Spin Hall Effect and Spin Transfer in Disordered Rashba Model

Based on numerical study of the Rashba model, we show that the spin Hall conductance remains finite in the presence of disorder up to a characteristic length scale, beyond which it vanishes exponentially with the system size. We further perform a Laughlin's gauge experiment numerically and find that all energy levels cannot cross each other during an adiabatic insertion of the flux in accordance with the general level-repulsion rule. It results in zero spin transfer between two edges of the sample as each state always evolves back after the insertion of one flux quantum, in contrast to the quantum Hall effect. It implies that the topological spin Hall effect vanishes with the turn-on of disorder.Comment: 4 pages, 4 figures final versio

Quantum Spin Hall Effect and Topologically Invariant Chern Numbers

We present a topological description of quantum spin Hall effect (QSHE) in a two-dimensional electron system on honeycomb lattice with both intrinsic and Rashba spin-orbit couplings. We show that the topology of the band insulator can be characterized by a $2\times 2$ traceless matrix of first Chern integers. The nontrivial QSHE phase is identified by the nonzero diagonal matrix elements of the Chern number matrix (CNM). A spin Chern number is derived from the CNM, which is conserved in the presence of finite disorder scattering and spin nonconserving Rashba coupling. By using the Laughlin's gedanken experiment, we numerically calculate the spin polarization and spin transfer rate of the conducting edge states, and determine a phase diagram for the QSHE.Comment: 4 pages and 4 figure

Phase diagram of the frustrated, spatially anisotropic S=1 antiferromagnet on a square lattice

We study the S=1 square lattice Heisenberg antiferromagnet with spatially anisotropic nearest neighbor couplings $J_{1x}$, $J_{1y}$ frustrated by a next-nearest neighbor coupling $J_{2}$ numerically using the density-matrix renormalization group (DMRG) method and analytically employing the Schwinger-Boson mean-field theory (SBMFT). Up to relatively strong values of the anisotropy, within both methods we find quantum fluctuations to stabilize the N\'{e}el ordered state above the classically stable region. Whereas SBMFT suggests a fluctuation-induced first order transition between the N\'{e}el state and a stripe antiferromagnet for $1/3\leq J_{1x}/J_{1y}\leq 1$ and an intermediate paramagnetic region opening only for very strong anisotropy, the DMRG results clearly demonstrate that the two magnetically ordered phases are separated by a quantum disordered region for all values of the anisotropy with the remarkable implication that the quantum paramagnetic phase of the spatially isotropic $J_{1}$-$J_{2}$ model is continuously connected to the limit of decoupled Haldane spin chains. Our findings indicate that for S=1 quantum fluctuations in strongly frustrated antiferromagnets are crucial and not correctly treated on the semiclassical level.Comment: 10 pages, 10 figure

Effect of different implant placement depths on crestal bone levels and soft tissue behavior: A 5â year randomized clinical trial

ObjectivesThis randomized clinical trial analyzed the longâ term (5â year) crestal bone changes and soft tissue dimensions surrounding implants with an internal tapered connection placed in the anterior mandibular region at different depths (equiâ and subcrestal).Materials and methodsEleven edentulous patients were randomly divided in a splitâ mouth design: 28 equicrestal implants (G1) and 27 subcrestal (1â 3 mm) implants (G2). Five implants were placed per patient. All implants were immediately loaded. Standardized intraoral radiographs were used to evaluate crestal bone (CB) changes. Patients were assessed immediately, 4, 8, and 60 months after implant placement. The correlation between vertical mucosal thickness (VMT) and soft tissue recession was analyzed. Subâ group analysis was also performed to evaluate the correlation between VMT and CB loss. Rankâ based ANOVA was used for comparison between groups (α = .05).ResultsFiftyâ five implants (G1 = 28 and G2 = 27) were assessed. Implant and prosthetic survival rate were 100%. Subcrestal positioning resulted in less CB loss (â 0.80 mm) when compared to equicrestal position (â 0.99 mm), although the difference was not statistically significant (p > .05). Significant CB loss was found within the G1 and G2 groups at two different measurement times (T4 and T60) (p  .05).ConclusionsThere was no statistically significant difference in CB changes between subcrestal and equicrestal implant positioning; however, subcrestal position resulted in higher bone levels. Neither mucosal recession nor vertical mucosa thickness was influenced by different implant placement depths.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154286/1/clr13569.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154286/2/clr13569_am.pd

