We study the Kondo effect in a quantum dot which is coupled to ferromagnetic leads and analyse its properties as a function of the spin polarization of the leads. Based on a scaling approach we predict that for parallel alignment of the magnetizations in the leads the strong-coupling limit of the Kondo effect is reached at a finite value of the magnetic field. Using an equation-of-motion technique we study nonlinear transport through the dot. For parallel alignment the zero-bias anomaly may be split even in the absence of an external magnetic field. For antiparallel spin alignment and symmetric coupling, the peak is split only in the presence of a magnetic field, but shows a characteristic asymmetry in amplitude and position.PACS numbers: PACS numbers: 75.20.Hr, 72.15.Qm, 73.23.Hk The Kondo effect [1] in electron transport through a quantum dot (QD) with an odd number of electrons is experimentally well established [2, 3]. Screening of the dot spin due to the exchange coupling with lead electrons yields, at low temperatures, a Kondo resonance. The main goal of the present work is to investigate how ferromagnetic leads influence the Kondo effect. In the extreme case of half-metallic leads, minority-spin electrons are completely absent, i.e., the screening of the dot spin is not possible, and no Kondo-correlated state can form. What happens, however, for the generic case of partially spin polarized leads? How does the spin-asymmetry affect the Kondo effect? Is there still a strong coupling limit, and how are transport properties modified?Based on a poor man's scaling analysis we first show that the strong-coupling limit can still be reached in this case if an external magnetic field is applied. This is familiar from the Kondo effect in QDs with an even number of electrons [4, 5, 6, 7], which occurs at finite magnetic fields, although the physical mechanism is different in the present case. In the second part of the paper we analyze within an equation-of-motion (EOM) approach the nonlinear transport through the QD. We find that for parallel alignment of the lead magnetizations the zerobias anomaly is split. This splitting can be removed by appropriately tuning the strength of an external magnetic field B. In the antiparallel configuration of the lead magnetizations no splitting occurs at zero field.The Anderson Hamiltonian for a QD with a single level at energy ǫ 0 coupled to ferromagnetic leads iswhere c rkσ and d σ are the Fermi operators for electrons with wavevector k and spin σ in the leads, r = L, R, and in the QD, V rk is the tunneling amplitude,, and the last term is the Zeeman energy of the dot. (Stray fields from the leads are neglected.) We assume identical leads and symmetric coupling, V Lk = V Rk . The ferromagnetism of the leads is accounted for by different densities of states (DOS) ν r↑ (ω) and ν r↓ (ω) for up and down-spin electrons.In the following we study the two cases of parallel (P) and antiparallel (AP) alignment of the leads' magnetic moments. For the AP configuration and zero magnetic f...

Conversion of charge current into pure spin current and vice versa in non-magnetic semiconductors or metals, which are called the direct and inverse spin Hall effects (SHEs), provide a new functionality of materials for future spin-electronic architectures. Thus, the realization of a large SHE in a device with a simple and practical geometry is a crucial issue for its applications. Here, we present a multi-terminal device with a Au Hall cross and an FePt perpendicular spin injector to detect giant direct and inverse SHEs at room temperature. Perpendicularly magnetized FePt injects or detects perpendicularly polarized spin current without magnetic field, enabling the unambiguous identification of SHEs. The unprecedentedly large spin Hall resistance of up to 2.9 mOmega is attributed to the large spin Hall angle in Au through the skew scattering mechanism and the highly efficient spin injection due to the well-matched spin resistances of the chosen materials.

Spin injection and accumulation are key phenomena supporting a variety of concepts for spin-electronic devices. These phenomena are expected to be enhanced in nanoparticles over bulk structures due to their discrete energy levels and large charging energies. In this article, precise magnetotransport measurements in the single-electron tunnelling regime are performed by preparing appropriate microfabricated devices containing cobalt nanoparticles. Here we provide experimental evidence for characteristic features of spin accumulation in magnetic nanoparticles, such as oscillations of the magnetoresistance with a periodical sign change as a function of bias voltage. Theoretical analysis of the magnetoresistance behaviour clearly shows that the spin-relaxation time in nanoparticles is highly enhanced in comparison with that in the bulk.

Spin is a fundamental property of electrons, with an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state are essential functions. Coherence of the spin state is a manifestation of its quantum nature, so both the preparation and read-out should be spin-coherent. However, the traditional spin measurement technique based on Kerr rotation, which measures spin population using the rotation of the reflected light polarization that is due to the magneto-optical Kerr effect, requires an extra step of spin manipulation or precession to infer the spin coherence. Here we describe a technique that generalizes the traditional Kerr rotation approach to enable us to measure the electron spin coherence directly without needing to manipulate the spin dynamics, which allows for a spin projection measurement on an arbitrary set of basis states. Because this technique enables spin state tomography, we call it tomographic Kerr rotation. We demonstrate that the polarization coherence of light is transferred to the spin coherence of electrons, and confirm this by applying the tomographic Kerr rotation method to semiconductor quantum wells with precessing and non-precessing electrons. Spin state transfer and tomography offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid.

