Search results for " Polarization"
showing 10 items of 668 documents
Anisotropic polarization of non‐polar GaN quantum dot emission
2009
We report on experimental and theoretical studies of the polarization selection rules of the emission of non-polar GaN/AlN self-assembled quantum dots. Time-integrated and time-resolved photoluminescence measurements have been performed to determine the degree of polarization. It is found that the emission of some samples can be predominantly polarized parallel to the wurtzite c axis, in striking difference with the previously reported results for bulk GaN and its heterostructures, in which the emission was preferentially polarized perpendicular to the c axis. Theoretical calculations based on an 8-band k·p model are used to analyze the relative importance of strain, confinement and quantum…
New Materials with High Spin Polarization Investigated by X-Ray Magnetic Circular Dichroism
2013
We investigate element-specific spin and orbital magnetic moments of polycrystalline bulk Heusler alloys that are predicted to be half-metallic with composition Co2YZ (Y = Ti, Cr, Mn, Fe and Z = Al, Ga, Si, Ge, Sn, Sb) using magnetic circular dichroism in X-ray absorption spectroscopy (XAS/XMCD). In addition to stoichiometric compounds we also investigate composition series with partly replaced elements on the Y-site (Co2Fe x Cr1−x Si, Co2Mn x Ti1−x Si and Co2Mn x Ti1−x Ge) and on the Z-site (Co2MnGa1−x Ge x ) promising a tailoring of the Fermi level with respect to the minority band gap. We compare experimental results with theoretical predictions elucidating the influence of local disorde…
Polarization detection of trapped electrons via interaction with polarized atoms
1971
Electrons were trapped in an electrostatic quadrupole trap with superimposed homogeneous magnetic field. The electrons were polarized by spin exchange with a polarized atomic beam. The free trapped electron polarization was converted to a change in the electron translational energy via spin-dependent inelastic collisions with the atomic beam, and the electron translational temperature was monitored. Discussed are the development of this variation of the measurement technique, characteristics of electron storage, and the electron-polarized atom inelastic interaction as a function of electron temperature and time. The method has been applied to the detection of the (g-2) resonance of free, st…
Influence of strain in the reduction of the internal electric field in GaN/AlN quantum dots grown ona-plane 6H-SiC
2006
The strain state of stacks of GaN/AIN quantum dots (QDs) grown on (0001) and (1120) 6H-SiC has been investigated by means of Raman spectroscopy. Depending on the orientation of the wurtzite axis with respect to the growth direction it is found that the piezoelectric contribution to the electrostatic potential may either reinforce that arising from the spontaneous polarization or oppose it. The experimental results are compared with a theoretical model for the strain and polarization field in QDs of both orientations that allows the calculation of the electrostatic potential in the QDs. Both the experimental results and the theoretical model indicate that the internal electric field and elec…
Deviations from Kleinman symmetry of the second-order polarizability tensor in molecules with low-lying perpendicular electronic bands
1993
Abstract 4-Nitroaniline (pNA) and 3,5-dinitro-aniline (3,5-DNA) were studied by electric field induced second harmonic generation (EFISH) and electrooptical absorption measurements (EOAM) in dioxane solution at T = 298 K. The measurements were carried out for two polarization conditions, the electric field vector of the linearly polarized incident light being parallel or perpendicular to the static electric field. The second-order polarizability tensor of pNA is confirmed to be Kleinman symmetric, while a strong deviation from index permutation symmetry is observed for 3,5-DNA. The latter is quantitatively interpreted by contributions of a low-lying electronic band with transition dipole pe…
Spin-polarization effects for electrons passing through thin iron and cobalt films
1993
Abstract Spin-dependent effects of the inelastic mean free path (IMFP) are evident for low-energy electrons passing through magnetized ferromagnetic films caused by a different attenuation within the layer. Values of IMFP for both spin components were determined for ultrathin iron and cobalt layers on W(1 1 0) by means of spin-resolving photoelectron spectroscopy.
Spin-Wave Driven Bidirectional Domain Wall Motion in Kagome Antiferromagnets
2021
We predict a mechanism to controllably manipulate domain walls in kagome antiferromagnets via a single linearly polarized spin-wave source. We show by means of atomistic spin dynamics simulations of antiferromagnets with kagome structure that the speed and direction of the domain wall motion can be regulated by only tuning the frequency of the applied spin-wave. Starting from microscopics, we establish an effective action and derive the corresponding equations of motion for the spin-wave-driven domain wall. Our analytical calculations reveal that the coupling of two spin-wave modes inside the domain wall explains the frequency-dependent velocity of the spin texture. Such a highly tunable sp…
Ferromagnetic Coupling through Spin Polarization in a Dinuclear Copper(II) Metallacyclophane.
2001
[DT] Von organischen Radikalen zu Metallkomplexen konnte das bekannte Konzept für Ferroelektrika erfolgreich ausgedehnt werden: Die Abbildung zeigt ein Cyclophan-artiges Molekül mit einem Triplett-Grundzustand, in dem zwei CuII-Zentren von einem doppelten m-Phenylendiamid-Gerüst zusammengehalten werden.
Rotational Raman spectroscopy of ethylene using a femtosecond time-resolved pump-probe technique.
2005
154309; Femtosecond Raman-induced polarization spectroscopy (RIPS) was conducted at low pressure (250 mb at 295 K and 400 mb at 373 K) in ethylene. The temporal signal, resulting from the beating between pure rotational coherences, was measured with a heterodyne detection. The temporal traces were converted to the frequency domain using a Fourier transformation and then analyzed thanks to the D2hTDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html) dedicated to X2Y4 molecules with D2h symmetry. The effective Hamiltonian was expanded up to order 2, allowing the determination of five parameters with an rms of 0.017 cm(-1). Special care was taken in the precise modeling of intensities, taki…
Polarization-domain-wall complexes in fiber lasers
2013
To study the possible build-up of polarization-domain-walls (PDWs) in fiber laser cavities, an erbium-doped fiber ring laser was used and a wide range of vector polarization dynamics that can be selected at a given pump power, by using the degrees of freedom of two intracavity polarization controllers (PC) was investigated. A simple theoretical model that explains polarization switching in fiber ring lasers featuring a normally dispersive cavity with a typical, moderate, level of birefringence is presented. Such polarization dynamics, based on a special class of polarization-domain-wall structures, agrees qualitatively well with experimental observations. The paper stresses on the complex a…