We report on a general theory for analyzing quantum transport through devices in the Metal-QD-Metal configuration where QD is a quantum dot or the device scattering region which contains Rashba spin-orbital and electron-electron interactions. The metal leads may or may not be ferromagnetic, they are assumed to weakly couple to the QD region. Our theory is formulated by second quantizing the Rashba spin-orbital interaction in spectral space (instead of real space), and quantum transport is then analyzed within the Keldysh nonequilibrium Green's function formalism. The Rashba interaction causes two main effects to the Hamiltonian: (i) it gives rise to an extra spin-dependent phase factor in the coupling matrix elements between the leads and the QD; (ii) it gives rise to an inter-level spin-flip term but forbids any intra-level spin-flips. Our formalism provides a starting point for analyzing many quantum transport issues where spin-orbital effects are important. As an example, we investigate transport properties of a Aharnov-Bohm ring in which a QD having Rashba spin-orbital and e-e interactions is located in one arm of the ring. A substantial spin-polarized conductance or current emerges in this device due to a combined effect of a magnetic flux and the Rashba interaction. The direction and strength of the spin-polarization are shown to be controllable by both the magnetic flux and a gate voltage.

We theoretically predict that a pure steady state spincurrent without charge-current can induce an electric field. A formula for the induced electric field is derived and we investigate its characteristics. Conversely, a moving spin is affected by an external electric field and we present a formula for the interaction energy. 72.25.-b, 03.50.De

A spin current is usually carried by electrons and generated due to the imbalance of up-spin and down-spin. Here we investigate another type of spin current, which is carried by magnons. Using nonequilibrium Green'sfunction technique, we have derived a Landauer-Büttiker-type formula for spin current transport. The spin current satisfies conservation condition and can be expressed in terms of the magnon Green's functions of the mesoscopic ferromagnetic isolating system. As an application of this theory, we study the magnon transport properties of a two-level magnon quantum dot in the presence of the magnon-magnon scattering. By solving the self-consistent equations, we obtain the nonlinear spin current as a function of the magnetochemical potential. The spin current generated by using a parametric quantum pumping mechanism is also discussed.

We study proximity-induced superconductivity in gold nanowires as a function of the length of the nanowire, magnetic field, and excitation current. Short nanowires exhibit a sharp superconducting transition, whereas long nanowires show nonzero resistance. At intermediate lengths, however, we observe two sharp transitions; the normal and superconducting regions are separated by what we call the minigap phase. Additionally, we detect periodic oscillations in the differential magnetoresistance. We suggest that the minigap phase as well as the periodic oscillations originate from a coexistence of proximity-induced superconductivity with a normal region near the center of the wire, created either by temperature or the application of a magnetic field.

Deterministic control of magnetization by light, often referred to as all-optical switching (AOS), is an attractive recording method for magnetic nanotechnologies because magnetization control becomes possible without the need of an external magnetic field 7-11 and therefore incorporates the potential for ultra-fast magnetization switching up to 1000 times faster than that by magnetic fields while using lower energies 12 . The first demonstration of the magnetization switching by light was in ferrimangnetic GdFeCo film which is a magneto-optical material 7 where the Gd and FeCo spin sub-lattices are antiferromagnetically exchange coupled. While several mechanisms for the ultrafast magnetization switching of GdFeCo have been explored [14][15][16] , the current understanding for AOS in GdFeCo is that the ultrafast laser excitation demagnetizes the two sublattices at different Hall cross region to measure the evolution of the magnetization to a series of ultrafast laser pulses.We initially used 40 optical pulses for the first two exposure steps, and then, increased to 80 pulses for the next six exposure steps (see methods and given by (N -N)/(N + N). We assume that with each optical pulse there is a switching probability from the spin-up to spin-down state given by P1 and from spin-down to spin-up by P2. The number of FePt grains with spin-up and spin-down states after the n pulses can be expressed by the following:The fitted lines to Eq. What is the origin for different switching probability of P1 and P2 for circularly polarized light pulses? The fact that linear light leads to demagnetization of the sample suggest that heating of the FePt grains by the femto-second laser exposure is sufficient to cause thermal activated reversal.The circularly polarized light then breaks the symmetry of the system favoring one magnetic state 6 over the other and leading to an imbalance in the P1 and P2. This symmetry breaking could result from a direct interaction between the light and the magnetic systems such as the inverse Faraday field that prefers one direction over the other 22 . The difference in P1 and P2 could also arise from differential absorption for RCP and LCP (i.e. magnetic circular dichroism) that will result in a slight difference in temperature for one set of grains compared to the other. 17 We have roughly estimated the difference in temperature needed during the optical excitation to explain the difference in switching probability using a simple Arrhenius-Néel model for single domain particles (see supplementary section for details). A temperature difference of 1-2 K would be sufficient to explain the difference in P1 and P2 observed in Fig. 1, which is consistent with typical dichroism differences in magnetic metals. 17However, independent of the mechanism we find that magnetic switching for granular FePt films is statistical in nature in contrast to the reports on GdFeCo films. Because of this we don't achieve full deterministic switching, which would be needed for magnetic recording applications. To ac...