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In bulk samples and few layer flakes, the transition metal dichalcogenides NbS$_2$ and NbSe$_2$ assume the H polytype structure with trigonal prismatic coordination of the Nb atom. Recently, however, single and few layers of 1T-NbSe$_2$…
Using ab-initio calculations we reveal the nature of the insulating phase recently found experimentally in monolayer 1T-NbSe$_2$. We find soft phonon modes in a large parts of the Brillouin zone indicating the strong-coupling nature of a…
The recently investigated $1T$-polymorph of monolayer NbSe$_2$ revealed an insulating behaviour suggesting a star-of-David phase with $\sqrt{13}\,\times\sqrt{13}$ periodicity associated with a Mott insulator, reminiscent of $1T$-TaS$_2$. In…
Mott state in 1T-TaS2 is predicted to host quantum spin liquids (QSL). However, its insulating mechanism is controversial due to complications from interlayer coupling. Here, we study the Mott state in monolayer 1T-NbSe2, an electronic…
The applicability of DFT+$U$ to the star-of-David phase of $1T$-TaS$_2$ is examined. The viability of a Mott phase as a ground state for the bulk of this material is briefly discussed in light of the available experimental evidence.
Inspired by recent discovery of correlated insulating states in twisted bilayer graphene (TBG), we study a two-orbital Hubbard model on the honeycomb lattice with two electrons per unit cell. Based on the real-space density matrix…
Understanding Mott insulators and charge density waves (CDW) is critical for both fundamental physics and future device applications. However, the relationship between these two phenomena remains unclear, particularly in systems close to…
1$T$-TaSe$_2$ is widely believed to host a Mott metal-insulator transition in the charge density wave (CDW) phase according to the spectroscopic observation of a band gap that extends across all momentum space. Previous investigations…
Electron-phonon-driven charge density waves can in some circumstances allow electronic correlations to become predominant, driving a system into a Mott insulating state. New insights into both the Mott state and preceding charge density…
The properties of 2D materials are strongly influenced by their substrate, leading to a variety of "proximity effects" like screening, charge transfer, and hybridization. Surprisingly, there is a dearth of theoretical studies on these…
We investigate the low-temperature charge-density-wave (CDW) state of bulk TaS$_2$ with a fully self-consistent DFT+U approach, over which the controversy has remained unresolved regarding the out-of-plane metallic band. By examining the…
Combination of low-dimensionality and electron correlation is vital for exotic quantum phenomena such as the Mott-insulating phase and high-temperature superconductivity. Transition-metal dichalcogenide (TMD) 1T-TaS2 has evoked great…
Using ab initio methods based on density functional theory, the electronic and magnetic structure of layered hexagonal NbSe$_{2}$ is studied. In the case of single-layer NbSe$_{2}$ it is found that, for all the functionals considered, the…
Monolayer 1T-TaS$_2$ hosts a star-of-David charge-density wave (CDW) that stabilizes a low-temperature Mott-insulating state. Recent time-resolved spectroscopies indicate a coupling between the CDW amplitude mode and the electronic…
Monolayer group-V transition metal dichalcogenides in their 1T phase have recently emerged as a platform to investigate rich phases of matter, such as spin liquid and ferromagnetism, resulting from strong electron correlations. Although 1T…
Electron-electron and electron-phonon interactions are two major driving forces that stabilize various charge-ordered phases of matter. The intricate interplay between the two give rises to a peculiar charge density wave (CDW) state, which…
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…
Motivated by the recent experimental evidence of commensurate surface charge density waves (CDW) in Pb/Ge(111) and Sn/Ge(111) sqrt{3}-adlayer structures, as well as by the insulating states found on K/Si(111):B and SiC(0001), we have…
In condensed matter physics, various mechanisms give rise to distinct insulating phases. The competition and interplay between these phases remain elusive, even for the seemingly most distinguishable band and Mott insulators. In multilayer…
Layered transition metal dichalcogenide 1T-NbSe_2 is a good candidate to explore the charge density wave (CDW) and Mott physics. However, the effects of stacking orders and interlayer coupling in CDW 1T-NbSe_2 are still less explored and…