Mott insulator tuning via structural distortion in monolayer 1T-NbSe2

TL;DR

This study demonstrates that the Mott insulating state in monolayer 1T-NbSe2 can be tuned through structural distortions and temperature, providing a pathway to manipulate quantum spin liquid regimes in two-dimensional materials.

Contribution

It reveals that structural distortions in monolayer 1T-NbSe2 can modulate the Mott gap, offering a new strategy to control Mott states and explore quantum spin liquids.

Findings

Monolayer 1T-NbSe2 exhibits two types of SD motifs with different Mott gaps.

Temperature variation can interconvert these SD motifs.

Bilayer 1T-NbSe2 shows Mott collapse due to interlayer coupling.

Abstract

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 analogy to TaS2 exempt from interlayer coupling, using spectroscopic imaging scanning tunneling microscopy and first principles calculations. Monolayer NbSe2 surprisingly displays two types of Star-of-David (SD) motifs with different Mott gap sizes, that are interconvertible via temperature variation. And, bilayer 1T-NbSe2 shows Mott collapse by interlayer coupling. Our calculation unveils the two types of SDs possess distinct structural distortions, altering the effective Coulomb energies of the central Nb orbital. Our calculation suggests the Mott gap, the same parameter for determining the QSL regime, is tunable with strain. This finding offers a general strategy for manipulating the Mott state in 1T-NbSe2 and related systems via structural distortions, which may be tuned into the potential QSL regime.