Engineering topics

Zhu, Dapeng

Publications and source records attributed to Zhu, Dapeng.

2 records

DOE OSTI2019

Nonlinear Planar Hall Effect

An intriguing property of a three-dimensional (3D) topological insulator (TI) is the existence of surface states with spin-momentum locking, which offers a new frontier of exploration in spintronics. In this work, we report the observation of a new type of Hall effect in a 3D TI $\mathrm{Bi_2Se_3}$ film. The Hall resistance scales linearly with both the applied electric and magnetic fields and exhibits a $\pi/2$ angle offset with respect to its longitudinal counterpart, in contrast to the usual angle offset of $\pi/4$ between the linear planar Hall effect and the anisotropic magnetoresistance. This novel nonlinear planar Hall effect originates from the conversion of a nonlinear transverse spin current to a charge current due to the concerted actions of spin-momentum locking and time-reversal symmetry breaking, which also exists in a wide class of noncentrosymmetric materials with a large span of magnitude. Finally, it provides a new way to characterize and utilize the nonlinear spin-to-charge conversion in a variety of topological quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Ultrafast Spin-to-Charge Conversion at the Surface of Topological Insulator Thin Films

Strong spin–orbit coupling, resulting in the formation of spin–momentum–locked surface states, endows topological insulators with superior spin–to–charge conversion characteristics, though the dynamics that govern it have remained elusive. Here, an all–optical method is presented, which enables unprecedented tracking of the ultrafast dynamics of spin–to–charge conversion in a prototypical topological insulator Bi 2 Se 3 /ferromagnetic Co heterostructure, down to the sub–picosecond timescale. Compared to pure Bi 2 Se 3 or Co, a giant terahertz emission is observed in the heterostructure that originates from spin–to–charge conversion, in which the topological surface states play a crucial role. A 0.12 ps timescale is identified that sets a technological speed limit of spin–to–charge conversion processes in topological insulators. Additionally, it is shown that the spin–to–charge conversion efficiency is temperature independent in Bi 2 Se 3 as expected from the nature of the surface states, paving the way for designing next–generation high–speed optospintronic devices based on topological insulators at room temperature.

36 MATERIALS SCIENCE↗