Tuesday 28 July 2015 – Goetz Seibold - Intrinsic spin Hall effect in systems with striped spin-orbit coupling

After introducing the spin Hall effect, Götz described the basics in terms of the skew scattering mechanism and the side jump, and how in the stationary state, in a homogeneous system, the intrinsic conduction is cancelled by a diffusive contribution countering it.

Against this background he proposed to look at spatially non-homogeneous systems, and proposed a periodic modulation of the Rashba spin-orbit coupling for the 2-dimensional electron liquid (2DEL) at the interface between a thin lanthanum aluminate film and a strontium titanate substrate (LAO/STO). The modulation proposed could be achieved, e.g., putting periodically spaced metallic stripes as top electrodes to dope in a one-dimensionally

varying manner. The spin-orbit  coupling would be thus modulated, and the carrier concentration would also oscillate with maximal density for maximal coupling. The theory  is, however, much more general, quite applicable to very different systems, while keeping the periodic stripe geometry on a 2D system.

In this scenario, it seems that even the ground-state would display non-zero spin currents. Considering now the system in the presence of an applied electric field, but in the stationary situation, one finds suitable conditions for which one can get a non-zero spin-hall sigma, while keeping a zero “stationarity parameter” gamma  (i.e. the one which identifies the spin-hall conductivity of the equivalent homogeneous case).

Such a behaviour would be related to localised states at the stripes in the 2DEL. This Rashba spin-orbit coupling characteristics should be robust against disorder.

The charge transport would be strongly suppressed in the direction of the applied field, giving rise to large spin-hall angles.

The presentation was on the technical side, but offering good insights into the physics of the problem. As normal with last lectures in a dense session that is running late, the discussion was brief.  There was a question on the range of density where this effect is robust. The answer was that it corresponds (in the homogeneous- Rashba-coupling case) to the regime where a single chiral band is occupied. However, for the inhomogenenous case such an identification is not so simple. A second question was on the possibility to achieve the same effect with different inhomogeneous profiles for the Rahba coupling, and the answer was that in a previous work it was shown that if the Rashba coupling oscillates randomly aorund a fixed value it cannot be seen.

Blogged by Emilio Artacho