Simulations of spin filtering effects in a quantum point contact

In this paper, we review the results of transport simulations that we have done in recent years, of quantum point contacts (QPCs) which incorporate spin-density-functional theory. Besides the usual plateaus at integer multiples of G₀ = (2e²/h) our calculations yield the type of ∼0.7G₀ features that have now become familiar in experiment, as well as anomalies at other non-integer values. These features appear to be correlated with the formation of an energy barrier structure within the QPC that can be very strongly spin dependent. In particular, these can be strong enough that there are circumstances where two spin-down modes may pass through the QPC before any current from the other spin orientation is allowed through. The barriers can be tuned to produce different spin filtering effects and can lead to the formation of a local magnetic moment in the QPC region, which however is only weakly confined in our case. We can also account for the absence of plateaus at higher integer values of G₀.