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Yong P. Chen: Manipulating Dirac Cones - from twisted bilayer graphene to hybridized topological insulator

posted 30 Apr 2019, 06:18 by Peter Boggild
Purdue University; WPI-AIMR; and Aarhus University

In 2013, we reported synthesis of twisted bilayer graphene (tBLG) by chemical vapor deposition (CVD), and observation of new low energy Raman modes in the tBLG, resonantly enhanced when photon energy matches the energy of van Hove singularities formed with two overlapping and offset Dirac cones from the two twisted graphene layers [1]. Using gate-tunable Raman spectroscopy and transport measurements in CVD-synthetic as well as mechanically stacked/exfoliated tBLG, we have studied electron-phonon coupling and other interesting band structure physics with two offset Dirac cones whose separation in momentum or energy may be tuned by twisting and electric field [2]. More recently, we showed that tuning the thickness and in-plane magnetic field may drive a ultrathin film of topological insulator into perhaps a simpler and more tunable analog of graphene (or analog of a Weyl semimetal in 2D) possessing two non-degenerate Dirac cones with field tunable separation [3].

[1] Rui He*, Ting-Fung Chung*, Conor Delaney, Courtney Keiser, Luis A. Jauregui, Paul M. Shand, C. C. Chancey, Yanan Wang, Jiming Bao, and Yong P. Chen (*equal contribution), "Observation of Low Energy Raman Modes in Twisted Bilayer Graphene", Nano Letters 13, 3594 (2013)

[2] Ting-Fung Chung, Rui He, Tai-Lung Wu, Yong P. Chen, "Optical Phonons in Twisted Bilayer Graphene with Gate-Induced Asymmetric Doping", Nano Letters 15, 1203 (2015); Ting-Fung Chung, Yang Xu, Yong P. Chen, "Transport measurements in twisted bilayer graphene: Studies of electron-phonon coupling and Landau level crossing", Physical Review B 98, 035425 (2018)

[3] Yang Xu, Guodong Jiang, Ireneusz Miotkowski, Rudro R. Biswas, and Yong P. Chen, "Tuning insulator-semimetal transitions in 3D topological insulator thin films by inter-surface hybridization and in-plane magnetic fields", arXiv:1904.03722

Yong P. Chen leads the “Quantum Matter and Devices Laboratory” that makes, measures and manipulates diverse quantum matter ranging from 2D/topological/hybrid quantum materials to atomic quantum gases, with potential applications such as energy, sensing and quantum technologies. He received a BSc and MSc in mathematics from Xi’an Jiaotong University and MIT, a PhD in electrical engineering from Princeton University, and did a physics postdoc at Rice University. He is a Professor of Physics and Astronomy and Professor of Electrical & Computer Engineering at Purdue University and the Inaugural Director of Purdue Quantum Science and Engineering Institute (PQSEI), a principal investigator in WPI-AIMR International Materials Research Center in Tohoku, Japan, and recently selected as a 2019 Villum Investigator in Denmark hosted at Aarhus University. Chen is a recipient of young investigator awards from NSF, DOD and ACS, an IBM faculty award, and Horiba Award, and is an elected Fellow of American Physical Society (APS).