Correlated_phases_and_dynamics_of_excitons_in_van_der_Waals_heterostructures 公开
Hadjri, Zacharia (Spring 2024)
Abstract
Semiconducting transition metal dichalcogenides (TMDs) couple strongly to light via the excitation of electrons from the valence band to the conduction band, leaving a hole in the valence band. The excited electron binds to the hole forming an exciton, a hydrogenic quasiparticle. The interactions between excitons and between excitons and charge carriers can realize interesting phases of matter, especially in multi-layer stacks of TMDs. Heterostructures with type-II band structures can host interalyer excitons with a finite out-of-plane dipole moment. Furthermore, either a twist angle between layers or a large lattice mismatch can generate a moir\'{e} potential with a lattice constant orders of magnitude of larger than the underling lattices. This emergent long-wavelength potential is felt by both excitons and charge carriers.
In this thesis, we report firstly on the observation of electric-field tunable quadrupolar excitons in a WS$_2$/WSe$_2$/WS$_2$ heterotrilayer and an interaction-driven quadrupolar-to-dipolar transition. Secondly, we describe the decay dynamics of interacting Moire excitons in a WS$_2$/WSe$_2$ heterobilayer where the exciton lifetime at short times increases with power up to hundreds of nanoseconds.
Table of Contents
1 Introduction
2 Background
2.1 TMD vdW Superlattices
2.1.1 Dipolar interlayer excitons in heterobilayers
2.2 Moir´e superlattices
3 Methods
3.1 Exfoliation
3.2 Sample assembly
3.3 Optical measurements
3.3.1 Time-resolved PL measurements
4 Quadrupolar Excitons in a WSe2/WS2 Heterobilayer
4.1 Experimental Details
4.2 Evidence of Quadrupolar Excitons
4.2.1 Model
4.2.2 AB-stacked heterotrilayer
4.3 Control of excitonic lifetime with electric field
4.4 Interaction-driven quadrupolar-dipolar transition
4.5 Exchange splitting and signatures of anti-ferroelectric correlations
About this Honors Thesis
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