Optical spin transfer torque observed

Experimental observation of the optical spin transfer torque.
P. Nemec1, E. Rozkotová, N. Tesarová, F. Trojánek, E. De Ranieri, K. Olejník, J. Zemen, V. Novák, M. Cukr, P. Malý and T. Jungwirth
Nature Physics AOL (2012)

Schematic illustration of the optical spin transfer torque. a, Schematic illustration of the optical spin transfer torque in the large spin lifetime limit. The rate P of the photo-carrier spin injection along the light propagation axis ˆn (normal to the sample plane) is completely transferred to the optical spin transfer torque (OSTT) acting along the normal to the sample plane on the magnetization M of the ferromagnet. The steady-state component of the injected spin density s0 is oriented in the plane of the sample and perpendicular to the in-plane equilibrium magnetization vector. The fast precessing component of the spin of a photo-carrier (small upper arrows) relaxes to the environment at a random orientation, producing a zero net momentum transfer to the environment. This picture applies to photo-electrons in (Ga, Mn)As. b, A weak torque acting on M (red arrow) produced by photo-carriers with a short spin lifetime. Most of the spin angular moment is transferred to the environment in this limit. For photo-holes in (Ga, Mn)As this picture is more relevant than the picture of the strong optical spin transfer torque shown in a.