We report that MoX3 (X = I, Br) are rare van der Waals materials that exhibit signatures of both quantum spin chains with a spin singlet ground state and classical Neel order. Bulk single crystals grown by chemical vapor transport exhibit classical antiferromagnetic ground states with a transition temperature of ~40 K as revealed by susceptibility and specific heat measurements. Above 40 K, the susceptibilities show the large, broad peaks associated with a quantum spin-singlet ground state and large singlet-triplet gaps of 21 meV and 25 meV. Monte Carlo simulations, density matrix renormalization-group calculations for finite spin-3/2 chains, and density functional theory reproduce the experimental behavior, confirming the interplay between strong one-dimensional intrachain and weak three-dimensional interchain couplings. MoX3 offers a unique platform for exploring quantum magnetism and magnetic excitations at the atomic chain limit, as these materials combine a 1D van der Waals motif, spin chain behavior, and classical interchain order.
@article{arxiv.2510.12613,
title = {Quantum Spin Singlet and Classical N\'eel-Ordered Ground States in MoX3 (X = I, Br) Spin-3/2 Dimerized Antiferromagnetic Chain Crystals},
author = {Jordan Teeter and Topojit Debnath and Harshil Goyal and Md Sabbir Hossen Bijoy and Maedeh Taheri and Nicholas Sesing and Fariborz Kargar and Kirill Shtengel and Tina Salguero and Roger K. Lake and Alexander A. Balandin},
journal= {arXiv preprint arXiv:2510.12613},
year = {2025}
}