Correlated_phases_and_dynamics_of_excitons_in_van_der_Waals_heterostructures Public

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

Rights statement

• Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.

School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, Condensed Matter Physics, Optics Physics, Low Temperature
Mot-clé	Semiconductors 2D materials vdW materials Optics
Committee Chair / Thesis Advisor	Ajit Srivastava, Emory University
Committee Members	Lili Wang, Emory University Luiz Santos, Emory University

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