A Universal Rule for Controlling Spin Currents in Quantum Spin Hall Systems
Update: 2018-02-24 09:34:00      Author: yangjuan@csrc.ac.cn

A long-standing interest in spintronics is generating and transporting spin current (SC) in condensed matter systems. The discovery of pure spin current (PSC), for example, spin Hall current, that is decoupled from charge current (CC) has opened up exciting opportunities for spin transport, because it is expected that the transport of PSC has much smaller energy dissipation compared with that of conventional SC generated by ferromagnetic materials. Quantum spin Hall (QSH) system can exhibit exotic spin transport properties, especially, a transverse edge PSC of QSH effect can be generated under a four-terminal device setting. However, spin conservation mandates that there is no net SC under a two-terminal device setting in a QSH system. Although discovering new mechanism to control the SC and/or transverse PSC in a QSH system is of great importance for spintronics, its development is still at its infancy.

Recently, Prof. Bing Huang’s group in CSRC in collaboration with Feng Liu’s group in the University of Utah proposed a new concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system, as shown in Figure 1. They show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics. 

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FIG. 1: (a)–(c) Schematic diagrams of spin current and charge current flowing along the edges as the bending angle increases from 0 (a) to 180 (c). A pair of edge states counter propagate along all four edges subject to TRS. The spins rotate adiabatically along the curved edges. The highlight of spin directions at the two opposite edges under the same charge current flow direction is shown in the bottom of (a)–(c). (d) Calculated spin conductance for the QSH ribbons with different bending angle in a two-terminal device setting. (e) The values of spin conductance in the QSH regime (plateau region) in (d) as a function of bending angle.

 

References:

[1]   B. Huang, K. Jin, B. Cui, F. Zhai, J. Mei, and F. Liu, Nature Comm. 8, 15850 (2017).


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