Quantum loops in the 1T transition metal dichalcogenides
arXiv:2409.03819 · doi:10.1103/PhysRevB.111.L020102
Abstract
Loop arrangements and their quantum superpositions describe several interesting many-particle states. We propose that they also describe bonding in a class of transition metal dichalcogenides. We present an effective quantum loop model for monolayers with 1T structure and a d valence electron configuration: materials of the form MX (M = Mo, W and X=S, Se, Te) and AMY (A = Li, Na; M = V, Nb and Y = O, S, Se). Their t orbitals exhibit strongly directional overlaps between neighbouring atoms, favouring the formation of valence bonds. A transition metal atom forms two valence bonds, each with one of its neighbours. When connected, these bonds form loops that cover the triangular lattice. We construct a minimal Rokhsar-Kivelson-like model with resonance processes that cut and reconnect loops that run in proximity. The resulting dynamics is more constrained than in traditional quantum dimer models, with a `bending' constraint that arises from orbital structure. In the resulting phase diagram, we find phases that resemble distorted phases seen in materials, viz., the 1T and trimerized phases. As a testable prediction, we propose that a single d or d impurity will terminate a loop and give rise to a long-ranged texture. For example, a Ti/Cr defect in LiVO will produce one or more domain walls that propagate outward from the impurity. We discuss the possibility of a loop liquid phase that can emerge in these materials.
6 pages, 4 figures, includes 3-page supplement
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