报告人：Yong P. Chen ，普渡大学

报告时间：6月16日10：30

报告地点：理科楼三楼报告厅（理科楼C-302）

报告题目：Quantum Transport in Graphene and Topological Insulator Materials

报告摘要：Graphene and topological insulators (TI) are among the most actively studied quantum materials in current condensed matter physics. In this talk, I will present selected experiments performed in my group studying quantum electronic transport in such novel materials and related nanostructures.

Part 1. Graphene provides a flexible, transferrable 2D electron system (2DES) with new opportunities not available in traditional 2DES. We show that large scale synthetic graphene grown by chemical vapor deposition (CVD) is intrinsic graphene by observing the characteristic half-integer quantum Hall effect (QHE), even in graphene films as large as center-meters. Using polycrystalline and single crystalline graphene synthesized by CVD, we study the electronic properties such as scattering at individual grain boundaries and graphene edges by transport measurements, STM and Raman mapping. In unconventional structures such as single layer-bilayer graphene hybrid structures, we find a QHE that breaks particle-hole as well as time-reversal (magnetic field) symmetry.

Part 2. Bi2Se3 is one of the “prototype” TI materials. While most charge transport studies on such TI materials focus on samples with low bulk conduction/doping to enhance the signal from topological surface state, we have studied n-type Bi2Se3 with very high doping and discovered a 2D-like magnetotransport and bulk QHE. Our analysis and control experiments show that the observed QHE is a bulk effect, rather than a surface effect. We attributed it to the parallel quintuple layers (QL) making up the bulk. While there is not yet a theoretical explanation of our data, we suggest a new electronic state may form in the bulk at such high doping regime and discuss some possibilities. Finally I will present some spin-valve measurements with magnetic contacts yielding interesting results consistent with spin-momentum locking of surface state transport, and suggest that spin transport might be a more sensitive probe of surface state than charge transport.