangular ladder is presented. The triangular unit cell and the ladder geometry strongly modify the physics, as compared to previous analysis on the square lattice. In the static case, the even and odd gauge theories for the empty and filled ladder are identical. The gauge field dynamics due to the electric coupling is drastically influenced by the absence of periodic boundary conditions, rendering the deconfinement-confinement process a crossover in general and a quantum phase transition (QPT) only for decorated couplings. At finite doping and in the static case, a staggered flux insulator at half filling and vanishing magnetic energy competes with a uniform flux metal at elevated magnetic energy. As for the square lattice, a single QPT into a confined fermionic dimer gas is found versus electric coupling. Dimer resonances in the confined phase are however a second order process only, likely reducing the tendency to phase separate for large magnetic energy. The results obtained employ a mapping to a pure spin model of $\mathbb{Z}_{2}$ gauge-invariant moments, adapted from the square lattice, and density matrix renormalization group calculations thereof for numerical purposes. Global scans of the quantum phases in the intermediate coupling regime are provided.