Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets

TL;DR

This study investigates the spin dynamics in two quasi-one-dimensional antiferromagnets using nuclear magnetic resonance, revealing a universal quantum critical behavior as excitations transition from magnons to spinons.

Contribution

It demonstrates the universal quantum critical scaling of spin dynamics in different gapped 1D antiferromagnets through experimental NMR measurements.

Findings

Spin excitations evolve from magnons to spinons with magnetic field.

The relaxation rate 1/T1 exhibits quantum critical scaling.

Universal behavior observed across different systems.

Abstract

By means of nuclear spin-lattice relaxation rate 1/T1, we follow the spin dynamics as a function of the applied magnetic field in two gapped one-dimensional quantum antiferromagnets: the anisotropic spin-chain system NiCl2-4SC(NH2)2 and the spin-ladder system (C5H12N)2CuBr4. In both systems, spin excitations are confirmed to evolve from magnons in the gapped state to spinons in the gapples Tomonaga-Luttinger-liquid state. In between, 1/T1 exhibits a pronounced, continuous variation, which is shown to scale in accordance with quantum criticality. We extract the critical exponent for 1/T1, compare it to the theory, and show that this behavior is identical in both studied systems, thus demonstrating the universality of quantum critical behavior.