Excitations and quasi-one-dimensionality in field-induced nematic and spin density wave states

摘要

We study the excitation spectrum and dynamical response functions for severalquasi-one-dimensional spin systems in magnetic fields without dipolar spinorder transverse to the field. This includes both nematic phases, which harbor"hidden" breaking of spin-rotation symmetry about the field and have beenargued to occur in high fields in certain frustrated chain systems withcompeting ferromagnetic and antiferromagnetic interactions, and spin densitywave states, in which spin-rotation symmetry is truly unbroken. Usingbosonization, field theory, and exact results on the integrable sine-Gordonmodel, we establish the collective mode structure of these states, and show howthey can be distinguished experimentally.