Gauge Theory Description of Spin Ladders

TL;DR

This paper models spin ladders using gauge theory, revealing how inter-chain interactions induce a finite energy gap and how ladder systems' gap properties depend on the number of legs, connecting condensed matter physics with gauge theories.

Contribution

It introduces a gauge theory framework to describe spin ladders, providing new insights into the gap formation and parity effects in multi-leg systems.

Findings

Inter-chain interactions induce a finite energy gap in two-leg ladders.

The energy gap is approximately 0.25 times the inter-chain coupling for small J'.

N-leg ladders are gapless for odd N and gapped for even N.

Abstract

A s=1/2 antiferromagnetic spin chain is equivalent to the two-flavor massless Schwinger model in an uniform background charge density in the strong coupling. The gapless mode of the spin chain is represented by a massless boson of the Schwinger model. In a two-leg spin ladder system the massless boson aquires a finite mass due to inter-chain interactions. The gap energy is found to be about .25 k |J'| when the inter-chain Heisenberg coupling J' is small compared with the intra-chain Heisenberg coupling. k is a constant of O(1). It is also shown that a cyclically symmetric N-leg ladder system is gapless or gapful for an odd or even N, respectively.