Detecting Spin Currents in Ballistic Nanostructures
J. A. Folk1,2, R.M. Potok2, C. M. Marcus2
1
Department of Physics, Stanford University, 2Department of Physics, Harvard
University
Many recent experiments have probed the spin transport properties of mesoscopic
structures such as quantum point contacts and quantum dots. They have been motivated
both by a desire to understand the fundamental spin physics of these few-electron
systems where coherence and interactions both play critical roles, and by the possibility
of using them as spin manipulation devices for spintronics and quantum information
processing applications. One difficulty with most of these experiments is that they
attempt to decipher spin effects from, for example, the effects of an in-plane magnetic
field on transport measurements or even-odd correlations in an energy level structure,
sometimes making interpretation of the results unclear.
In this talk, we present a new technique to measure the spin-polarization of currents
from mesoscopic devices directly, using a small perpendicular magnetic field to bend
and focus the ballistic electron trajectories of current from the device under test into a
spin selective collector (a quantum point contact in a large in-plane field) in the standard
transverse electron focusing geometry. We have tested the technique using the
relatively well-understood spin properties of quantum point contacts in a large in-plane
magnetic field, and are at present applying it to spin measurements of both open and
nearly-isolated quantum dots. The talk will also include a comparison of these
experiments to previous spin measurements of dots and point contacts that have been
performed in this lab and others.