Understanding if low-energy excitations can remain itinerant in the presence of strong disorder remains a central challenge in frustrated quantum magnets, where disorder is generally expected to localize excitations through Anderson-like mechanisms. Here we report the emergence of charge-neutral itinerant excitations in a van der Waals compound Cr3Se2Br5, a strongly disordered S=3/2 Mott insulator with a frustrated triangular lattice. Structural analysis reveals substantial intrinsic disorder arising from Cr-site deficiency and Se/Br-site mixing, which appear to be fixed and cannot be readily tuned. No long-range magnetic order or conventional glassy behavior is observed. In addition to its highly insulating nature, the magnetic specific heat C_mag/T and thermal conductivity \k{appa}_xx/T both exhibit linear temperature dependencies with substantial finite intercepts. In particular, a sizeable field-independent residual term κ/T≈0.03Wm−1K−2 is observed, providing compelling evidence of itinerant low-energy excitations that carry entropy without charge. These findings conceptually advance our understanding of quantum matter by demonstrating a rare regime where the interplay of disorder, frustration, and electronic correlations actively reshapes the nature of low-energy excitations, allowing itinerant neutral excitations to coexist with strong intrinsic disorder.
@article{arxiv.2605.25269,
title = {Non-local low energy neutral excitations in a strongly disordered triangular Mott magnet Cr$_3$Se$_2$Br$_5$},
author = {Wenhao Liu and Dechen Zhang and Yuanqi Lyu and Lebing Chen and Lifang Hu and Keith M. Teddei and Yuting Zhang and Steve Shelton and Moon Kim and Xiqu Wang and Michael A. Susner and James G. Analytis and Dung-Hai Lee and Lu Li and Bing Lv and Robert J. Birgeneau},
journal= {arXiv preprint arXiv:2605.25269},
year = {2026}
}