Spin-orbit coupling and phase-coherence in InAs nanowires

We investigated the magnetotransport of InAs nanowires grown by selective area metal-organic vapor phase epitaxy. In the temperature range between 0.5 and 30 K reproducible fluctuations in the conductance upon variation of the magnetic field or the back-gate voltage are observed, which are attributed to electron interference effects in small disordered conductors. From the correlation field of the magnetoconductance fluctuations the phase-coherence length l_phi is determined. At the lowest temperatures l_phi is found to be at least 300 nm, while for temperatures exceeding 2 K a monotonous decrease of l_phi with temperature is observed. A direct observation of the weak antilocalization effect indicating the presence of spin-orbit coupling is masked by the strong magnetoconductance fluctuations. However, by averaging the magnetoconductance over a range of gate voltages a clear peak in the magnetoconductance due to the weak antilocalization effect was resolved. By comparison of the experimental data to simulations based on a recursive two-dimensional Green's function approach a spin-orbit scattering length of approximately 70 nm was extracted, indicating the presence of strong spin-orbit coupling.Comment: 8 pages, 7 figure

The distance between P680 and QA in Photosystem II determined by ESEEM spectroscopy

AbstractLight induced spin-polarized P680+Q−A radical pairs were studied by two pulse electron spin echo envelope modulation (ESEEM) spectroscopy in the cyanide-treated and Zn-substituted Photosystem II core complexes and in the isolated D1-D2-cyt b559 reaction center complexes reconstituted with dibromoisopropyl-p-benzoquinone. The observed strong out-of phase ESEEM signals were identified as those of the P680+Q−A radical pairs based on the time variation of the transient CW EPR spectra. The shapes of ESEEM spectra were attributed to dipolar D and spin exchange J interactions in the radical pairs. The values of D and J were derived from a sine Fourier transformation and the center-to-center distance between P680 and QA was determined to be 27.2±1.0Å for all three preparations

Low-field magnetoresistance in GaAs 2D holes

We report low-field magnetotransport data in two-dimensional hole systems in GaAs/AlGaAs heterostructures and quantum wells, in a large density range, $2.5 \times 10^{10} \leq p \leq 4.0 \times 10^{11}$ cm$^{-2}$, with primary focus on samples grown on (311)A GaAs substrates. At high densities, $p \gtrsim 1 \times 10^{11}$ cm$^{-2}$, we observe a remarkably strong positive magnetoresistance. It appears in samples with an anisotropic in-plane mobility and predominantly along the low-mobility direction, and is strongly dependent on the perpendicular electric field and the resulting spin-orbit interaction induced spin-subband population difference. A careful examination of the data reveals that the magnetoresistance must result from a combination of factors including the presence of two spin-subbands, a corrugated quantum well interface which leads to the mobility anisotropy, and possibly weak anti-localization. None of these factors can alone account for the observed positive magnetoresistance. We also present the evolution of the data with density: the magnitude of the positive magnetoresistance decreases with decreasing density until, at the lowest density studied ($p = 2.5 \times 10^{10}$ cm$^{-2}$), it vanishes and is replaced by a weak negative magnetoresistance.Comment: 8 pages, 8 figure

Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing

Large-scale molecular simulations are performed to investigate tensile failure of polymer interfaces as a function of welding time $t$. Changes in the tensile stress, mode of failure and interfacial fracture energy $G_I$ are correlated to changes in the interfacial entanglements as determined from Primitive Path Analysis. Bulk polymers fail through craze formation, followed by craze breakdown through chain scission. At small $t$ welded interfaces are not strong enough to support craze formation and fail at small strains through chain pullout at the interface. Once chains have formed an average of about one entanglement across the interface, a stable craze is formed throughout the sample. The failure stress of the craze rises with welding time and the mode of craze breakdown changes from chain pullout to chain scission as the interface approaches bulk strength. The interfacial fracture energy $G_I$ is calculated by coupling the simulation results to a continuum fracture mechanics model. As in experiment, $G_I$ increases as $t^{1/2}$ before saturating at the average bulk fracture energy $G_b$. As in previous simulations of shear strength, saturation coincides with the recovery of the bulk entanglement density. Before saturation, $G_I$ is proportional to the areal density of interfacial entanglements. Immiscibiltiy limits interdiffusion and thus suppresses entanglements at the interface. Even small degrees of immisciblity reduce interfacial entanglements enough that failure occurs by chain pullout and $G_I \ll G_b$

The primary structure of a monoclonal λ-type immunoglobulin L-chain of subgroup II (Bence-Jones protein NEI): Evolutionary origin of antibody variability

ObjectiveThe objective of this study is to assess the gestational age at detection and prevalence of anencephaly in the North of The Netherlands over a 5-year period. MethodsA case list of all cases of anencephaly from two fetal medicine units was compiled. Cases were included if the estimated due date was between 1 August 2008 and 31 July 2013. ResultsOverall prevalence of anencephaly was 5.4 per 10.000 pregnancies (n=110). The majority of cases (69%) was detected before 18 weeks' gestation. Factors determining successful early diagnosis were competence level of the sonographers, with a significantly higher detection rate when scans were performed by a sonographer licensed by the Fetal Medicine Foundation (FMF) for nuchal translucency measurement (p=0.001), and gestational age at or beyond 11weeks of gestation (p=0.024). ConclusionImproving detection of anencephaly in the first trimester requires ultrasound screening at or after 11weeks of gestation, performed by experienced sonographers trained in recognizing fetal anomalies. Sonographers should be instructed that the goal of the first trimester scan is not only to measure nuchal translucency thickness but also to exclude major anomalies. (c) 2015 John Wiley & Sons, Ltd

Clear Spin Valve Signals in Conventional NiFe/ In_<0.75>Ga_<0.25>As-2DEG Hybrid Two-Terminal Structures

We investigated the transport properties of ferromagnetic/semiconductor hybrid two-terminal structures utilizing an In_Ga_As/In_Al_As 2DEG formed on a GaAs (001) substrate with In_xAl_As step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured spin valve properties at low temperatures, and successfully found clear spin valve signals as well as clear channel width dependence. The results with such clear dependence suggest successful spin transport in the present samples

Channel Width Dependence of Spin Polarized Transports in NiFe/InGaAs Hybrid Two-Terminal Structures

We investigated spin polarized transports in NiFe/InGaAs hybrid two-terminal structures at 1.5 K as well as their channel width dependence. The two-terminal structures were fabricated in order to neglect the local Hall effect (LHE) by fringe fields of NiFe contacts. First, we measured magneto-resistance (MR) characteristics of the samples under vertical magnetic fields, and obtained clear oscillations indicating the ohmic formation at NiFe/InGaAs interfaces. Next, we measured spin valve (SV) properties under parallel magnetic fields, and successfully observed clear SV peaks without LHE hysterisis loops. Furthermore, we also confirmed unique behavior of SV peaks depending on the channel width. Such dependence also indicates spin injection/detection through NiFe/InGaAs interfaces