Non-magnetic Spintronics: How to add spin to a quantum billiard ball
- When?
- Thursday 1 March 2012, 1pm to 2pm
- Where?
- 02ATI02
- Open to:
- Students, Staff
- Speaker:
- Dr Steve Clowes
The realization of efficient semiconductor based spin filters and manipulators is essential for semiconductor spintronics to achieve its promised potential as a route to faster and more energy efficient electronics. One of the challenges is the creation of spin polarized currents within inherently non-magnetic semiconductors. The conventional approach to achieve this has been via the incorporation of magnetic materials. However, it may be possible to produce non-magnetic spin filters with very high efficiency by exploiting the strong spin-orbit interaction present in a number of semiconductors[1-3].
An important feature of these devices is that the transport regime is predominantly ballistic. In this respect, p-GaAs quantum wells (QWs) have been the material of choice [Rohkinson] due to their very large hole mobilities and the strength of spin-orbit coupling in the valence band. Recent advances in the growth of n-InSb QWs have resulted in mobilities in this material that now exceed 100,000 cm2V-1s-1 and have resulted in mean free paths of around 2 microns. In addition to this InSb has the strongest Rashba coefficient of all the III-Vs [4] making it an ideal candidate for ballistic spintronic devices.
We have investigated spin dependent transport in InSb QW nanoscale structures using spin polarised photocurrents[3]. We have demonstrated transverse magnetic focussing of photocurrent signals in an InSb/InAlSb quantum well device. Using optical spin orientation by modulated circularly polarized light an electron spin-dependent signal has been observed due to the spin-orbit interaction. In addition to this, simulations of the focusing signal have been performed using a classical billiard ball model, which includes both spin precession and a spin-dependent electron energy. The simulated data suggests that a signal dependent on the helicity of the incident light is expected for a Rashba parameter α > 0.1 eVÅ and that a splitting of the focusing signal is not expected to be observed in linear polarized photocurrent and purely electrical measurements. Whilst this results confirms the work of Rohkinson et al. it also demonstrates spin dependent focussing effect without the need of quantum point contacts or large in-plane magnetic fields to lift the spin degeneracy of these contacts.
I will also report on measurements of spin dependent transport in InSb nanowires using the same optical orientation technique described above. By applying weak magnetic fields ~200 mT we have observed a spin filtering effect which is caused by an asymmetry in the back scattering of electron from sidewall impacts due to a spin dependent cyclotron motion.
[1] L. P. Rokhinson, V. Larkina, Y. B. Lyanda-Geller, L. N. Pfeiffer, and K. W. West, “Spin Separation in Cyclotron Motion,” Phys. Rev. Lett. 93, 146601 (2004).
[2] M. Khodas, A. Shekhter, and A. M. Finkel’stein, “Spin Polarization of Electrons by Nonmagnetic Heterostructures: The Basics of Spin Optics,” Phys. Rev. Lett. 92, 086602 (2004).
[3] Juerong Li, A. M. Gilbertson, K. L. Litvinenko, L. F. Cohen, S. K. Clowes, “Transverse Focussing of Spin Polarized Photocurrents,” Phys. Rev. B. 85, 045431 (2012)
[4] M. A. Leontiadou, K. L. Litvinenko, A. M. Gilbertson, C. R. Pidgeon, W. R. Branford, L. F. Cohen, M. Fearn, T. Ashley, M. T. Emeny, B. N. Murdin, and S. K. Clowes, “Experimental determination of the Rashba coefficient in InSb/InAlSb quantum wells at zero magnetic field and elevated temperatures,” J. Phys. Condens. Matter 23, 035801 (2011).
