Quantum Projection in an Ising Spin Liquid

TL;DR

This study investigates how a transverse magnetic field influences the susceptibility of a quantum magnet, revealing complex multi-spin collective behavior beyond simple pair interactions.

Contribution

It demonstrates the role of quantum projection in an Ising spin liquid and highlights the limitations of pairwise models in explaining off-diagonal responses.

Findings

Clusters of strongly-coupled spins dominate the response

Pair calculations reproduce some features but not all

Evidence of multi-spin collective states

Abstract

A transverse magnetic field is used to scan the diagonal and off-diagonal susceptibility of the uniaxial quantum magnet, $\text{LiHo}_{0.045}\text{Y}_{0.955}\text{F}_4$. Clusters of strongly-coupled spins act as the primary source for the response functions, which result from a field-induced quantum projection of the system into a classically forbidden (meaning non-Ising) regime. Calculations based on spin pairs reproduce only some features of the data and fail to predict the measured off-diagonal response, providing evidence of a multi-spin collective state.