Speaker: Chih-Kang Shih - Department of Physics, The University of Texas at Austin
Time: January 16, 2020 :: 2:00PM - 3:00PM
Recently, van der Waals heterostructures have emerged as a very powerful platform for designer quantum materials with many fascinating properties that are not possessed by the constituent monolayers achieving novel device functionality. In terms of designer vdW hetero-bilayers, the interlayer interaction is the controlling parameter determining the electronic structures of the heterostructure as a whole.
In this talk I will first discuss directly probing the inter-layer interactions in transition metal dichalcogenide (TMD) heterojunctions through the “lens” of moiré patterns using scanning tunneling microscopy and spectroscopy (STM/S). I will show that the interlayer coupling is strongly dependent on the interlayer atomic alignment of the constituent layers. Moreover, as a consequence of moiré pattern formation, the energy band structure of the hetero-bilayer also shows lateral modulation, forming a 2D electronic superlattice. The moiré pattern “lens” also provides us with a means to measure the 2D strain tensor with high precision and high spatial resolution. In addition, I will show how such strain profile modifies the electronic structures, including converting a type II to a type I band alignment.
As the periodic potential modulation also provides lateral confinement for excitons, an intriguing scenario occurs – the 2D lateral superlattices also form 2D exciton quantum dot arrays which can exhibit interesting optical properties. Recent reports on the observation of “moiré excitons” reveal only the tip of the iceberg of this exciting new frontier. Here I will present another example of how different degrees of freedom including stacking configuration, band alignment, and valley spin, work in concert to compose novel excitonic properties of TMD heterobilayers.