Emergence of a Metal–Insulator Transition and High-Temperature Charge-Density Waves in VSe₂ at the Monolayer Limit

Abstract

Emergent phenomena driven by electronic reconstructions in oxide heterostructures have been intensively discussed. However, the role of these phenomena in shaping the electronic properties in van der Waals heterointerfaces has hitherto not been established. By reducing the material thickness and forming a heterointerface, we find two types of charge-ordering transitions in monolayer VSe on graphene substrates. Angle-resolved photoemission spectroscopy (ARPES) uncovers that Fermi-surface nesting becomes perfect in ML VSe. Renormalization-group analysis confirms that imperfect nesting in three dimensions universally flows into perfect nesting in two dimensions. As a result, the charge-density wave-transition temperature is dramatically enhanced to a value of 350 K compared to the 105 K in bulk VSe. More interestingly, ARPES and scanning tunneling microscopy measurements confirm an unexpected metal-insulator transition at 135 K that is driven by lattice distortions. The heterointerface plays an important role in driving this novel metal-insulator transition in the family of monolayer transition-metal dichalcogenides.

Polymorphic Spin, Charge, and Lattice Waves in Vanadium Ditelluride

“…Vanadium ditelluride (VTe 2 ), a group 5 TMD, provides a platform for investigating the unexplored correlation between CDW and other quantum states, particularly those with magnetism 15–19. The moderate CDW transition temperature of bulk VTe 2 ( T C ≈ 480 K) compared with other CDW materials, such as VSe 2 ,20 allows a thorough study of the magnetism in its CDW phase. Since the late 1950s, both CDW and magnetic orderings have been separately reported in VTe 2 of various thicknesses;15–19,21 in the former studies, however, the powder and thin film‐based VTe 2 materials showed conflicting features regarding their lattice structure at room temperature 19,20,22.…”

“…The moderate CDW transition temperature of bulk VTe 2 ( T C ≈ 480 K) compared with other CDW materials, such as VSe 2 ,20 allows a thorough study of the magnetism in its CDW phase. Since the late 1950s, both CDW and magnetic orderings have been separately reported in VTe 2 of various thicknesses;15–19,21 in the former studies, however, the powder and thin film‐based VTe 2 materials showed conflicting features regarding their lattice structure at room temperature 19,20,22. Recent studies of thin VTe 2 films show that the interlayer interaction plays a role for the structural changes 18,23,24.…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…Several scanning tunneling microscopy (STM) (Figure B) and angle‐resolved photoemission (ARPES) studies (Figure C) have consistently confirmed the CDW order in MBE‐grown monolayer VSe 2 . The main controversy is however centered around its intrinsic magnetic state.…”

“…The main controversy is however centered around its intrinsic magnetic state. Bonilla et al and Duvjir et al indicated that a ferromagnetic state persists up to room temperature in monolayer VSe 2 , but their reported magnetizations of 15 and μ B per V atom remain to be debatable and disagree with the calculated value of ~0.6 μ B . On the other hand, Feng et al showed using ARPES and X‐ray magnetic circular dichroism (XMCD) that there are no exchange‐split V electronic bands and ferromagnetically coupled V atoms down to 10 K in an applied magnetic field of 9 T .…”

“…26 Several scanning tunneling microscopy (STM) ( Figure 5B) and angle-resolved photoemission (ARPES) studies ( Figure 5C) have consistently confirmed the CDW order in MBE-grown monolayer VSe 2 . 98,99,101,102 The main controversy is however centered around its intrinsic magnetic state. Bonilla et al and Duvjir et al indicated that a ferromagnetic state persists up to room temperature in monolayer VSe 2 , 99,101 but their reported magnetizations of 15 and μ B per V atom remain to be debatable and disagree with the calculated value of~0.6 μ B .…”