Pseudogap, Fermi arc, and Peierls-insulating phase induced by 3D–2D crossover in monolayer VSe2

Abstract

One of important challenges in condensed-matter physics is to realize new quantum states of matter by manipulating the dimensionality of materials, as represented by the discovery of high-temperature superconductivity in atomic-layer pnictides and room-temperature quantum Hall effect in graphene. Transition-metal dichalcogenides (TMDs) provide a fertile platform for exploring novel quantum phenomena accompanied by the dimensionality change, since they exhibit a variety of electronic/magnetic states owing to quantum confinement. Here we report an anomalous metal-insulator transition induced by 3D-2D crossover in monolayer 1T-VSe2 grown on bilayer graphene. We observed a complete insulating state with a finite energy gap on the entire Fermi surface in monolayer 1T-VSe2 at low temperatures, in sharp contrast to metallic nature of bulk. More surprisingly, monolayer 1T-VSe2 exhibits a pseudogap with Fermi arc at temperatures above the charge-density-wave temperature, showing a close resemblance to high-temperature cuprates. This similarity suggests a common underlying physics between two apparently different systems, pointing to the importance of charge/spin fluctuations to create the novel electronic states, such as pseudogap and Fermi arc, in these materials.

Evidence of charge density wave with anisotropic gap in a monolayer VTe2 film

“…We note that the value of coupling ratio varies in different TMDCs systems, e.g., 6.4 and 17.85 for TaSe 2 monolayer [28,29]. The extracted ratio for VTe 2 film is larger than 3.52 expected for weak-coupled systems, and smaller than the recently reported values of 10 and 38 on monolayer VSe 2 [12,13].…”

Interaction of VSe2 with Ambient Gases: Stability and Chemical Reactivity

“…Vanadium diselenide (VSe 2 ), in the family of transition‐metal dichalcogenides, is triggering the interest of the scientific community due to several recent discoveries, including in‐plane piezoelectricity, a pseudogap with Fermi arc at temperatures above the charge‐density‐wave (CDW) transition temperature (≈220 K in the monolayer), and, especially, the emergence of room‐temperature ferromagnetism …”

Absence of Ferromagnetism in VSe2 Caused by Its Charge Density Wave Phase

“…A pseudogap appears at the Fermi surface [35] and the system remains paramagnetic [29,[35][36][37]. Remarkably, T CDW increases at the monolayer limit [7] and a gap opens at the Fermi level [9] with a controversial magnetic behavior for exfoliated [7] and MBE-grown monolayers [24]. However, a consistent picture about the microscopic origin of magnetism in VSe 2.0 and the development of FM order in this non-magnetic material in 2D is still lacking.…”