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Optical Properties of Bi2Se3 Topological Insulators, Exotic Acousto-Piezoelectric Effects, and Contact Electrification Mechanisms
时间:2019-07-09 11:32    点击:   所属单位:先进材料与纳米科技学院
讲座名称 Optical Properties of Bi2Se3 Topological Insulators, Exotic Acousto-Piezoelectric Effects, and Contact Electrification Mechanisms
讲座时间 2019-07-11 14:30:00
讲座地点 西电南校区G-119
讲座人 Morten Willatzen
讲座人介绍
Prof. Morten Willatzen is a Talent 1000 Foreign Expert and Senior Full Professor at the Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences. He received his MSc degree from Aarhus University and the PhD degree from the Niels Bohr Institute at the University of Copenhagen. He also holds a Guest Professor position at the Department of Photonics Engineering, Technical University of Denmark and an Honorary Professorship at the Mads Clausen Institute, University of Southern Denmark. Morten Willatzen's research interests include solid state physics, mathematical physics, piezoelectricity, metamaterials and flow acoustics. He is the author of two books ‘’The k.p Method’’ published by Springer in 2009 and ‘’Separable Boundary-Value Problems in Physics’’ co-authored with Lok C. Lew Yan Voon.
 
Books:
1. L. C. Lew Yan Voon and M. Willatzen, "The k.p Method - Electronic Properties of Semiconductors," Springer, Berlin (ISBN 978-3-540-92871-3), 445 pages, August 2009.
2. M. Willatzen and L.C. Lew Yan Voon, "Separable Boundary-Value Problems in Physics,"
Wiley, Weinheim (ISBN 978-3-527-41020-0), 398 pages, April 2011.
讲座内容
A discussion of topological insulator applications and strain optimization of optical properties as well as two novel and exciting phenomena in acoustic structures are presented. In the first part of the presentation, three-dimensional topological insulators (TI) like Bi2Se3, Bi2Te3 and Sb2Te3 are important materials [1] for spintronics and provide a solid-state system displaying, on a low-energy scale, much of the high-energy physics of fermions including the presence of a Dirac cone in the dispersion. We present a group-theoretical discussion of the electronic bandstructure of the Bi2Se3 class of topological insulators and discuss energy harvesting properties [2]. The second part presents the coupling of piezoelectric equations and semiconductor drift-diffusion equations and demonstrates, in the plasma frequency range where the permittivity approaches zero, that large acoustic gains can be achieved under the action of a constant electric field by virtue of the Cherenkov effect. The gain can be several orders of magnitude. Device structures for acoustic amplification are also demonstrated theoretically. The third part of the presentation explores realization of parity-time symmetry phononic devices by designing a non-hermitean system Hamiltonian and the use of cleverly devised combinations of loss and gain. The gain blocks are piezoelectric materials activated in the Cherenkov regime [3]. In the final part of my presentation, I will discuss contact electrification and the influence of quantum mechanical effects.
 
References 

1.H. Zhang, C. Liu, X. Qi, X. Dai, Z. Fang, and S. Zhang, Nat. Phys. 5, 438 (2009).
2.M. R. Brems, J. Paaske, A. M. Lunde, and M. Willatzen, Phys. Rev. B 97, 081402(R) (2018).
3.J, Christensen, M. Willatzen, V. R. Velasco, and M.-H. Lu, Phys. Rev. Lett. 116, 207601 (2016).

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