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Multipole moments and fractional corner charges of insulating materials

Date : Friday, November 27th, 2020 16:00 - 17:00 Place : On Zoom (Please make a registration through the link below) Lecturer : Prof. Haruki Watanabe Affiliation : The University of Tokyo Committee Chair : Masaki Oshikawa (63275)
e-mail: oshikawa@issp.u-tokyo.ac.jp

How do we characterize and classify the insulating states of matter? Recent advances in the topological approach in condensed-matter physics offer a classification based on the winding and the quantum entanglement in the ground-state wavefunction. Although a nontrivial bulk topology is usually manifested as anomalous surface states, gapless modes are localized to the hinges and corners of the sample in the case of “higher-order” topology.

In this talk, we discuss that even absolutely topologically trivial materials may exhibit fractional charges on their corners and hinges. To predict these boundary signatures from the bulk, we develop a general formulation of bulk multipole moments, directly generalizing the “modern theory” formulation of the bulk polarization. As an example, we discuss e/8 fractional corner charges of grains of “table salt” and propose their direct measurement using atomic force microscopy.

HW and S. Ono, Phys. Rev. B 102, 165120 (2020)
HW and H. C. Po, arXiv:2009.04845.

(Published on: Monday November 16th, 2020)