Effective models of doped quantum ladders of non-Abelian anyons

Abstract

Quantum spin models have been studied extensively in one and higher dimensions. Furthermore, these systems have been doped with holes to study $t$--$J$ models of $SU(2)$ spin-1/2. Their anyonic counterparts can be built from non-Abelian anyons, such as Fibonacci anyons described by $SU(2)_3$ theories, which are quantum deformations of the $SU(2)$ algebra. Inspired by the physics of $SU(2)$ spins, several works have explored ladders of Fibonacci anyons and also one-dimensional (1D) $t$--$J$ models. Here we aim to explore the combined effects of extended dimensionality and doping by studying ladders composed of coupled chains of interacting itinerant Fibonacci anyons. We show analytically that in the limit of strong rung couplings these models can be mapped onto effective 1D models. These effective models can either be gapped models of hole pairs, or gapless models described by $t$--$J$ (or modified $t$--$J$--$V$) chains of Fibonacci anyons, whose spectrum exhibits a fractionalization into charge and anyon degrees of freedom. By using exact diagonalizations for two-leg and three-leg ladders, we show that indeed the doped ladders show exactly the same behavior as that of $t$--$J$ chains. In the strong ferromagnetic rung limit, we can obtain a new model that hosts two different kinds of Fibonacci particles - which we denote as the heavy $\tau$'s and light $\tau$'s. These two particle types carry the same (non-Abelian) topological charge but different (Abelian) electric charges. Once again, we map the two-dimensional ladder onto an effective chain carrying these heavy and light $\tau$'s. We perform a finite size scaling analysis to show the appearance of gapless modes for certain anyon densities whereas a topological gapped phase is suggested for another density regime.