Current Research

Spin-Orbit Materials Science and Device Physics
I have broad interests in spin transport, generation, manipulation and beyond, with a determination to contribute to furthering our scientific understanding and technological abilities. I am at the moment very much fascinated by a diverse range of phenomena arising from the spin-orbit interaction, in particular, that projects the real space (sample) structures and symmetries into spin structures in the (electronic) momentum space. These form a pivotal role in our modern physics and materials science research, often in the nanoscale, that I feel there are much more to explore. Understanding of the spin-orbit natures in condensed matter and resultant rational selections of appropriate materials&structures can potentially push the boundary of what it calls the state-of-the-art in the nanotechnology. In the following are my current specific research projects (but certainly will evolve and expand). 

1. The spin-orbit interaction for controlling various spin states
The coupling of spin and motion mediated by the spin-orbit interaction can provide a bi-lateral access of these two quantities - spin & motion (or transport), of electrons. As a result, the spin-orbit interaction can empower us to control electron spins through electric excitations - it seems we have better controllabilities of charge than spin as history explains. Electrons in a crystal with broken inversion symmetry experience different energy levels determined by the directions of both motion and spin. Controlling the motional component (by applying a current through), we can therefore access to the electron spin population. This is  a current-induced spin polarisation and if one does this in ferromagnetic materials, you can also control the localised electron spins that is hardly susceptible to applying a current - that's why they are called "localised". We are in part of an active international research collaboration (with many world-leading researchers in the world), and attempt to understand the microscopic pictures of current-induced spin polarisation and mangetisation control, in as view of harnessing for technology. Some details of this would be found in the following papers.

"An anti-damping spin-orbit torque originating from the Berry curvature", Nature Nanotech. 9 211 (2014)

“Spin-orbit-driven ferromagnetic resonance”, Nature Nanotech. 6 413 (2011).

2. Novel spin-Hall/spin-current phenomena and materials 
The spin-Hall effect is another branch of the spin-orbit phenomena, and using it is an alternative route for spin generation (and detection) pursuits. There is soon to be an interesting paper coming up from our research team, on which we provide an unusual way of controlling the spin-Hall effect. We will build on this study as well as examine several different research hypotheses to more understand and exploit the spin-Hall effect. Again, this project and ourselves benefit from its strong nature of international collaborations. Meanwhile, hope you enjoy our previous accounts.

"Electric control of the spin-Hall effect by inter-valley transitions" Nature Mater. 13 932 (2014)

"Polaron Spin Current Transport in Organic Semiconductors" Nature Phys. 10 308 (2014)

“Electrically tunable spin injector free from the impedance mismatch problem”  Nature Mater. 10 655 (2011).

3. Non-linear magnetic dynamics for fundamental spin physics and spintronic applications
In collaboration with Prof Demokritov's group, Germany, we work on fundamental physics about how (spin) angular momentum behave within spin-waves and other outer environments such as electrons and the lattice. Nonlinear magnetic dynamics is our particular focus, which sometimes offers very peculiar physics that often looks counter-intuitive but does not violate some fundamental thermodynamics rules. Our finding of spin current amplification using three-magnon splitting is just an example - learn more from the following links for this direction. 

“Controlled enhancement of spin current emission by three-magnon splitting”, Nature Mater. 10 660 (2011).

"Uniaxial anisotropy of two-magnon scattering in an ultrathin epitaxial Fe layer on GaAs" Appl. Phys. Lett. 102 082415 (2013).

“Spin pumping by parametrically excited short-wavelength spin waves” Appl. Phys. Lett. 99 162502 (2011).

Related book chapter in Recent Advances in Magnetic Insulators - From Spintronics to Microwave Applications, 83 (2013). 

4. 5..... Friday afternoon projects
My research ethos - I love people to just follow their thoughts of "it's cool to do this and that". I will secure some of my lab spaces dedicated to this, for more less fun-loving side of research that (at least) delocalises ourselves from productivity-oriented research that we normally do, or have to. There are a few ongoing projects like this, awaiting to find themselves materialised into some forms. Let me know if you wanna join us.

Our collaborations.
Dr A. J. Ferguson/Prof. H. Sirringhaus(and Dr. Watanabe)/Dr C. H. W. Barnes (Cambridge), Prof. B. Gallagher/A. Rushforth (Nottingham) and Dr A. Hirohata (York).
Prof. S. O. Demokritov (Munster), Prof T. Jungwirth (Prague) and Prof. J. Sinova (Mainz).
--The world--
Prof. E. Saitoh (Tohoku), Dr Ando (Keio) and Prof S. Mitani/Dr H. Sukegawa (NIMS).