Electron spin resonance modes in a strong-leg ladder in the Tomonaga-Luttinger liquid phase

M. Ozerov, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
M. Maksymenko, Max Planck Institute for the Physics of Complex Systems
J. Wosnitza, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
A. Honecker, Georg-August-Universität Göttingen
C. P. Landee, Clark University
M. M. Turnbull, Clark University
S. C. Furuya, Université de Genève
T. Giamarchi, Université de Genève
S. A. Zvyagin, HZDR - Helmholtz-Zentrum Dresden-Rossendorf

Abstract

Magnetic excitations in the strong-leg quantum spin ladder compound (C7H10N)2CuBr4 (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 nonlinear 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 their ESR observability to the uniform Dzyaloshinskii-Moriya interaction.