23 research outputs found
Interface dependence of the Josephson-current fluctuations in short SNS junctions
We discuss the dependence of the Josephson current correlations in mesoscopic
superconductor/normal-conductor/superconductor (SNS) devices on the
transparency of the superconductor/normal-conductor (SN) interfaces. Focusing
on short junctions we apply the supersymmetry method to construct an effective
field theory for mesoscopic SNS devices which is evaluated in the limit of
highly and weakly transparent interfaces. We show that the two-point
Josephson-current correlator differs by an universal factor 2 in these two
cases.Comment: 5 pages, 1figure, version accepted by PR
Measurement of Rashba and Dresselhaus spin-orbit magnetic fields
Spin-orbit coupling is a manifestation of special relativity. In the
reference frame of a moving electron, electric fields transform into magnetic
fields, which interact with the electron spin and lift the degeneracy of
spin-up and spin-down states. In solid-state systems, the resulting spin-orbit
fields are referred to as Dresselhaus or Rashba fields, depending on whether
the electric fields originate from bulk or structure inversion asymmetry,
respectively. Yet, it remains a challenge to determine the absolute value of
both contributions in a single sample. Here we show that both fields can be
measured by optically monitoring the angular dependence of the electrons' spin
precession on their direction of movement with respect to the crystal lattice.
Furthermore, we demonstrate spin resonance induced by the spin-orbit fields. We
apply our method to GaAs/InGaAs quantum-well electrons, but it can be used
universally to characterise spin-orbit interactions in semiconductors,
facilitating the design of spintronic devices
Polarisation Patterns and Vectorial Defects in Type II Optical Parametric Oscillators
Previous studies of lasers and nonlinear resonators have revealed that the
polarisation degree of freedom allows for the formation of polarisation
patterns and novel localized structures, such as vectorial defects. Type II
optical parametric oscillators are characterised by the fact that the
down-converted beams are emitted in orthogonal polarisations. In this paper we
show the results of the study of pattern and defect formation and dynamics in a
Type II degenerate optical parametric oscillator for which the pump field is
not resonated in the cavity. We find that traveling waves are the predominant
solutions and that the defects are vectorial dislocations which appear at the
boundaries of the regions where traveling waves of different phase or
wave-vector orientation are formed. A dislocation is defined by two topological
charges, one associated with the phase and another with the wave-vector
orientation. We also show how to stabilize a single defect in a realistic
experimental situation. The effects of phase mismatch of nonlinear interaction
are finally considered.Comment: 38 pages, including 15 figures, LATeX. Related material, including
movies, can be obtained from
http://www.imedea.uib.es/Nonlinear/research_topics/OPO
Anomalous Hall effect in paramagnetic two dimensional systems
We investigate the possibility of observing the anomalous Hall effect (AHE)
in two dimensional paramagnetic systems. We apply the semiclassical equations
of motion to carriers in the conduction and valence bands of wurtzite and
zincblende quantum wells in the exchange field generated by magnetic impurities
and we calculate the anomalous Hall conductivity based on the Berry phase
corrections to the carrier velocity. We show that under certain circumstances
this conductivity approaches one half of the conductance quantum. We consider
the effect of an external magnetic field and show that for a small enough field
the theory is unaltered.Comment: 9 pages, 10 figures, 2 table
Lateral Spin Injection in Germanium Nanowires
Electrical injection of spin-polarized electrons into a semiconductor, large
spin diffusion length, and an integration friendly platform are desirable
ingredients for spin-based devices. Here we demonstrate lateral spin injection
and detection in germanium nanowires, by using ferromagnetic metal contacts and
tunnel barriers for contact resistance engineering. Using data measured from
over 80 samples, we map out the contact resistance window for which lateral
spin transport is observed, manifestly showing the conductivity matching
required for spin injection. Our analysis, based on the spin diffusion theory,
indicates that the spin diffusion length is larger than 100 {\mu}m in germanium
nanowires at 4.2 K
Properties of feedback solitons in a single-mirror experiment
We report on the observation of localized states (LSs) in a single-mirror feedback system using sodium vapor as the nonlinear medium. By combining experimental results with simulations based on a microscopic model and with results of a linear stability analysis of the homogeneous state, we discuss the properties of the LSs, the mechanism of their formation, their domain of existence in parameter space, their interaction with the amplitude and phase gradient in the Gaussian beam of the driving laser, and the formation of 'molecules' and 'clusters' of LSs. We elucidate the dominant role of diffraction in the interaction of the LSs and discuss relations between the clusters of LSs and extended patterns
Haalbaarheidsstudie 2: Recidivemeting forensische zorg. Nader onderzoek naar de ontwikkeling van een recidivemonitor voor de sector forensische zorg
Centraal in deze tweede haalbaarheidsstudie staat de vraag in hoeverre door koppeling van reeds bestaande informatievoorzieningen aan de Justitiële Documentatie uit de OBJD, een betrouwbaar beeld kan worden gegeven van de strafrechtelijke recidive van justitiabelen die vóór 2011 uit één van deze vijf Forensische Zorg-titels zijn uitgestroomd. In de beschrijving van de resultaten wordt onderscheid gemaakt tussen titels die betrekking hebben op forensische zorg tijdens detentie (overbrenging vanuit het gevangeniswezen naar een psychiatrisch ziekenhuis of de hulpverlening) en forensische zorg in het kader van voorwaarden bij een sanctie (voorwaardelijke veroordeling, sepot met voorwaarden en voorwaardelijke invrijheidstelling met bijzondere voorwaarden). Eerste haalbaarheidsstudie (zie link bij: Meer informatie