Low-energy excitations in 2-leg and 3-leg quantum spin ladders

TL;DR

This paper investigates low-energy excitations in 2-leg and 3-leg quantum spin ladders using bosonization and gauge theory, revealing distinct excitation modes and predicting a phase transition with an energy gap upon inter-ladder interaction.

Contribution

It provides a detailed theoretical analysis of low-energy excitations in spin ladders, highlighting the role of zero modes and predicting a phase transition induced by inter-ladder coupling.

Findings

2-leg system described by spin triplet Majorana fermions

3-leg system characterized by two massless scalar fields

Inter-ladder interaction leads to a phase transition and energy gap

Abstract

Low-energy excitations in spin 1/2 antiferromagnetic Heisenberg spin ladders are studied by bosonization and gauge theoretical description. It is explicitly shown that zero modes in the bosonization play an essentially important role. Low-energy excitations in the 2-leg system is described by spin triplet Majorana fermions, and in the 3-leg case spin excitations on the top and bottom ladders are described by two massless scalar fields. It is predicted that if inter-ladder interaction between the top and bottom chains is introduced, a phase transition occures at some critical coupling and the system acquires an energy gap.