Observation of magnetodielectric coupling in a quantum spin liquid candidate

A quantum spin liquid state is predicted to emerge in materials where magnetic order is suppressed by geometric frustration. This state may be modeled by the two-dimensional spin-1/2 antiferromagnetic Heisenberg Kagome lattice, which is realized in the wide-gap insulator YCu₃(OH)₆Br₂[Br_1-x(OH)_x] (YCOB). Our recent studies of this material under high magnetic fields have demonstrated the existence of unconventional magnetization plateaus consistent with a spin-liquid state [1]. Surprisingly, we also observed unconventional quantum oscillations in the region of the 1/9th saturation magnetization plateau. These suggest that the low level excitations of this state are fractionalized fermions. In order to determine the exact nature of these excitations, we have turned to study the dielectric properties of this exciting material.

Here, we report the observation of magnetodielectric coupling in YCOB under high magnetic fields. We metalized single crystal samples to serve as parallel plate capacitors, and observed shifts in their capacitance under high DC and pulsed magnetic fields. These observations suggest a link between the magnetodielectric coupling and the low-level excitations of the system.

[1] Zheng, G., et al., Unconventional magnetic oscillations in a kagome Mott insulator. Proceedings of the National Academy of Sciences, 2025. 122(5).