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Magnon hydrodynamics in an atomically thin ferromagnet
Ruolan Xue1, Nikola Maksimovic2, Pavel E Dolgirev2
1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
Science (New York, N.Y.)
|May 21, 2026
Summary
Researchers observed a novel two-dimensional magnon sound mode in chromium trichloride (CrCl3) using nitrogen-vacancy centers. This discovery advances understanding of strongly interacting magnons and their collective behaviors.
Area of Science:
- Condensed Matter Physics
- Quantum Magnetism
- Materials Science
Background:
- Strongly interacting particles can exhibit emergent collective excitations.
- Magnons (spin waves) are predicted to enter a hydrodynamic regime with a collective density mode.
- Chromium trichloride (CrCl3) is a material with strong magnon interactions.
Purpose of the Study:
- To investigate the collective dynamics of magnons in chromium trichloride.
- To experimentally verify the existence of a two-dimensional magnon sound mode.
- To explore the relationship between magnon interactions and temperature-dependent magnetic fluctuations.
Main Methods:
- Isolation of exfoliated chromium trichloride (CrCl3) sheets.
- Utilizing nitrogen-vacancy (NV) centers in diamond to measure magnon dynamics.
- Applying a variable-frequency drive field to multilayer CrCl3 samples.
- Spectroscopic analysis of magnetic fluctuations.
Main Results:
- Observed an anomalous increase in thermal magnetic fluctuations with decreasing temperature in monolayer CrCl3.
- Provided spectroscopic evidence for a two-dimensional magnon sound mode in multilayer CrCl3.
- Correlated the sharpening of a low-energy magnon sound mode with increasing magnon interactions.
Conclusions:
- The study demonstrates the existence of a collective magnon density mode in a 2D material.
- Findings suggest that strong magnon interactions lead to hydrodynamic behavior.
- The developed NV-center technique offers a new pathway for probing quantum magnetic phenomena.
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