Topical review: the nature of the ground state and possibility of a quantum spin liquid in 1T metal dichalcogenides

Abstract

The compounds 1T-TaX2 (X = S, Se) and 1T-NbSe2 have been considered as potential hosts of a quantum spin liquid phase. This is based on the widely held view that the Mott-Hubbard mechanism drives the insulating behaviour of its charge density wave ground state, resulting in localized spins, interacting antiferromagnetically, on a geometrically frustrated lattice. However this assumes layer-wise independent behaviour. A growing body of evidence shows not only that inter-layer interactions are very significant in 1T-TaS2, but also that they mediate some of its most interesting functional properties. Here we offer a perspective from the point of view of scanning tunnelling microscopy that helps to visualize the microscopic degrees of freedom of inter-layer interactions in bulk 1T-TaS2, and the associated impact on the local density-of-states, including the occurrence of multiple distinct insulating phases. We consider to what extent the bulk of 1T-TaS2, and its surface terminations can be considered as Mott insulating and whether, or where, quantum spin liquid behaviour might persist. To better understand the bulk behaviour we also draw insights from measurements on isolated monolayers of 1T-TaX2 and 1T-NbSe2, where the confounding complications of inter-layer interactions are absent. We highlight some outstanding questions raised by a comprehensive evaluation of the experimental results, and finally suggest future experiments that could address them.

45 pages, 24 figures. Accepted for publication in Journal of Physics: Condensed Matter

References in corpus (48)

• Identifying Topological Order by Entanglement Entropy
• Correlated Insulating States at Fractional Fillings of the WS2/WSe2 Moiré Lattice
• Spin liquid phase of the $S=\frac{1}{2}$ $J_1-J_2$ Heisenberg model on the triangular lattice
• Band insulator to Mott insulator transition in 1T-TaS${}_2$
• Imaging spinon density modulations in a 2D quantum spin liquid
• Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet
• Gapless excitations in the ground state of 1T-TaS${}_2$
• The low-temperature highly correlated quantum phase in the charge-density-wave 1T-TaS_2 compound
• Monolayer 1T-NbSe2 as a 2D correlated magnetic insulator
• Direct identification of Mott Hubbard band pattern beyond charge density wave superlattice in monolayer 1T-NbSe2
• Correlated electronic states at domain walls of a Mott-charge-density-wave insulator 1T-TaS2
• Distinguishing a Mott Insulator from a Trivial Insulator with Atomic Adsorbates
• Rearrangement of uncorrelated valence bonds evidenced by low-energy spin excitations in YbMgGaO4
• Ba8CoNb6O24: a spin-1/2 triangular-lattice Heisenberg antiferromagnet in the 2D limit
• Heat transport study of the spin liquid candidate 1T-TaS2
• Evidence for a spinon Kondo effect in cobalt atoms on single-layer 1T-TaSe${}_2$
• Effect of Stacking Order on the Electronic State of 1T-TaS${}_2$
• Possible strain induced Mott gap collapse in 1T-TaS${}_2$
• Mott versus hybridization gap in the low-temperature phase of $1T$-TaS${}_2$
• Evidence of Dirac Quantum Spin Liquid in YbZn2GaO5
• Mott insulator tuning via structural distortion in monolayer 1T-NbSe2
• Spectral function of the $J_1-J_2$ Heisenberg model on the triangular lattice
• Dynamical Signatures of Symmetry Broken and Liquid Phases in an $S=1/2$ Heisenberg Antiferromagnet on the Triangular Lattice
• Zoology of domain walls in quasi-2D correlated charge density wave of 1T-TaS2
• Multiple crossovers and coherent states in a Mott-Peierls insulator
• Presence and absence of itinerant gapless excitations in the quantum spin liquid candidate EtMe${}_3$Sb[Pd(dmit)${}_2$]${}_2$
• Magnetic Impurity as a Local Probe of the U(1) Quantum Spin Liquid with Spinon Fermi Surface
• Exploring the Charge Density Wave phase of 1$T$-TaSe${}_2$: Mott or Charge-transfer Gap?
• $\text{Ab initio}$ theory of magnetism in two-dimensional $1T$-TaS${}_2$
• Surface structure and stacking of the commensurate $\left(\sqrt{13}\times \sqrt{13}\right)$R13.9° charge density wave phase of 1T-TaS${}_2$(0001)
• Ba8MnNb6O24: a model two-dimensional spin-5/2 triangular lattice antiferromagnet
• Fractionalization on the Surface: Is Type-II Terminated $1T$-TaS${}_2$ Surface an Anomalously Realized Spin Liquid?
• Large optical tunability from charge density waves in 1T-TaS${}_2$ under incoherent illumination
• Quantum billiards with correlated electrons confined in triangular transition metal dichalcogenide monolayer nanostructures created by laser quench
• Low-energy behavior of spin-liquid electron spectral functions
• Charge density wave surface reconstruction in a van der Waals layered material
• Doublon-like excitations and their phononic coupling in a Mott charge-density-wave system
• Proposal to detect emergent gauge field and its Meissner effect in spin liquids using NV Centers
• Electronic Density of States of a $U\left(1\right)$ Quantum Spin Liquid with Spinon Fermi Surface. I. Orbital Magnetic Field Effects
• Twisted Bogoliubov quasiparticles in the superconducting NbSe${}_2$ monolayer on graphene
• Electronic Density of States of a $U\left(1\right)$ Quantum Spin Liquid with Spinon Fermi Surface. II. Zeeman Magnetic Field Effects
• Origin of Distinct Insulating Domains in the Layered Charge Density Wave Material 1T-TaS2
• Spectroscopic evidence for possible quantum spin liquid behavior in a two-dimensional Mott insulator
• Identification of soft modes across the commensurate-to-incommensurate charge density wave transition in 1$T$-TaSe${}_2$
• Controlling magnetic frustration in 1T-TaS${}_2$ via Coulomb engineered long-range interactions
• Interlayer Hopping between Surface Mott Insulator and Bulk Band Insulator in layered 1T-TaS_{2}
• Behavior under magnetic field of resonance at the edge of the upper Hubbard band in 1T-TaS2
• Probing complex stacking in a layered material via electron-nuclear quadrupolar coupling