Room Temperature Commensurate Charge Density Wave on Epitaxially Grown Bilayer 2H-Tantalum Sulfide on Hexagonal Boron Nitride

Abstract

The breaking of multiple symmetries by periodic lattice distortion at a commensurate charge density wave (CDW) state is expected to give rise to intriguing interesting properties. However, accessing the commensurate CDW state on bulk TaS2 crystals typically requires cryogenic temperatures (77 K), which precludes practical applications. Here, we found that heteroepitaxial growth of a 2H-tantalum disulfide bilayer on a hexagonal-boron nitride (h-BN) substrate produces a robust commensurate CDW order at room temperature, characterized by a Moiré superlattice of 3 × 3 TaS2 on a 4 × 4 h-BN unit cell. The CDW order is confirmed by scanning transmission electron microscopy and Raman measurements. Theoretical calculations reveal that the stabilizing energy for the CDW phase of the monolayer and bilayer 2H-TaS2-on-h-BN substrates arises primarily from interfacial electrostatic interactions and, to a lesser extent, interfacial strain. Our work shows that engineering interfacial electrostatic interactions in an ultrathin van der Waals heterostructure constitutes an effective way to enhance CDW order in two-dimensional materials.

Charge density waves and degenerate modes in exfoliated monolayer 2H-TaS2

“…Additionally, we can gain some insight into the commensurability of CDWs from temperature-dependent Raman spectroscopy. It is generally recognized that the commensurability of CDWs can change with temperature (Fu et al, 2020), but in the present work we find that the intensity of the CDWrelated Raman peak ($155 cm À1 ) is stable with changing temperature, implying that the CDWs observed in this experiment are probably completely commensurable. We therefore stress that the present work is the first to indicate that CDWs can exist in monolayer 2H-TaS 2 .…”

Experimental observations and density functional simulations on the structural transition behavior of a two-dimensional transition-metal dichalcogenide

“…To further confirm that the additional peaks observed at low temperature originate from the formation of a CDW, we calculated the phonon dispersion for the lattice dynamics of bulk and monolayer 2H-TaS 2 with and without the CDW phase based on density functional theory [24][25][26] and the PHONOPY code [13][14][15] . Details of the simulation can be found in "Methods" section.…”

Visualizing the Anomalous Charge Density Wave States in Graphene/NbSe2 Heterostructures

“…[ 1,2 ] Apart from the well‐studied 2D semiconducting MX 2 (e.g., M = Mo, W; X = S, Se), atomically thin metallic TMDs have a variety of prevailing collective many‐body phenomena, including the competing charge density wave (CDW) orders and superconductivity. [ 3–5 ] Understanding the electronic modulations of CDW states and the associated spontaneous periodic lattice distortions is significantly required to unveil the mechanism of coexisting phase diagram in low dimensions. [ 6,7 ]…”