We study theoretically the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in one-and twodimensions in presence of a Rashba spin-orbit (SO) coupling. We show that rotation of the spin of conduction electrons due to SO coupling causes a twisted RKKY interaction between localized spins which consists of three different terms: Heisenberg, Dzyaloshinsky-Moriya, and Ising interactions. We also show that the effective spin Hamiltonian reduces to the usual RKKY interaction Hamiltonian in the twisted spin space where the spin quantization axis of one localized spin is rotated.There has been a great deal of interest in the field of spintronics where spin degrees of freedom of electrons are manipulated to produce a desirable outcome 1,2 . Eminent examples are given by the giant magnetoresistance (GMR) effect 3,4,5 and the interlayer exchange coupling in magnetic multilayers 6,7,8 . The interlayer exchange coupling is explained in the context of Ruderman-KittelKasuya-Yosida (RKKY) interaction 9,10 , equivalently, or in terms of spin-dependent electron confinement 11,12 . The RKKY interaction is an indirect exchange interaction between two localized spins via the spin polarization of conduction electrons 13,14,15,16 .Recently, much attention has been focused on the effect of the Rashba spin-orbit (SO) coupling in twodimensional electron gases (2DEG) 17 . Investigation of the Rashba effect of 2DEG in semiconductor heterostructures has been stimulated by the proposition of a spin field effect transistor 18 . It has been established the Rashba SO coupling can be controlled by means of a gate voltage 19,20,21,22 . The Rashba effect has also been observed in 2DEG formed from surface states electrons at metal surfaces such as Au (111) 23,24,25,26,27 , Li/W(110) or Li/Mo(110) 28 . It has also been found that confinement of the surface state due to atomic steps on vicinal surfaces leads to quasi one-dimensional (1D) surface states, which also exhibit the Rashba effect 29,30,31 .Usually the RKKY interaction yields a parallel or antiparallel coupling of localized spins (Heisenberg coupling). However, if spin of conduction electrons precesses due to the spin-orbit coupling, it can be possible to produce a non-collinear Dzyaloshinsky-Moriya (DM) coupling of localized spins 32,33,34 . In this paper, we investigate the RKKY coupling between localized spins embedded in a 1D-or 2DEG with Rashba SO coupling. We show that rotation of the spin of conduction electrons due to the Rashba SO coupling causes a twisted RKKY interaction between localized spins which consists of three different terms: Heisenberg, Dzyaloshinsky-Moriya, and Ising interactions. We point out that a perturbative treatment of the SO coupling as is usually done 32,33,34 is valid only for small distances between the localized spins; in this case the DM and Ising terms are respectively linear and quadratic with respect to the SO coupling strength. In the limit of large distances, a non-perturbative treatment of the SO coupling is necessary, and one obtains DM and Ising terms...

The purification process of an antibody in manufacturing involves temporal exposure of the molecules to low pH followed by neutralization-pH-shift stress-which causes aggregation. It remains unclear how aggregation triggered by pH-shift stress grows at neutral pH and how it depends on the temperature in an ambient range. We used static and dynamic light scattering to monitor the time-dependent evolution of the aggregate size of the pH-shift stressed antibody between 4.0 and 40.0 °C. A power-law relationship between the effective molecular weight and the effective hydrodynamic radius was found, indicating that the aggregates were fractal with a dimension of 1.98. We found that the aggregation kinetics in the lower-temperature range, 4.0-25.0 °C, were well described by the Smoluchowski aggregation equation. The temperature dependence of the effective aggregation rate constant gave 13 ± 1 kcal/mol of endothermic activation energy. Temporal acid exposure creates an enriched population of unfolded protein molecules that are competent of aggregating. Therefore, the energetically unfavorable unfolding step is not required and the aggregation proceeds faster. These findings provide a basis for predicting the growth of aggregates during storage under practical, ambient conditions.

We theoretically study the electron transport through a magnetic point contact (PC) with special attention given to the effect of an atomic scale domain wall (DW). The spin precession of a conduction electron is forbidden in such an atomic scale DW and the sequence of quantized conductances depends on the relative orientation of magnetizations between left and right electrodes. The magnetoresistance is strongly enhanced for the narrow PC and oscillates with the conductance.

Extensive resection, mainly extended right hemihepatectomy, after biliary drainage and preoperative portal vein embolization, when necessary, for patients with hilar bile duct cancer can be performed safely and is more likely to result in histologically negative margins than other resection methods.