Variational Monte Carlo study of spin dynamics in underdoped cuprates

TL;DR

This study uses variational Monte Carlo simulations of the $t$-$J$ model to investigate the origin of the hour-glass spin excitation spectrum in underdoped cuprates, emphasizing the role of stripe states.

Contribution

It provides a parameter-free numerical analysis of spin dynamics that clarifies the nature of the hour-glass dispersion, highlighting the collective mode and stripe state contributions.

Findings

Lower branch is a collective spin mode.

Upper branch likely results from stripe order.

Method satisfies no double-occupancy constraint.

Abstract

The hour-glass-like dispersion of spin excitations is a common feature of underdoped cuprates. It was qualitatively explained by the random phase approximation based on various ordered states with some phenomenological parameters; however, its origin remains elusive. Here, we present a numerical study of spin dynamics in the $t$-$J$ model using the variational Monte Carlo method. This parameter-free method satisfies the no double-occupancy constraint of the model and thus provides a better evaluation on the spin dynamics with respect to various mean-field trial states. We conclude that the lower branch of the hour-glass dispersion is a collective mode and the upper branch is more likely the consequence of the stripe state than the other candidates.