Ground-state phases of rung-alternated spin-1/2 Heisenberg ladder

TL;DR

This study explores the diverse ground-state phases of a rung-alternated spin-1/2 Heisenberg ladder, revealing ferrimagnetic, dimerized, and topologically ordered states through analytical and numerical methods.

Contribution

It provides a comprehensive phase diagram for the ladder model, identifying new ferrimagnetic and topological phases depending on exchange interactions.

Findings

Ferrimagnetic ground state for ferromagnetic leg exchanges

Multiple ground states including dimerized and topological phases for antiferromagnetic exchanges

Discovery of a ferrimagnetic Luttinger liquid phase with unique dispersions

Abstract

The ground-state phase diagram of Heisenberg spin-1/2 system on a two-leg ladder with rung alternation is studied by combining analytical approaches with numerical simulations. For the case of ferromagnetic leg exchanges a unique ferrimagnetic ground state emerges, whereas for the case of antiferromagnetic leg exchanges several different ground states are stabilized depending on the ratio between exchanges along legs and rungs. For the more general case of a honeycomb-ladder model for the case of ferromagnetic leg exchanges besides usual rung-singlet and saturated ferromagnetic states we obtain a ferrimagnetic Luttinger liquid phase with both linear and quadratic low energy dispersions and ground state magnetization continuously changing with system parameters. For the case of antiferromagnetic exchanges along legs, different dimerized states including states with additional topological order are suggested to be realized.