The controlled creation, manipulation and detection of spin-polarized currents by purely electrical means remains a central challenge of spintronics. Efforts to meet this challenge by exploiting the coupling of the electron orbital motion to its spin, in particular Rashba spin-orbit coupling, have so far been unsuccessful. Recently, it has been shown theoretically that the confining potential of a small current-carrying wire with high intrinsic spin-orbit coupling leads to the accumulation of opposite spins at opposite edges of the wire, though not to a spin-polarized current. Here, we present experimental evidence that a quantum point contact -- a short wire -- made from a semiconductor with high intrinsic spin-orbit coupling can generate a completely spin-polarized current when its lateral confinement is made highly asymmetric. By avoiding the use of ferromagnetic contacts or external magnetic fields, such quantum point contacts may make feasible the development of a variety of semiconductor spintronic devices.

We have measured the magnetic splitting Delta K of a Kondo peak in the differential conductance of a single-electron transistor while tuning the Kondo temperature T K along two different paths in parameter space: varying the dot-lead coupling at a constant dot energy and vice versa. At a high magnetic field B, the changes of DeltaK with TK along the two paths have opposite signs, indicating that Delta K is not a universal function of TK. At low B, we observe a decrease in DeltaK with TK along both paths, in agreement with theoretical predictions. Furthermore, we find Delta K/Delta<1 at low B and Delta K/Delta>1 at high B, where Delta is the Zeeman energy of the bare spin, in the same system.

Random percolative disorder has been introduced into 300x300 arrays of Nb-Au-Nb proximitycoupled junctions. Our measurements of dc transport properties show that large amounts of random disorder, although depressing Tc and broadening the resistive transition, do not alter the scale invariance of the phase transition. These results are described by a model which rescales the Josephson lattice by the percolation correlation length. The relevance of the observations to granular thin films is discussed.

We study of the appearance and evolution of several anomalous (i.e., G < G(0) D 2e(2)/h) conductance plateaus in an In(0.52)Al(0.48)As/InAs quantum point contact (QPC). This work was performed at T = 4:2 K as a function of the offset bias ΔV(G) between the two in-plane gates of the QPC. The number and location of the anomalous conductance plateaus strongly depend on the polarity of the offset bias. The anomalous plateaus appear only over an intermediate range of offset bias of several volts. They are quite robust, being observed over a maximum range of nearly 1 V for the common sweep voltage applied to the two gates. These results are interpreted as evidence for the sensitivity of the QPC spin polarization to defects (surface roughness and impurity (dangling bond) scattering) generated during the etching process that forms the QPC side walls. This assertion is supported by non-equilibrium Green function simulations of the conductance of a single QPC in the presence of dangling bonds on its walls. Our simulations show that a spin conductance polarization as high as 98% can be achieved despite the presence of dangling bonds. The maximum in is not necessarily reached where the conductance of the channel is equal to 0:5G(0).

The appearance and evolution of an anomalous conductance plateau at 0.4(2e2/h) in an In0.52Al0.48As/InAs quantum point contact (QPC), in the presence of lateral spin-orbit coupling, has been studied at T = 4.2 K as a function of the potential asymmetry between the in-plane gates of the QPC. The anomalous plateau, a signature of spin polarization in the channel, appears only over an intermediate range (around 3 V) of bias asymmetry. It is quite robust, being observed over a maximum range of nearly 1 V of the sweep voltage common to the two in-plane gates. The conductance measurements show evidence of surface roughness and dangling bond scattering from the side walls of the QPC.