ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase

TL;DR

This study investigates magnetic excitations in a strong-leg quantum spin ladder compound using high-field ESR spectroscopy, revealing a gapped mode with unique non-linear behavior linked to longitudinal excitations and Dzyaloshinskii-Moriya interactions.

Contribution

The paper identifies and characterizes a novel ESR mode in a strong-leg spin ladder, combining experimental ESR data with theoretical calculations to reveal its origin.

Findings

Discovery of a gapped ESR mode with non-linear frequency-field dependence.

Identification of the mode as longitudinal excitations in the antisymmetric channel.

Linking the ESR mode to Dzyaloshinskii-Moriya interactions in the material.

Abstract

Magnetic excitations in the strong-leg quantum spin ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_4$ (known as DIMPY) in the field-induced Tomonaga-Luttinger spin liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual non-linear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe its ESR observability to the uniform Dzyaloshinskii-Moriya interaction.