Low-lying excitations of the three-leg spin tube using the density-matrix renormalization group method

TL;DR

This study uses the density-matrix renormalization group method to analyze low-energy excitations in a three-leg antiferromagnetic Heisenberg model, revealing how symmetry and coupling modulations influence the spin gap and spectral features.

Contribution

It provides detailed numerical analysis of the spin gap and dynamical structure factors, highlighting the effects of asymmetric intra-ring coupling modulations on low-lying excitations.

Findings

Spin excitations are always gapped with regular triangular intra-ring couplings.

Small asymmetric modulations collapse the spin gap.

Inter-leg spectral features are highly sensitive to coupling asymmetries.

Abstract

Using the (dynamical) density-matrix renormalization group method, we study the low-energy physics of three-leg antiferromagnetic Heisenberg model where the periodic boundary conditions are applied in the rung direction. We confirm that the spin excitations are always gapped as long as the intra-ring couplings form a regular triangle. From precise finite-size-scaling analyses of the spin gap and dimerization order parameter, we also find that the spin gap is collapsed by very small asymmetric modulation of the intra-ring couplings. Moreover, the dynamical spin structure factors on the intra- and inter-leg correlations are calculated. It is demonstrated that the low-lying structure of the inter-leg spectra is particularly affected by the asymmetric modulation.