Observations of discrete magnetosonic waves off the magnetic equator

Fast mode magnetosonic waves are typically confined close to the magnetic equator and exhibit harmonic structures at multiples of the local, equatorial proton cyclotron frequency. We report observations of magnetosonic waves well off the equator at geomagnetic latitudes from −16.5°to −17.9° and L shell ~2.7–4.6. The observed waves exhibit discrete spectral structures with multiple frequency spacings. The predominant frequency spacings are ~6 and 9 Hz, neither of which is equal to the local proton cyclotron frequency. Backward ray tracing simulations show that the feature of multiple frequency spacings is caused by propagation from two spatially narrow equatorial source regions located at L ≈ 4.2 and 3.7. The equatorial proton cyclotron frequencies at those two locations match the two observed frequency spacings. Our analysis provides the first observations of the harmonic nature of magnetosonic waves well away from the equatorial region and suggests that the propagation from multiple equatorial sources contributes to these off-equatorial magnetosonic emissions with varying frequency spacings

Exciton spin dynamics in spherical CdS quantum dots

Exciton spin dynamics in quasi-spherical CdS quantum dots is studied in detail experimentally and theoretically. Exciton states are calculated using the 6-band k.p Hamiltonian. It is shown that for various sets of Luttinger parameters, when the wurtzite lattice crystal field splitting and Coulomb interaction between the electron-hole pair are taken into account exactly, both the electron and hole wavefunction in the lowest exciton state are of S-type. This rules out the spatial-symmetry-induced origin of the dark exciton in CdS quantum dots. The exciton bleaching dynamics is studied using time- and polarization-resolved transient absorption technique of ultrafast laser spectroscopy. Several samples with a different mean size of CdS quantum dots in different glass matrices were investigated. This enabled the separation of effects that are typical for one particular sample from those that are general for this type of material. The experimentally determined dependence of the electron spin relaxation rate on the radius of quantum dots agrees well with that computed theoretically.Comment: 24 pages, 10 figure

Femtosecond control of electric currents at the interfaces of metallic ferromagnetic heterostructures

The idea to utilize not only the charge but also the spin of electrons in the operation of electronic devices has led to the development of spintronics, causing a revolution in how information is stored and processed. A novel advancement would be to develop ultrafast spintronics using femtosecond laser pulses. Employing terahertz (10$^{12}$ Hz) emission spectroscopy, we demonstrate optical generation of spin-polarized electric currents at the interfaces of metallic ferromagnetic heterostructures at the femtosecond timescale. The direction of the photocurrent is controlled by the helicity of the circularly polarized light. These results open up new opportunities for realizing spintronics in the unprecedented terahertz regime and provide new insights in all-optical control of magnetism.Comment: 3 figures and 2 tables in the main tex

A survey of haptics in serious gaming

Serious gaming often requires high level of realism for training and learning purposes. Haptic technology has been proved to be useful in many applications with an additional perception modality complementary to the audio and the vision. It provides novel user experience to enhance the immersion of virtual reality with a physical control-layer. This survey focuses on the haptic technology and its applications in serious gaming. Several categories of related applications are listed and discussed in details, primarily on haptics acts as cognitive aux and main component in serious games design. We categorize haptic devices into tactile, force feedback and hybrid ones to suit different haptic interfaces, followed by description of common haptic gadgets in gaming. Haptic modeling methods, in particular, available SDKs or libraries either for commercial or academic usage, are summarized. We also analyze the existing research difficulties and technology bottleneck with haptics and foresee the future research directions

Magneto-Seebeck microscopy of domain switching in collinear antiferromagnet CuMnAs

Antiferromagnets offer spintronic device characteristics unparalleled in ferromagnets owing to their lack of stray fields, THz spin dynamics, and rich materials landscape. Microscopic imaging of antiferromagnetic domains is one of the key prerequisites for understanding physical principles of the device operation. However, adapting common magnetometry techniques to the dipolar-field-free antiferromagnets has been a major challenge. Here we demonstrate in a collinear antiferromagnet a thermoelectric detection method by combining the magneto-Seebeck effect with local heat gradients generated by scanning far-field or near-field techniques. In a 20-nm epilayer of uniaxial CuMnAs we observe reversible 180∘ switching of the Néel vector via domain wall displacement, controlled by the polarity of the current pulses. We also image polarity-dependent 90∘ switching of the Néel vector in a thicker biaxial film, and domain shattering induced at higher pulse amplitudes. The antiferromagnetic domain maps obtained by our laboratory technique are compared to measurements by the established synchrotron-based technique of x-ray photoemission electron microscopy using x-ray magnetic linear dichroism