Manipulating the potential landscape of 2D materials through external dielectric screening

Atomically thin, quasi two-dimensional (2D) materials like semimetallic graphene and semiconducting transition metal dichalcogenide (TMDC) monolayers have been shown to have extraordinary optoelectronic properties, along with the possibility to tailor physical phenomena by assembling individual layers into novel heterostructures. The interaction between charge carriers in these 2D materials is strongly influenced by the local environment. By tuning the external dielectric screening, the band gap and exciton energies in 2D TMDCs can be modified to create lateral heterojunctions without modifying the material itself [1]. Using a combination of optical and angle-resolved photoemission spectroscopies with microscopic spatial resolution, we show that the band structure rigidly shifts in response to the change in local dielectric screening [2]. Furthermore, this environmental sensitivity can lead to a new type of disorder that leads to spatially inhomogeneous band gap and exciton energies as a consequence of spatial variations in the external dielectric screening rather than any material imperfections [3].
[1] A. Raja et al. Coulomb engineering of the bandgap and excitons in two-dimensional materials. Nature Communications 8, 15251 (2017)
[2] L. Waldecker*, A. Raja*, M. Rösner* et al. Rigid Band Shifts in Two-Dimensional Semiconductors through External Dielectric Screening. Physical Review Letters, In Press (2019)
[3] A. Raja*, L. Waldecker* et al. Dielectric disorder in two-dimensional materials. Nature Nanotechnology 14 (9), 832 (2019)