Spin dynamics in the presence of competing ferro- and antiferro-magnetic correlations in Yb2Ti2O7

TL;DR

This paper investigates the spin excitation spectra of Yb2Ti2O7, revealing a broad continuum likely linked to quantum spin liquid behavior, with classical models failing to fully explain the observations.

Contribution

It provides a detailed analysis of the spin dynamics in Yb2Ti2O7, highlighting the limitations of classical simulations and suggesting a quantum spin liquid state near phase competition.

Findings

Broad, temperature-insensitive excitation continuum up to 1.5 meV.

Classical simulations underestimate the energy scale and cannot fully reproduce the spectra.

Yb2Ti2O7 is near a phase boundary between ferro- and antiferromagnetic states.

Abstract

In this work, we show that the zero field excitation spectra in the quantum spin ice candidate pyrochlore compound \ybti\ is a continuum characterized by a very broad and almost flat dynamical response which extends up to $1-1.5$ meV, coexisting or not with a quasi-elastic response depending on the wave-vector. The spectra do not evolve between 50 mK and 2 K, indicating that the spin dynamics is only little affected by the temperature in both the short-range correlated and ordered regimes. Although classical spin dynamics simulations qualitatively capture some of the experimental observations, we show that they fail to reproduce this broad continuum. In particular, the simulations predict an energy scale twice smaller than the experimental observations. This analysis is based on a careful determination of the exchange couplings, able to reproduce both the zero field diffuse scattering and the spin wave spectrum rising in the field polarized state. According to this analysis, \ybti\ lies at the border between a ferro and an antiferromagnetic phase. These results suggest that the unconventional ground state of \ybti\ is governed by strong quantum fluctuations arising from the competition between those phases. The observed spectra may correspond to a continuum of deconfined spinons as expected in quantum spin liquids.