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Exploring Electronic Interactions and Topology in Flatlands 2D Crystals


Speaker:Dr. Dong-Keun Ki
Affiliation:Department of Quantum Matter Physics and Group of Applied Physics,
University of Geneva
Date:November 6, 2017 (Monday)
Time:4:30 p.m.
Venue:Room 522, 5/F, Chong Yuet Ming Physics Building, HKU

Abstract
 

Discovery of graphene has expanded our view of looking at electronic materials. It has shown that a variety of atomically thin 2D crystals can not only be obtained with an excellent quality, but also their electronic properties are different from those of their mother bulk materials, depending sensitively on the atomic structures as well as on the electro-chemical environments. It has therefore inspired many researches on 2D materials and numerous progresses have been made at an impressive pace. In particular, charge transport experiments have continuously revealed a multitude of new phenomena.

In this talk, I will first introduce the field from my own perspectives, explain what makes these 2D crystals so special and how they can be exploited to unveil the new transport phenomena. I will then discuss some of my recent contributions to the field—more specifically—in exploring the effects of interactions and a non-trivial topology. I will begin by showing that ultra-clean suspended graphene multilayers are strongly correlated 2D systems whose ground state properties are determined by Coulomb interactions. As a result, we have found several interesting phenomena, including i) a topologically non-trivial even-denominator fractional quantum-Hall effect in bilayer [1] and ii) finite-temperature phase transitions to a broken symmetry state in graphene multilayers [2-4]. All of these results are new and clearly illustrate that graphene multilayers form a unique family of closely related 2D systems that can exhibit interesting interactions effects with topologically non-trivial characters. At last, I will show that van der Waals (vdW) engineering can be used to enhance a spin-orbit coupling in graphene [5, 6], offering new ways to realize graphene-based topological states which can be accessed in detail by various experimental means. I will conclude this talk by discussing some of the important future implications of these results for the researches on Flatlands 2D crystals.

[1] Dong-Keun Ki, Vladimir I. Fal'ko, Dmitry A. Abanin, and Alberto F. Morpurgo, Nano Lett. 14, 2135 (2014)
[2] Anya L. Grushina, Dong-Keun Ki, Mikito Koshino, Aurelien A. L. Nicolet, Clément Faugeras, Edward McCann, Marek Potemski, and Alberto F. Morpurgo, Nat. Commun. 6, 6419 (2015)
[3] Youngwoo Nam, Dong-Keun Ki, Mikito Koshino, Edward McCann, and Alberto F. Morpurgo, 2D Mater. 3, 045014 (2016)
[4] Youngwoo Nam, Dong-Keun Ki, David Soler-Delgado, and Alberto F. Morpurgo, in preparation
[5] Zhe Wang, Dong-Keun Ki, Hua Chen, Allan H. MacDonald, and Alberto F. Morpurgo, Nat. Commun. 6, 8339 (2015)
[6] Zhe Wang, Dong-Keun Ki, Jun Yong Khoo, Diego Mauro, Helmuth Berger, Leonid S. Levitov, and Alberto F. Morpurgo, Phys. Rev. X 6, 041020 (2016)

Coffee and tea will be served 20 minutes prior to the seminar.

Anyone interested is welcome to attend.