Giant Valley Coherence at Room Temperature in 3R WS ₂ with Broken Inversion Symmetry

Abstract

<jats:p>Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties. In 3R-stacked transition metal dichalcogenides, the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum, providing an unprecedented platform for valleytronics. Here, we study the valley coherence of 3R WS<jats:sub>2</jats:sub> large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature. Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence. The valley coherence of direct A (B) excitons can reach 0.742 (0.653) with excitation conditions on resonance with it. Such giant and thickness-independent valley coherence of large single-crystal 3R WS<jats:sub>2</jats:sub> at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.</jats:p>

Anomalously polarised emission from a MoS2/WS2heterostructure

“…It has been reported earlier that in WS 2 , compared to ML, even though the emission is weaker in thicker flakes, thicker flakes give rise to a higher degree of polarization. [32][33] Hence we have chosen a 3L thick WS 2 to form the HS. The top panel of figure 1(b) shows the PL from the triangular heterostructure region, which is similar to what has been reported earlier.…”

Routing valley exciton emission of a WS2 monolayer via delocalized Bloch modes of in-plane inversion-symmetry-broken photonic crystal slabs

“…The emergence of two-dimensional transition metal dichalcogenides (TMDCs) has attracted tremendous interest for their possible applications in valleytronics [1][2][3][4][5][6][7][8][9][10][11][12] . Due to the broken inversion symmetry in TMDCs, two types of degenerate yet inequivalent valleys (labelled K and K' valleys) appear at the corners of the first Brillouin zone, as shown in Fig.…”

Polarization-Dependent Optical Properties and Optoelectronic Devices of 2D Materials

“…However, graphene is not an ideal material to study the valley polarization PL due to its limited ability in opening the band gap. Beyond graphene, the group of TMD is promising as semiconductors for valleytronics, due to their direct band gaps in the visible spectral range [ 148 , 149 ]. As one of the typical TMD materials, the MoS 2 monolayer has a hexagonal lattice structure with C3 symmetry.…”