Wednesday Colloquia

Topology and quantum geometry in 2D moiré materials

by Prof. Mandar Deshmukh (TIFR Mumbai)

Wednesday, May 4, 2022 from to (Asia/Kolkata)
at AG-66 and via ZOOM webinar ( Zoom link: https://zoom.us/j/97963259354?pwd=ZFZsa2xqWGJSZW5pUjZPNkNqeGlEZz09 )
Meeting ID: 979 6325 9354 Pass code: 04072020
Description
Over the last 15 years there have been exciting developments in condensed matter physics and topological properties have been experimentally probed.  A revolution was possible because of engineering of novel effective Hamiltonians.  The electronic bands in such materials possess Berry curvature and topological invariants like Chern numbers due to quantum properties of the wavefunctions.  While Berry curvature [1] and its effects in materials have been studied, detecting changes in the topological invariant, Chern number, is challenging. We show in our experiments, using moiré bilayer graphene, that the first moment of Berry curvature detects topological transitions in the electronic bands. In our experiment, the perpendicular electric field tunes the valley Chern number and the Berry curvature dipole simultaneously permitting us to probe the physics of topological transitions [2]. 

References:

[1] Sinha* and Adak* et al. Nature Communications, 11, 5548 (2020). 
[2] Sinha* and Adak* et al. arXiv:2204.02848, accepted at Nature Physics .