55th CEMS Colloquium


Prof. Junsaku Nitta (Tohoku University)


17:30 - 18:30, November 22, 2017 (Wednesday)


Okochi-Hall, RIKEN


Spin-orbitronics in Semiconductors


Spins of electrons had been so far manipulated by magnetic field since the magnetic moments of spins is directly coupled with a magnetic field. Spin-orbit interaction (SOI) originated from an electric field is a relativistic effect, i.e. electrons feel an effective magnetic field when they move in an electric field. The effective magnetic field induced by SOI can create spin-related functionalities. Now much attention is focused on spintronics utilizing SOI, the so-called spin-orbitronics [1], since generation, manipulation and detection of spins are made by all electrical means via SOI. Here, we will discuss spin-orbitronics in semiconductor nano-structures.

In III-V compound semiconductor heterostructures, there exist both Rashba and Dresselhaus SOIs originated from structural and bulk inversion asymmetries, respectively. Especially, the Rashba SOI is quite useful since the strength is controlled by a gate electric field. For electrical spin generation, a Stern-Gerlach-type spin filter is experimentally demonstrated using a quantum point contact with strong Rashba SOI [2]. The electrical manipulation of spin precession is possible in an Aharonov-Casher spin interferometer where the spin dynamic and geometric phases are controlled [3]. A mobile spin resonance without any magnetic field is experimentally demonstrated in a winding channel with SOI [4]. The Stern-Gerlach spin filter based on SOI can be used for electrical spin detection.

However, as drawback of SOI, the effective magnetic field caused by SOI is momentum dependent, leading to spin relaxation. One of effective ways to suppress the spin relaxation is to make the persistent spin helix symmetry where the strength of Rashba SOI is equal to that of Dresselhaus SOI. Based on a novel method directly to evaluate the ratio between the Rashba and Dresselhaus SOIs, a gate controlled persistent spin helix state is experimentally demonstrated [5]. Further enhanced distance of spin coherent propagation is realized by drift spin transport [6].

[1] A. Manchon, et al., Nature Mat. 14, 871 (2015).
[2] M. Kohda, et al., Nature Comm. 3, 2080 (2012).
[3] F. Nagasawa, et al., Nature Comm. 4, 3526 (2013).
[4] H. Sanada, et al., Nature Phys. 9, 280 (2013).
[5] A. Sasaki, et al., Nature Nanotech. 13, 703 (2014).
[6] Y. Kunihashi, et al., Nature Comm. 7, 10722 (2016).