Mixed spin ladders with exotic ground states

TL;DR

This paper investigates mixed spin ladder systems with S=1 and S=1/2 spins, revealing exact ground states and exotic phases induced by frustration, including highly degenerate singlet states and simple models with nontrivial ground states.

Contribution

It introduces exactly solvable models of mixed spin ladders with exotic and highly degenerate ground states, expanding understanding of frustrated quantum spin systems.

Findings

Exact ground states found for certain mixed spin ladder models.

Strong frustration induces exotic, highly degenerate singlet ground states.

Simple models with nontrivial ground states, including bilinear exchange, are identified.

Abstract

We study the "mixed spin" isotropic ladder system having S=1 spins on one leg and S=1/2 spins on the other, with general-type exchange interactions between spins on neighboring rungs. A set of model Hamiltonians with exact ground states in the form of a certain matrix product wave function is obtained. We show that sufficiently strong frustration can lead to exotic singlet ground states with infinite (exponential) degeneracy. We also list a couple of rather simple models with nontrivial ground states, including a model with only bilinear exchange.