Large room-temperature valley polarization by valley-selective switching of exciton ground state

Excitonic Effects on Two-Dimensional Transition-Metal Dichalcogenide Monolayers: Impact on Solar Cell Efficiency

“…SOC plays a crucial role in the description of the electronic and optical properties of TMD monolayers. ,, Further, the lack of lattice inversion symmetry along with the strong SOC in 2H-TMDs results in a coupling of spin and valley pseudo-spin degrees of freedom. Thus, SOC effects were also included in the valence states for both PBE and HSE06 functionals via the second variational approach .…”

“…Due to the high computational cost to simulate optical properties with excitonic effect using DFT formalism as implemented in VASP, , we resort to BSE through the TB formalism, an accurate and expedite method to calculate excitonic properties. , The orthogonal TB Hamiltonian, H ( k ), obtained with maximum localized Wannier functions (MLWF) through the Wannier90 code, is given by where H 0 corresponds to the unitary cell Hamiltonian, which contains the on-site energies and hopping parameters inside the cell. The H R i terms represent the hopping matrices, which describe the interaction between neighbor cells.…”

“…TMD 2H monolayers based on Mo and W have been widely investigated in the literature. , They show two inequivalent valleys K and K ′ degenerated in the first Brillouin zone (BZ), in addition to a non-null Berry curvature . The monolayer inversion symmetry breaking, characteristic of the 2H structure, allows the access of valleys degrees of freedom selectively through optical helicity, enabling the probe and the manipulation of charge carriers in both valleys .…”

“…We perform a careful study of electronic, optical, and excitonic properties of the thermodynamic stable monolayers. We combine three methods to obtain a detailed knowledge of the PCE of TMD solar cells, namely, density functional theory (DFT), tight binding (TB), , and the Bethe–Salpeter equation (BSE). , Using our approach for BSE, we have access to the dark excitons (momentum and spin forbidden optical transitions), which do not appear in the absorption spectrum but have relevant effects on the optical properties through nonradiative channels. , In general, these states are not described by the usual DFT-GW + BSE approach. Further, using the proposed framework, we have access to the degree of freedom to change the dielectric environment around the monolayers.…”

A Single Chiral Nanoparticle Induced Valley Polarization Enhancement

“…[ 10,11 ] It is crucial to increase the contrast of valley‐dependent photoluminescence (PL) to build practical valleytronics devices for quantum information processing. [ 12–17 ] Yet, obtaining a clear valley contrast at room temperature (RT) is challenging, due to its severe contrast reduction by phonon‐assisted scattering processes. Consequently, the majority of the valley polarization experiments are limited to cryogenic temperature.…”