Quantum Noise Spectroscopy of Criticality in an Atomically Thin Magnet

TL;DR

This paper demonstrates the use of nitrogen-vacancy center-based noise magnetometry to analyze critical magnetic fluctuations in a 2D magnet, revealing deviations from classical models and suggesting XY criticality.

Contribution

First application of T2 noise magnetometry to quantitatively study critical dynamics in a 2D magnetic material, revealing the influence of long-range interactions.

Findings

Extracted critical exponent ν deviates from Ising model predictions.

Indications of 2D-XY criticality near the Curie temperature.

Demonstrated the capability of T2 noise magnetometry for critical scaling analysis.

Abstract

Dynamic critical fluctuations in magnetic materials encode important information about magnetic ordering in the associated critical exponents. Using nitrogen-vacancy centers in diamond, we implement $T_2$ (spin-decoherence) noise magnetometry to study critical dynamics in a 2D Van der Waals magnet CrSBr. By analyzing NV decoherence on time scales approaching the characteristic correlation time $\tau_c$ of critical fluctuations, we extract the critical exponent $\nu$ for the correlation length. Our result deviates from the Ising prediction and highlights the role of long-range dipolar interactions in 2D CrSBr. Furthermore, analyzing the divergence of the correlation length suggests the possibility of 2D-XY criticality in CrSBr in a temperature window near $T_C$ where static magnetic domains are absent. Our work provides a first demonstration of $T_2$ noise magnetometry to quantitatively analyze critical scaling behavior in 2D materials.