# Tailoring excitonic states of van der Waals bilayers through stacking configuration, band alignment and valley-spin

## TL;DR

This paper demonstrates a novel class of excitons in TMD bilayers that combine large optical and electric dipoles, achieved through layer-hybridization controlled by stacking, band alignment, and valley-spin configurations.

## Contribution

It introduces a new type of excitons in TMD bilayers that merge the benefits of monolayer and interlayer excitons via controlled layer-hybridization.

## Key findings

- Identification of layer-hybridized valley excitons in TMD bilayers
- Control of exciton properties through stacking and band alignment
- Potential applications in excitonic gases and quantum optics

## Abstract

Excitons in monolayer semiconductors have large optical transition dipole for strong coupling with light field. Interlayer excitons in heterobilayers, with layer separation of electron and hole components, feature large electric dipole that enables strong coupling with electric field and exciton-exciton interaction, at the cost that the optical dipole is substantially quenched (by several orders of magnitude). In this letter, we demonstrate the ability to create a new class of excitons in transition metal dichalcogenide (TMD) hetero- and homo-bilayers that combines the advantages of monolayer- and interlayer-excitons, i.e. featuring both large optical dipole and large electric dipole. These excitons consist of an electron that is well confined in an individual layer, and a hole that is well extended in both layers, realized here through the carrier-species specific layer-hybridization controlled through the interplay of rotational, translational, band offset, and valley-spin degrees of freedom. We observe different species of such layer-hybridized valley excitons in different heterobilayer and homobilayer systems, which can be utilized for realizing strongly interacting excitonic/polaritonic gases, as well as optical quantum coherent controls of bidirectional interlayer carrier transfer either with upper conversion or down conversion in energy.

---
Source: https://tomesphere.com/paper/1903.02157