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Electro-Optic Excitations in van der Waals Materials for Active Nanophotonics


Biswas, Souvik (2023) Electro-Optic Excitations in van der Waals Materials for Active Nanophotonics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/tz4z-ed06.


van der Waals materials are emerging due to their unique properties such as atomic thickness, diverse quasiparticle optical resonances, and no requirement for lattice matching. While there is a vast variety of materials, semiconductors hold a special place for opto-electronic and linear/non-linear optical studies. Black phosphorus (BP), a 2D quantum-well with direct bandgap and puckered crystal structure, is a compelling platform for this research direction. In this thesis, we investigate fundamental optical excitations in novel low-dimensional quantum materials to achieve strong light-matter interaction and integrate with nanophotonic motifs for low-footprint, reconfigurable optical technology, focusing primarily on black phosphorus and transition metal dichalcogenides.

The thesis begins with the 'thin film limit' of van der Waals materials, between 5 and 20 nm thickness range. Chapters 2 and 3 explore how few-layer black phosphorus hosts interband and intraband optical excitations that can be strongly modified with gate-controlled doping and electric field, displaying epsilon near zero and hyperbolic behavior in the mid and far-infrared. In atomic thickness, strongly bound excitonic quasiparticles dominate the optical response. In Chapter 4, we investigate electrically tunable excitons in tri-layer black phosphorus, demonstrating a reconfigurable birefringent material that, when coupled with a Fabry-Perot cavity, enables the realization of a versatile and broadband polarization modulator. In Chapter 5, we examine the ultimate limit of a monolayer, studying MoTe2 via photoluminescence measurements and first-principles GW+BSE calculations, highlighting the Rydberg series associated with the exciton and its gate-tunability to understand strong electron-exciton interactions. In Chapter 6, we show how such excitons in monolayer black phosphorus can be strongly quantum confined at natural edges of exfoliated flakes, leading to highly temporally coherent emission. This emission is gate-tunable and understood via transmission electron microscopy and first-principles GW+BSE calculations of phosphorene nanoribbons to be originating from atomic reconstructions of the edge coupled with strain and screening effects.

Overall, our work highlights the potential of van der Waals materials for various electro-optical excitations and their applications in active nanophotonics.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:van der Waals materials; optics; nanophotonics; electro-optics; nanotechnology; 2D materials; black phosphorus; transition metal dichalcogenide
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Awards:Materials Research Society Graduate Student Award - Gold (2022)
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Atwater, Harry Albert
Group:Kavli Nanoscience Institute
Thesis Committee:
  • Nadj-Perge, Stevan (chair)
  • Hsieh, David
  • Faraon, Andrei
  • da Jornada, Felipe H.
  • Atwater, Harry Albert
Defense Date:30 March 2023
Non-Caltech Author Email:souvikdipon (AT)
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-07ER46405
Record Number:CaltechTHESIS:04032023-062047194
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 2 adapted for Chapter 3 adapted for Chapter 4 adapted for Chapter 5 adapted for Chapter 6
Biswas, Souvik0000-0002-8021-7271
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15127
Deposited By: Souvik Biswas
Deposited On:14 Apr 2023 18:03
Last Modified:08 Nov 2023 00:12

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