Magnetoelastic effects and random magnetic anisotropy in highly strained ultrathin Ni nanowires epitaxied in a SrTiO3 matrix

International audienceWe analyze the magnetic anisotropy of Ni nanowires with diameters smaller than 5 nm. The nanowires are vertically epitaxied in a SrTiO 3 (001) matrix which generates huge tensile strains up to 3.6% along the nanowire axis. This leads to an unusual anisotropy, characterized by an easy magnetization plane perpendicular to the nanowire axis. Hysteresis cycles M(H) unveil an overall in-plane isotropy, while an opening of the M(H) cycles and thermal activation measurements indicate the presence of local energy barriers inside the nanowires. Surprisingly, the coercive field H c (T) decays exponentially with increasing temperature, for both the easy plane and the hard axis. Based on these findings, we provide an analysis of magnetoelastic effects in the nanowires. By considering global averaging over the anisotropy distribution and local averaging according to the Random Magnetic Anisotropy model, we find that the global anisotropy, with its hard axis and isotropic easy plane, is related to the mean strain, while coercivity arises from local strain variations. We evidence that a thermally activated anisotropy softening occurs in the nanowires, in addition to Sharrock's law of thermal reduction of coercivity. Possible mechanisms responsible for this thermal softening of anisotropy are proposed and discussed. Our study eventually allows to identify two major competing effects at play in the present system: an increasing magnetic anisotropy with increasing strain and a reduction of the anisotropy with increasing local strain fluctuations

Highly selective population of spin-orbit levels in electronic autoionization of O₂

The dynamics of electronic autoionization in O2 has been studied using a new apparatus which combines a free-jet supersonic expansion with synchrotron radiation. Ions and electrons were analyzed by a double time-of-flight spectrometer. The spin-orbit sublevels of the 3Πu (v=0 and 2) Rydberg states in O2 were selectively excited and the resulting O+2 final states were determined by time-of-flight photoelectron spectros copy. A strong variation of the 2Π1/2g :2Π3/2g branching ratio was observed. This variation results from the selection of a single continuum wave function in the autoionization process

Magnetic Incommensurability in Doped Mott Insulator

In this paper we explore the incommensurate spatial modulation of spin-spin correlations as the intrinsic property of the doped Mott insulator, described by the $t-J$ model. We show that such an incommensurability is a direct manifestation of the phase string effect introduced by doped holes in both one- and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin susceptibility in momentum space are in agreement with the neutron-scattering measurement of cuprate superconductors in both position and doping dependence. In particular, this incommensurate structure can naturally reconcile the neutron-scattering and NMR experiments of cuprates.Comment: 12 pages (RevTex), five postscript figure

Spin-charge separation in the single hole doped Mott antiferromagnet

The motion of a single hole in a Mott antiferromagnet is investigated based on the t-J model. An exact expression of the energy spectrum is obtained, in which the irreparable phase string effect [Phys. Rev. Lett. 77, 5102 (1996)] is explicitly present. By identifying the phase string effect with spin backflow, we point out that spin-charge separation must exist in such a system: the doped hole has to decay into a neutral spinon and a spinless holon, together with the phase string. We show that while the spinon remains coherent, the holon motion is deterred by the phase string, resulting in its localization in space. We calculate the electron spectral function which explains the line shape of the spectral function as well as the ``quasiparticle'' spectrum observed in angle-resolved photoemission experiments. Other analytic and numerical approaches are discussed based on the present framework.Comment: 16 pages, 9 figures; references updated; to appear in Phys. Rev.

Mean-Field Description of Phase String Effect in the t−Jt-J Model

A mean-field treatment of the phase string effect in the $t-J$ model is presented. Such a theory is able to unite the antiferromagnetic (AF) phase at half-filling and metallic phase at finite doping within a single theoretical framework. We find that the low-temperature occurrence of the AF long range ordering (AFLRO) at half-filling and superconducting condensation in metallic phase are all due to Bose condensations of spinons and holons, respectively, on the top of a spin background described by bosonic resonating-valence-bond (RVB) pairing. The fact that both spinon and holon here are bosonic objects, as the result of the phase string effect, represents a crucial difference from the conventional slave-boson and slave-fermion approaches. This theory also allows an underdoped metallic regime where the Bose condensation of spinons can still exist. Even though the AFLRO is gone here, such a regime corresponds to a microscopic charge inhomogeneity with short-ranged spin ordering. We discuss some characteristic experimental consequences for those different metallic regimes. A perspective on broader issues based on the phase string theory is also discussed.Comment: 18 pages, five figure