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Colloquium: Dr. Biswajit Datta | The City College of NY

In-Person PHYS 401


Physics : 401

Date & Time

February 16, 2024, 11:00 am12:00 pm


TITLE:  “Topological Electronic Transport and Hybrid Light–Matter States in quantum materials”

ABSTRACT: Quantum materials allow the investigation and engineering of exotic quantum states that deepen our understanding and have the potential in technological applications. Among these materials, layered van der Waals substances form a unique class, exfoliatable down to atomically thin layers. The reduced thickness facilitates precise control of electronic and photonic states through external electric and magnetic fields. Our research approach involves making ultraclean heterostructures from various quantum materials, achieving remarkable mobility exceeding 500,000 cm²V⁻¹s⁻¹ (for graphene). We employ two complementary measurement techniques—quantum electronic transport and optical spectroscopy to investigate different macroscopic quantum phenomena. In the first part of the talk, we will focus on the electronic transport of trilayer graphene in the quantum Hall regime—a multiband Dirac material hosting both massless and massive electrons [1,2,3]. We will briefly discuss the quantum Hall effect of coexisting massless and massive electrons in this system. Utilizing quantum Hall resistance oscillations, we will explore how band topology influences the quantum phase (Berry's phase) of an electron's wavefunction, introducing a mechanism for measurement of Berry's phase when traditional methods fall short. Transitioning to the second part, we will discuss the physics of strong light-matter coupling in layered semiconductors, manifesting as emergent quasiparticles—exciton-polaritons in semiconductor microcavities. Specifically, we will discuss the realization of exciton-polaritons with a permanent electric dipole moment in bilayer transition metal dichalcogenides, leveraging dipole-dipole interactions for high optical nonlinearity [4]. Lastly, we will investigate exciton-polaritons in magnetic materials [5], demonstrating control over their flow in an anisotropic magnetic material, CrSBr. In the end, we will discuss how the synergistic application of cavity and device physics can allow us to study emergent phenomena like the polariton Hall effect and polariton photocurrent.

[1] Nature Communications 8, 14518 (2017)

[2] Physical Review Letters 121, 056801 (2018)

[3] Science Advances 5, 10 (2019)

[4] Nature Communications 13, 6341 (2022)

[5] Nature Nanotechnology 17, 1060 (2022)