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Monday, August 11 • 11:30 - 12:30
Topological Insulators I

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Invited: Yoichi Ando
Topological Qubit in Quantum Hall Systems: Materials Considerations

In this talk, I will present our recent results on fabrications and characterizations of topological insulator devices. We make devices using both thin films and exfoliated single crystals, and in either case the topological-insulator part is sufficiently bulk-insulating to allow access to the Dirac point by gating. One of our targets is to detect the spin response of the topological surface state using devices consisting of a topological insulator and a ferromagnet. Our spin pumping experiments, performed in collaboration with Prof. Eiji Saitoh's group at Tohoku University, gave clear evidence for spin-electricity conversion which takes place as a result of the spin-momentum locking when a fixed spin polarization is pumped into the topological surface state. We have also been trying to fabricate devices to address the peculiar surface state of topological crystalline insulators, where the physics is richer than in ordinary topological insulators and various novel applications can be conceived. An example of this class of materials is SnTe, and so far we have successfully grown SnTe thin films to address the peculiar (111) surface state and observed quantum oscillations coming from the Dirac cones of two different geometries.

Invited: Connie Li
Direct Electrical Detection of Spin-Momentum Locking in the Topological Insulator Bi2Se3

Topological insulator (TI) is a new quantum state of matter characterized by an insulating bulk with metallic surface states populated by massless Dirac fermions. One of its most striking properties is that of spin-momentum locking -- the spin of the TI surface state lies in-plane, and is locked at right angle to the carrier momentum. An unpolarized charge current should thus create a net spin polarization whose amplitude and orientation are controlled by the charge current. This remarkable property has been anticipated by theory, but never accessed in a simple transport structure. Here we show that a bias current indeed produces a net surface state spin polarization via spin-momentum locking in molecular beam epitaxially grown Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic metal contact. This voltage is proportional to the projection of the TI spin polarization onto the contact magnetization, is determined by the direction and magnitude of the bias current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than a Rashba effect. Similar data are obtained for structures with two different ferromagnet/tunnel barrier contacts, demonstrating that these behaviors are independent of the details of the detector contact. These results demonstrate direct electrical access to the TI surface state spin system and enable utilization of its remarkable properties for future technological applications. 

Co-authors: Olaf van 't Erve, Jeremy Robinson, Ying Liu, Lian Li, Berry Jonker

Session Chairs

Ramesh Mani

Georgia State University


Yoichi Ando

Professor, Institute of Scientific & Industrial Research, Osaka University
The research of Ando Laboratory focuses on growths of high-quality singe crystals and top-notch transport measurements of novel materials, such as topological insulators and topological superconductors. Our emphasis is on precise and systematic measurements of basic physical properties, which allows one to unveil the peculiar electronic states of novel materials. This is achieved by combining the expertise in solid-state physics and applied... Read More →

Connie Li

Research Scientist, Naval Research Laboratory
Connie H. Li is a staff research scientist in the Magnetoelectronic Materials & Devices section in the Materials Science & Technology Divison at the Naval Research Laboratory (NRL), Washington, DC. She received her B.S. and Ph.D. in 1998 and 2002 from the University of California, Los Angeles (UCLA), working on compound semiconductor surface reactions at an atomic scale in metal organic vapor phase epitaxy (MOVPE), during which she was... Read More →

Monday August 11, 2014 11:30 - 12:30
Room 18AB

Attendees (24)