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"Spintronics based on Topological Insulators"

PI: John Q. Xiao, Co-PIs: Matt Doty, Stephanie Law, Branislav K. Nikolić
Department of Physics and Astronomy, University of Delaware, Newark DE 19716
Spin-orbit coupling (SOC) driven phenomena, such as current-induced magnetization switching,
auto-oscillation, and domain motion in magnetic heterostructures involving heavy metals or
topological insulators have attracted great attention. These phenomena arise from an intricate
combination of effects including the spin Hall effect (SHE), Rashba-Edelstein effect, and
Dzyaloshinskii-Moriya Interaction (DMI), which are strongly correlated with SOC in materials
and at interfaces. We propose a comprehensive research program that includes theoretical and
experimental efforts to unravel the rich SOC-driven phenomena in these ferromagnetic
heterostructures. Specifically, we will extend our novel magneto-optic Kerr effect spin torque
magnetometer to the time domain for charactering SO torque induced spin dynamics. Equipped
with these unique capabilities, along with heterostructures with designed interfaces to distinguish
between the SHE- and Rashba-driven SO torques, back-gated topological insulators to remove
the bulk effect of TIs, and a theoretical understanding of realistic structures, we anticipate
gaining a full understanding of SOC-driven phenomena in TL/FM heterostructures. The project
objectives are to: (1) measure three-dimensional SO torques on magnetization of arbitrary
direction in heterostructures of engineered interfaces in order to quantitatively separate the SHE
and Rashba contributions and understand their effects on magnetization dynamics; (2) develop
TI/FM heterostructures with perpendicular anisotropy and voltage controlled magnetic
anisotropy, and (3) perform first-principles theoretical and computational studies of SO torques
in order to understand the fundamental physical mechanisms behind them, which will guide us in
searching for and designing new material systems that possess optimal SO torque properties for
applications in ultralow-power memory and logic devices. The mission of the research program
is to advance fundamental knowledge in the basic sciences, a goal that directly fits the mission of
the DOE Basic Energy Sciences in general and the Materials Sciences and Engineering program
in particular. The proposal addresses the two grand challenges for condensed-matter and
materials physics for the next decade: (1) how to meet the energy demands of future generations;
and (2) how to extend the information technology revolution. Our team features strong
collaboration between experimentalists with expertise in materials fabrication, electrical,
magnetic, and optical measurements and a theorist with expertise in first-principles quantum
transport theory of realistic nanostructures and devices. The proposal balances risk and pay-off
by including projects based on demonstrated phenomena, as well as projects based on more
futuristic but justified thinking.