Critical fluctuations play a fundamental role in determining the spin orders for low-dimensional quantum materials, especially for recently discovered two-dimensional (2D) magnets. Here we employ the quantum decoherence imaging technique utilizing nitrogen-vacancy centers in diamond to explore the critical magnetic fluctuations and the associated temporal spin noise in van der Waals magnet Fe3GeTe2. We show that the critical fluctuation contributes to a random magnetic field characterized by the noise spectra, which can be changed dramatically near the critical temperature Tc. A theoretical model to describe this phenomenon is developed, showing that the spectral density is characterized by a 1/f noise near the Tc, while away from this point it behaves like a white noise. The crossover at a certain temperature between these two situations is determined by changing of the distance between the sample and the diamond. This work provides a new way to study critical fluctuation and to extract some of the critical exponents, which may greatly deepen our understanding of criticality in a wide range of physical systems.
@article{arxiv.2407.00647,
title = {Critical fluctuation and noise spectra in two-dimensional Fe$_{3}$GeTe$_{2}$ magnets},
author = {Yuxin Li and Zhe Ding and Chen Wang and Haoyu Sun and Zhousheng Chen and Pengfei Wang and Ya Wang and Ming Gong and Hualing Zeng and Fazhan Shi and Jiangfeng Du},
journal= {arXiv preprint arXiv:2407.00647},
year = {2024}
}