Spin Dynamics in Quantum Sine-Gordon Spin Chains: High-Field ESR Studies

Abstract

A spin-1/2 Heisenberg antiferromagnetic chain is one of the most important paradigmatic models in quantum magnetism. Its ground state is a spin singlet, while the excitation spectrum is formed by gapless fractional excitations, spinons. The presence of alternating g-tensors and/or the staggered Dzyaloshinskii-Moriya interaction results in opening the energy gap $$\varDelta \propto H^{2/3}$$ Δ ∝ H 2 / 3 , once the magnetic field H is applied. A fairly good understanding of this phenomenon was achieved in the framework of the sine-Gordon quantum-field theory, taking into account the effective transverse staggered field induced by the applied uniform field. The theory predicts solitons and antisolitons as elementary excitations, as well as their bound states, breathers. Here, I review recent high-field electron spin resonance spectroscopy studies of such systems, focusing on peculiarities of their spin dynamics in the sine-Gordon regime and beyond.

High Field Electrical Polarization and Magnetoelectric Coupling in Chiral Magnet [Cu(pym)(H2O)4]SiF6·H2O

“…Quantum spin chains are the fundamental building blocks of quantum magnetism. As we seek to understand magnets of increasing complexity, starting with a single spin and working our way up to many body systems, the linear spin chain is the first system we encounter that shows quantum many-body behavior in the form of gaps, collective excitations, fractionalized excitations, and order parameters. − Surprisingly, chiral spin chains are under-explored, despite the fact that chirality is implicated in a number of exciting and unexpected properties. − [Cu­(pym)­(H 2 O) 4 ]­SiF 6 ·H 2 O was recently recognized as a chiral spin chain with properties that differ significantly from those of a traditional linear spin chain. , This metal–organic material forms chiral chains of S = 1/2 Cu 2+ ions along the c -axis where the spiral has a periodicity of four Cu centers [Figure (a)]. The Cu spins are interspersed by meta-linked pyrimidines that provide the primary exchange interaction along the chains. ,, The exchange interaction is antiferromagnetic ( J = −42 K) based on susceptibility, heat capacity, and magnetization .…”