JOINT ICTP/SISSA CONDENSED MATTER SEMINARS: "Spin Hall Drag"

[CM]

JOINT ICTP/SISSA CONDENSED MATTER SEMINARS



Seminar Room - ICTP Leonardo Building (first floor)

  					Wednesday, 9 September   -   4:00 p.m.



Samvel M. BADALYAN

( Yerevan State University, Armenia & University of Regensburg,  
Germany )

"Spin Hall Drag"





Abstract



Double-layer structures, consisting of two parallel quantum wells  
separated by a potential barrier,  are an important class of nanoscale  
electronic devices. Each layer hosts a quasi-two-dimensional electron   
gas and electrons interact across the barrier via Coulomb interaction.  
The combined action of the spin and  pseudo-spin (associated with the  
layer index) degrees of freedom creates new phases in these bilayers   
where the spin and many-body interaction effects play a critical role.

When an electric current is driven in one (active) layer of the bi- 
layer, the inter-layer Coulomb  interaction causes charge accumulation  
in the other (passive) layer. This phenomenon, known as Coulomb  drag,  
is of fundamental interest as a probe of electron correlations.  
Another effect of great interest is the  Spin Hall Effect, the  
generation of spin accumulation by an ordinary electric current. The  
spin Hall effect  is due to spin-orbit interaction and SOI and has  
been a subject of vigorous research both in  semiconductors and metals  
in recent years not only because of its theoretical subtlety but also  
as a  potential source of spin polarized currents.

Lately, we have predicted and analyzed theoretically a new effect in  
bi-layers, which combines the  interesting features of spin Hall  
effect and Coulomb drag. We call it Spin Hall Drag. SHD consists in  
the  generation of spin accumulation across the passive layer by an  
electric current flowing along the other  layer. Besides being a  
striking example of an effect that depends simultaneously on Coulomb  
interactions  and spin-orbit coupling, the SHD has several unexpected  
and non-trivial features. It occurs in the absence  of a current in  
the passive layer and, as we have shown, it is predominantly caused by  
a subtle effect  known as side-jump in electron-electron collisions.  
This is at variance with the ordinary spin Hall effect,  which, for  
electrons in GaAs, is dominated by an effect known as skew-scattering.  
We have shown that  the skew-scattering and the side-jump  
contributions (considered for the first time in a context of  
electron-  electron scattering) are separated by different temperature  
dependences at low temperature T, with the  former vanishing much  
faster than the latter (T 3 vs T 2). Our calculations indicate that  
the induced spin  accumulation is large enough to be detected in  
optical rotation experiments.