PACS. 72.15.Rn -Localization effects (Anderson or weak localization). PACS. 71.27.+a -Strongly correlated electron systems; heavy fermions. PACS. 71.30.+h -Metal-insulator transitions and other electronic transitions.Abstract. -We present a self-consistent theory of Anderson localization that yields a simple algorithm to obtain typical local density of states as an order parameter, thereby reproducing the essential features of a phase-diagram of localization-delocalization quantum phase transition in the standard lattice models of disordered electron problem. Due to the local character of our theory, it can easily be combined with dynamical mean-field approaches to strongly correlated electrons, thus opening an attractive avenue for a genuine non-perturbative treatment of the interplay of strong interactions and strong disorder.c EDP Sciences

We study two-terminal devices for DNA sequencing which consist of a metallic graphene nanoribbon with zigzag edges (ZGNR) and a nanopore in its interior through which the DNA molecule is translocated. Using the nonequilibrium Green functions combined with density functional theory, we demonstrate that each of the four DNA nucleobases inserted into the nanopore, whose edge carbon atoms are passivated by either hydrogen or nitrogen, will lead to a unique change in the device conductance. Unlike other recent biosensors based on transverse electronic transport through translocated DNA, which utilize small (of the order of pA) tunneling current across a nanogap or a nanopore yielding a poor signal-to-noise ratio, our device concept relies on the fact that in ZGNRs local current density is peaked around the edges so that drilling a nanopore away from the edges will not diminish the conductance. Inserting a nucleobase into the nanopore affects the charge density in the surrounding area, thereby modulating edge conduction currents whose magnitude is of the order of μA at bias voltage ≃ 0.1 V. The proposed biosensors are not limited to ZGNRs and they could be realized with other nanowires supporting transverse edge currents, such as chiral GNRs or wires made of two-dimensional topological insulators.

Three-dimensional (3D) topological insulators are known for their strong spin-orbit coupling (SOC) and the existence of spin-textured surface states that might be potentially exploited for "topological spintronics." Here, we use spin pumping and the inverse spin Hall effect to demonstrate successful spin injection at room temperature from a metallic ferromagnet (CoFeB) into the prototypical 3D topological insulator Bi2Se3. The spin pumping process, driven by the magnetization dynamics of the metallic ferromagnet, introduces a spin current into the topological insulator layer, resulting in a broadening of the ferromagnetic resonance (FMR) line width. Theoretical modeling of spin pumping through the surface of Bi2Se3, as well as of the measured angular dependence of spin-charge conversion signal, suggests that pumped spin current is first greatly enhanced by the surface SOC and then converted into a dc-voltage signal primarily by the inverse spin Hall effect due to SOC of the bulk of Bi2Se3. We find that the FMR line width broadens significantly (more than a factor of 5) and we deduce a spin Hall angle as large as 0.43 in the Bi2Se3 layer.

We demonstrate that flow of longitudinal unpolarized current through a ballistic two-dimensional electron gas with Rashba spin-orbit coupling will induce nonequilibrium spin accumulation which has opposite sign for the two lateral edges and it is, therefore, the principal observable signature of the spin Hall effect in two-probe semiconductor nanostructures. The magnitude of its out-ofplane component is gradually diminished by static disorder, while it can be enhanced by an in-plane transverse magnetic field. Moreover, our prediction of the longitudinal component of the spin Hall accumulation, which is insensitive to the reversal of the bias voltage, offers a smoking gun to differentiate experimentally between the extrinsic, intrinsic, and mesoscopic spin Hall mechanisms.PACS numbers: 72.25. Dc, 85.75.Nn Introduction-When electric current flows along a conductor subjected to a perpendicular magnetic field, the Lorenz force deflects the charge carriers creating a transverse Hall voltage between the lateral edges of the sample. The normal Hall effect is one of the most familiar phenomena, as well as a widely utilized tool, in condensed matter physics [1]. In the absence of external magnetic field, more esoteric Hall-type effects involving electron spin become possible in paramagnetic systems with spinorbit (SO) couplings-the opposite spins can be separated and then accumulated on the lateral edges when they are transported by a pure (i.e., not accompanied by any net charge current) spin Hall current flowing in the transverse direction in response to unpolarized charge current in the longitudinal direction. For instance, the SO dependent scattering off impurities, which deflects spin-↑ and spin-↓ electrons of an unpolarized beam in opposite directions, and it is partially responsible for the anomalous Hall effect in ferromagnetic metals [1], has been invoked in early studies to predict the extrinsic (i.e., due to impurity scattering) spin Hall effect [2].

We predict that unpolarized charge current driven through the longitudinal leads attached to ballistic quantum-coherent two-dimensional electron gas (2DEG) in semiconductor heterostructure will induce a pure spin current, which is not accompanied by any net charge flow, in the transverse voltage probes. Its magnitude can be tuned by the Rashba spin-orbit (SO) interaction and, moreover, it is resilient to weak spin-independent scattering off impurities within the metallic diffusive regime. While the polarization vector of the spin transported through the transverse leads is not orthogonal to the plane of 2DEG, we demonstrate that only two components (out-of-plane and longitudinal) of the transverse spin current are signatures of the spin Hall effect in four-probe Rashba spin-split semiconductor nanostructures. The linear response spin Hall current, obtained from the multiprobe Landauer-Büttiker scattering formalism generalized for quantum transport of spin, is the Fermi-surface determined nonequilibrium quantity whose scaling with the 2DEG size L reveals the importance of processes occurring on the spin precession mesoscale LSO (on which spin precesses by an angle π)-the out-of-plane component of the transverse spin current exhibits quasioscillatory behavior for L LSO (attaining the maximum value in 2DEGs of the size LSO × LSO), while it reaches the asymptotic value in the macroscopic regime L ≫ LSO. Furthermore, these values of the spin Hall current can be manipulated by the measuring geometry defined by the attached leads.