Optical Spectroscopy of Moiré Structures: Light-Induced Effective Magnetic Field in Atomic Thin Materials Open Access

Wu, Jiatian (Spring 2020)

Permanent URL: https://etd.library.emory.edu/concern/etds/h128ng05f?locale=en


When atomic thin materials (ATMs) are brought together with a small twist angle, the heterobilayer system gives rise to some new optical and magnetic properties, such as moiré excitons and emergent many-body phases. Due to Coulomb interaction between the electrons and holes in a semiconductor, they are bound as pairs named excitons and determine the optical response such as light absorption and emission. Our lab focuses on the study of transition metal dichalcogenides (TMDs) such as MoSe2 and WSe2 , which are unique in a way that their charge carriers possess a ”valley” degree of freedom which acts like a pseudo spin and can be controlled by helicity of light. The valley-dependent optical selection rules allow us to manipulate the valley degree of freedom and investigate exciton interactions through light polarization techniques. Our group has previously shown a repulsive dipoledipole interaction between excitons, and now we report an additional exciton exchange interaction within the same valley species. Moreover, we find that the exchange interaction induces a magnetic-field-like effect, which can be manipulated by optical pumping. The finding of the optical-induced splitting provides another knob to control the valley degree of freedom and can be applied to future ”valleytronics” applications, in which information is stored and processed in the valley degree of charge carriers.

Table of Contents

1 Introduction

1.1 Atomic Thin Materials

1.2 Optical Properties of TMDs

1.3 Moir´e Superlattice

1.4 State of a Two-Spin System

1.5 Zeeman-like Splitting

2 Methods

2.1 Sample Fabrication

2.2 Photoluminescence Spectroscopy

3 Results and Discussion

3.1 Zero Magnetic Field Measurements

3.2 Magnetic Field measurements

4 Conclusion

5 Future Work

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