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Condensed Matter / Biophysics Seminar – Xiaomeng Liu (Princeton University)

Date January 9 @ 4:00 pm - 5:00 pm

VdW heterostructures: a new route to designing quantum matters

In quantum materials, fascinating phenomena arise from trillions of interacting electrons, such as superconductivity and non-abelian anyons. Harnessing these quantum properties is the key to future quantum technologies. Over the past decade, the development of two-dimensional (2D) materials and their heterostructures has revolutionized the quantum material field. Mechanically assembled layer-by-layer and held together by the van der Waals (vdW) force, vdW heterostructures place no constraint on constituent layers’ chemical compositions and lattice parameters. The versatility and tunability of these 2D platforms have enabled a wide range of quantum states of matter, spanning various correlated and topological orders.

In this talk, I will feature two examples of designing quantum matters with vdW heterostructures. The first example exploits Coulomb interactions across separate atomic layers to create a novel superfluid–the exciton condensate. By varying the pairing strength, the nature of this condensate is tuned from the strongly-coupled BEC regime to the weakly-coupled BCS regime, realizing the long-sought BEC-BCS crossover of fermion condensates. In the second example, two 2D layers (Bernal bilayer graphene) are placed directly on each other but with a twist. The beating between the two atomic lattices gives rise to a moiré pattern that defines a new length scale and reforms the energy structure. With electric control, highly-degenerate electron bands are achieved, leading to strong electron correlation and spontaneous symmetry breaking. More broadly, the rich interplays across atomic interfaces in vdW heterostructures provide gateways to major themes in condensed matter physics and new quantum devices, both of which will be the focus of my future lab. I will also briefly share my recent works and envisioned efforts to apply local probe techniques to reveal hidden quantum properties in 2D platforms.





January 9
4:00 pm - 5:00 pm
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2165 NPB