# Temperature evolution of spin dynamics in two- and three-dimensional Kitaev models: Influence of fluctuating gauge fluxes

## TL;DR

This study investigates how spin dynamics evolve with temperature in 2D and 3D Kitaev models, revealing distinct behaviors related to gauge flux fluctuations and phase transitions, using an advanced unbiased numerical method.

## Contribution

Develops a novel QMC+CTQMC numerical approach to study low-temperature spin dynamics in Kitaev models, overcoming previous limitations and enabling analysis of gauge flux effects.

## Key findings

- Smooth crossover in 2D honeycomb case
- Singular behavior at phase transition in 3D hyperhoneycomb case
- Low-temperature spin dynamics sensitive to gauge flux fluctuations

## Abstract

The long-sought quantum spin liquid is a quantum-entangled magnetic state leading to the fractionalization of spin degrees of freedom. Quasiparticles emergent from the fractionalization affect not only the ground state properties but also thermodynamic behavior in a peculiar manner. We here investigate how the spin dynamics evolves from the high-temperature paramagnet to the quantum spin liquid ground state, for the Kitaev spin model describing the fractionalization into itinerant matter fermions and localized $Z_2$ gauge fluxes. Beyond the previous study [J. Yoshitake, J. Nasu, and Y. Motome, Phys. Rev. Lett. $\textbf{117}$, 157203 (2016)], in which the mean-field nature of the cluster dynamical mean-field theory prevented us from studying low-temperature properties, we develop a numerical technique by applying the continuous-time quantum Monte Carlo (CTQMC) method to statistical samples generated by the quantum Monte Carlo (QMC) method in a Majorana fermion representation. This QMC+CTQMC method is fully unbiased and enables us to investigate the low-temperature spin dynamics dominated by thermally excited gauge fluxes, including the unconventional phase transition caused by gauge flux loops in three dimensions, which was unreachable by the previous methods. We apply this technique to the Kitaev model in both two and three dimensions. Our results clearly distinguish two cases: while the dynamics changes smoothly through the crossover in the two-dimensional honeycomb case, it exhibits singular behaviors at the phase transition in the three-dimensional hyperhoneycomb case. We show that the low-temperature spin dynamics is a sensitive probe for thermally fluctuating gauge fluxes that behave very differently between two and three dimensions.