R. G. Herb Condensed Matter Seminars

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Events During the Week of February 19th through February 26th, 2023

Monday, February 20th, 2023

No events scheduled

Tuesday, February 21st, 2023

Interacting Opto-Moiré Quantum Matter
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Xi Wang, U Washington
Abstract: Moiré superlattices of 2D materials are an emerging platform for studying new physical
phenomena with high tunability. Strong excitonic responses in Transition Metal Dichalcogenides
(TMDs) allow optical access to the wealth of correlated physics. In this talk, I will present our
recent results about interactions between moiré excitons and charge carriers trapped in moiré
potentials. We have discovered a new interaction between exciton and charges enabled by
unusual quantum confinement in 2D moiré superlattices, which results in novel exciton many-
body ground states composed of moiré excitons and correlated electron lattices. The phase
diagram is further enriched when we investigate the magnetic interactions with optical
excitation. We have observed that the spin-spin interactions between moiré trapped holes can be
drastically tuned by optical excitation power, pointing to the excitons mediated long-range
exchange interaction between moiré trapped carriers. This discovery adds a new and dynamic
tuning knob to the rich many-body Hamiltonian of moiré quantum matter. Our work provides the
framework for understanding and engineering electronic and excitonic states in moiré quantum
Host: Victor Brar
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Wednesday, February 22nd, 2023

No events scheduled

Thursday, February 23rd, 2023

VdW heterostructures: a new route to designing quantum matters
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Xiameng Liu, Princeton
Abstract: From superconductivity to fractionalized particles, fascinating phenomena arise in quantum materials due to the collective behaviors of electrons. These quantum effects challenge our intuition about nature and provide new opportunities for future quantum information technologies. Recently, two-dimensional materials and their heterostructures have become a leading platform for realizing new quantum states of matter. Mechanically assembled layer-by-layer and held together by the van der Waals (vdW) force, vdW heterostructures break through the limitations of traditional material synthesis and offer entirely new ways to create quantum matters. My talk will feature two examples of designing quantum matters with vdW heterostructures. In the first example, I will illustrate how Coulomb interactions across separate atomic layers pair fermions (electrons and holes) into bosons to achieve a superfluid condensate state. Thanks to the tunability of the vdW platform, we can vary the pairing strength and change the nature of this fermion condensate from strong coupling to weak coupling, demonstrating a long-sought paradigm known as the BEC-BCS crossover. In the second example, I will introduce the idea of moiré band engineering, where the interference between two atomic lattices—named the moiré pattern—defines a new periodicity and reforms electronic band structures. In twisted double bilayer graphene, such moiré periodicity creates highly-degenerate bands tunable by a perpendicular electric field. We observed electron correlation effects, including interaction-driven insulation and spontaneous symmetry breaking of spins. Their evolution with the electric fields reveals their close connection with the moiré band features. Finally, I will briefly discuss applications of local probe techniques to uncover hidden quantum properties in vdW platforms and share visions of leveraging rich interplays across atomic interfaces to access major themes in condensed matter physics.
Host: Victor Brar
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Friday, February 24th, 2023

No events scheduled