Trung tâm Vật lý lý thuyết - Trung tam Vat ly ly thuyet

Seminar Vật lý lý thuyết và Vật lý tính toán:
Tên báo cáo	Graphene pn junction in the quantum regime
Người trình bày	TS. Lê Trường Sơn
Cơ quan	Research Associate, National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, MD, USA
Ngày	Thứ Ba, 13-09-2016
Giờ	10:00 AM
Địa điểm	Phòng 202 (Thư viện), Viện Vật lý, 10 Đào Tấn, Ba Đình, Hà Nội
Tóm tắt	A pn junction is the interface between two semiconductor materials with opposite doping. PN junction devices are the foundation of model electronic industry today. Surprisingly, despite being intensively studied for more than 50 years, a pn junction interface still hosts a variety of very interesting physics. In this presentation, I will discuss the interesting quantum phenomena in a graphene pn junction device. Graphene, a two dimensional (2D) electronic system with its unique band structure, is a promising material for electrical metrology. Currently, GaAs heterostructures 2D electron gas (GaAs-2DEG) devices are used to realize the single quantum resistance standard value of h/2e2 = 12,906.4035 Ω with metrological accuracy. It is technologically relevant to realize quantum resistance values over a wider resistance scale. Graphene, with its unique ability to create both electron and hole 2D gases on a single Hall bar device without metal interconnects, is an idea platform for scalable resistance standards. We will present the fabrication and characterization of GpnJ in the quantum Hall regime showing multiple quantum resistance values other than h/2e2. Interesting physics of this system will be discussed. We found that the Landau level edge states from the p- and the n-section of a graphene P/N junction (pnJ) interact with each other differently across the junction depending upon the properties of the junction and the graphene. Full equilibration was reported for a two terminal graphene pnJ device in Williams et al. [1]. In our four-terminal device, however, only the lowest Landau level edge state is equilibrated across the pnJ [2,3]. Electrostatic simulations for our device geometry and that of [1] contrast the rate of change of the electrostatic potential across the pnJs, thus attributing to the difference in equilibration in the two devices. This open up the opportunities to fine tune the edge state interaction at the pnJ for desired quantum resistance values. Other quantum behavior of the graphene pnJ will be discussed. [1] J. R. Williams, L. DiCarlo, and C. M. Marcus, Science 317, 638 (2007) [2] Son T. Le, Nikolai N. Klimov, et al., Physical Review B – Rapid Communication 92, 241301 (12/2015) [3] Joseph A. Hagmann, Son T. Le et al., J. Vis. Exp. (107), e53506, 10.3791/53506 (2016)
Người chủ trì	Trịnh Xuân Hoàng

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