2D materials and van der Waals heterostructures

The physics of two-dimensional (2D) materials and heterostructures based on such crystals has been developing extremely fast. With new 2D materials, truly 2D physics has started to appear (e.g. absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc). Novel heterostructure devices are also starting to appear - tunneling transistors, resonant tunneling diodes, light emitting diodes, etc. Composed from individual 2D crystals, such devices utilize the properties of those crystals to create functionalities that are not accessible to us in other heterostructures. We review the properties of novel 2D crystals and how their properties are used in new heterostructure devices

Plasmon-exciton polaritons in 2D semiconductor/metal interfaces

The realization and control of polaritons is of paramount importance in the prospect of novel photonic devices. Here, we investigate the emergence of plasmon-exciton polaritons in hybrid structures consisting of a two-dimensional (2D) transition metal dichalcogenide (TMDC) deposited onto a metal substrate or coating a metallic thin-film. We determine the polaritonic spectrum and show that, in the former case, the addition of a top dielectric layer, and, in the latter, the thickness of the metal film,can be used to tune and promote plasmon-exciton interactions well within the strong coupling regime. Our results demonstrate that Rabi splittings exceeding 100 meV can be readily achieved in planar dielectric/TMDC/metal structures under ambient conditions. We thus believe that this work provides a simple and intuitive picture to tailor strong coupling in plexcitonics, with potential applications for engineering compact photonic devices with tunable optical properties.Comment: 6 pages, including 5 figures and reference

Magnetoexcitons in transition-metal dichalcogenides monolayers, bilayers, and van der Waals heterostructures

We study direct and indirect magnetoexcitons in Rydberg states in monolayers and heterostructures of transition-metal dichalcogenices (TMDCs) in an external magnetic field, applied perpendicular to the monolayer or heterostructures. We calculate binding energies of magnetoexcitons for the Rydberg states 1$s$, 2$s$, 3$s$, and 4$s$ by numerical integration of the Schr\"{o}dinger equation using the Rytova-Keldysh potential for direct magnetoexcitons and both the Rytova-Keldysh and Coulomb potentials for indirect magnetoexcitons. Latter allows understanding the role of screening in TMDCs heterostructures. We report the magnetic field energy contribution to the binding energies and diamagnetic coefficients (DMCs) for direct and indirect magnetoexcitons. The tunability of the energy contribution of direct and indirect magnetoexcitons by the magnetic field is demonstrated. It is shown that binding energies and DMCs of indirect magnetoexcitons can be manipulated by the number of hBN layers. Therefore, our study raises the possibility of controlling the binding energies of direct and indirect magnetostrictions in TMDC monolayers, bilayers and heterostructures using magnetic field and opens an additional degree of freedom to tailor the binding energies and DMCs for heterostructures by varying the number of hBN sheets between TMDC layers. The calculations of the binding energies and DMCs of indirect magnetoexcitons in TMDC heterostructures are novel and can be compared with the experimental results when they will be available.Comment: 21 pages, 9 figures, 6 tables. arXiv admin note: text overlap with arXiv:2011.0309

A generic tight-binding model for monolayer, bilayer and bulk MoS2

Molybdenum disulfide (MoS2) is a layered semiconductor which has become very important recently as an emerging electronic device material. Being an intrinsic semiconductor the two-dimensional MoS2 has major advantages as the channel material in field-effect transistors. In this work we determine the electronic structure of MoS2 with the highly accurate screened hybrid functional within the density functional theory (DFT) including the spin-orbit coupling. Using the DFT electronic structures as target, we have developed a single generic tight-binding (TB) model that accurately produces the electronic structures for three different forms of MoS2 - bulk, bilayer and monolayer. Our TB model is based on the Slater-Koster method with non-orthogonal sp3d5 orbitals, nearest-neighbor interactions and spin-orbit coupling. The TB model is useful for atomistic modeling of quantum transport in MoS2 based electronic devices.Comment: 4 pages, 2 figures, 3 table