High frequency fast magnetoacoustic modes in the plasma core

Fast magnetoacoustic modes (FMM) [known also as compressional Alfvén eigenmodes (CAE) and magnetosonic modes] with frequencies exceeding or equal the ion gyrofrequency are considered. It is shown that edge-localized FMM, which presumably are responsible for the superthermal ion cyclotron emission (ICE) observed in many experiments on tokamaks and stellarators, represent a particular case of these modes. In general, FMMs with frequencies above/about the ion gyrofrequency have different radial locations and structures. They can extend over a large part of the plasma cross section and even can have maximum amplitudes at the magnetic axis. Modes with the same frequency and the same poloidal mode number are multiple, having different radial structures. These results are obtained in the approximation of cylindrical plasma with one-ion species.     

High frequency intrinsic modes in El Niño/Southern Oscillation Index

Recent daily data of the Southern Oscillation Index have been analyzed. The power spectrum indicates major intrinsic geophysical short periods. We find interesting “high frequency” oscillations at 24, 27, 37, 76, 100 and 365 days. In particular the 24 days peaks may correspond to the Branstator-Kushnir wave, the 27 days may be due to the moon effect rotation, the 37 days peaks are most probably related to the Madden and Julian Oscillation. It is not yet clear the explanations for the 76 days which may be associated with interseasonal oscillation in the tropical atmosphere; the 100 days could be resulting from a mere beat between the 37 and 27 periods, or the 76 and 365 days. We use these periods to reconstruct the signal and to produce a forecast for the next 9 months, at the time of writing. After cleansing the signal of those periodicities a detrended fluctuation analysis is performed to reveal the nature of the stochastic structures in the signal and whether specific correlation can be found. We study the evolution of the distribution of first return times, in particular between extreme events. A markedly significant difference from the expected distribution for uncorrelated events is found.     

High frequency local modes,superconductivity and anomalous isotope effect in PdH(D) systems

The possible mechanisms of enhanced superconductivity in PdH(D) systems are discussed. It is concluded that quenching of paramagnons due to reduced coulomb pseudopotentialalone cannot account for the highT _c observed in these systems. Possible participation of the high frequency optic phonon band in BCS-type interaction could lead to a highT _c and an opposite isotope effect in these systems. The possibility of the occurrence of some high-q soft modes due to large lattice expansion in these systems to yieldT _c ～9 K requires about 2-fold softing of the effective Pd-Pd force constant in PdH compared to that in metallic Pd.     

Interferometric selection of frequency comb modes

We demonstrate a scheme to split an optical frequency comb into four separate frequency combs, each with four times the repetition rate of the original, but which are offset in frequency from each other. These spectrally rarified “daughter” combs are generated using fibre interferometers that are actively stabilised. We describe how these “daughter” combs can be used to resolve ambiguities that occur when comparing an arbitrary frequency continuous-wave signal against an optical frequency comb.     

Electrical manipulation of nanomagnets

We demonstrate that it is possible to manipulate the magnetic coupling between two nanomagnets by means of an ac electric field. In the scheme suggested, the magnetic coupling is mediated by a magnetic particle that is in contact with both nanomagnets via tunnel barriers. The time-dependent electric field is applied so that the height of first one barrier then the other is suppressed in an alternating fashion. We show that the result is a pumping of magnetization from one nanomagnet to the other through the mediating particle. The dynamics of the magnetization of the mediating particle allows the coupling to be switched between being ferromagnetic and being antiferromagnetic.     

Single-electron transport in electrically tunable nanomagnets

We study a single-electron transistor (SET) based upon a II-VI semiconductor quantum dot doped with a single-Mn ion. We present evidence that this system behaves like a quantum nanomagnet whose total spin and magnetic anisotropy depend dramatically both on the number of carriers and their orbital nature. Thereby, the magnetic properties of the nanomagnet can be controlled electrically. Conversely, the electrical properties of this SET depend on the quantum state of the Mn spin, giving rise to spin-dependent charging energies and hysteresis in the Coulomb blockade oscillations of the linear conductance.     

Molecular nanomagnets as quantum simulators

Quantum simulators are controllable systems that can be used to simulate other quantum systems. Here we focus on the dynamics of a chain of molecular qubits with interposed antiferromagnetic dimers. We theoretically show that its dynamics can be controlled by means of uniform magnetic pulses and used to mimic the evolution of other quantum systems, including fermionic ones. We propose two proof-of-principle experiments based on the simulation of the Ising model in a transverse field and of the quantum tunneling of the magnetization in a spin-1 system.     

Neutron spectroscopy of molecular nanomagnets

This short overview gives an account on the use of neutron spectroscopy for the examination of molecular nanomagnets, systems constructed by crystalline arrangement of finite size clusters (usually with regular form) of interacting moment carrying atoms ?C magnetic molecules. Opposed to extended magnetic systems with bands of collective excitations such as spin-waves the molecular nanomagnets are entities with local properties, each magnetic molecule possessing a finite number of energy levels that can be solved exactly for small enough systems. In essence, the number of states remains finite despite growing rapidly with increasing number of magnetic centers and the value of the spin quantum number. Increasingly large numbers of states and more complex exchange networks lead to the need for approximative treatments, the validity of which can be checked with neutron spectroscopy. Molecular nanomagnets provide interesting examples of physics and magnetochemistry, illustrated here with a few examples that highlight the power of neutron spectroscopy for precise investigation of the energy level structure and spatial configuration of the magnetic exchange parameters.     

Guided modes below the bulk plasma frequency

We present the results of calculations for a waveguide in which the dielectric constant ? decreases exponentially from a positive value at the surface to a negative value in the bulk, the guided waves propagating perpendicular to ▽?. Both TM and TE modes are found, each having some unusual properties as compared with modes in the same guides above the plasma frequency. These modes could be realized at 10.6 μm in suitably doped GaAs.     

Fundamental frequency patterns of Chinesein different speech modes

I.IntroductionTheF,patternsofspeechareimportantnotonlyforthcprosodicfeaturesbuta1soforvoicesourcecharactcristics.Nowmoreandmorespeechscientistsrecognizedthatvoiceexcitationsourceintcxt-to-spccchsystemsp1aysanimportantro1elnbothintclligibilityandnaturalnessorsynthcticspcech.Espccially,forChinese,atone1anguagewithmulti-tonesystem,thetonalpatternswhicharcmainlydcmonstratedintheF,con-tourscarry1exicalmeaning.SomecomparativestudiesoftheF,pattcrnsinbetweentonelanguage(Chinese)andstress1anguage(En…     

Low frequency longitudinal lattice modes in graphite intercalation compounds

Results of inelastic neutron scattering experiments on a stage 2 graphite-FeCl₃ intercalation compound are reported. A one-dimensional Born-von Kármán model is formulated and applied to interpret the data. The application of this model to other recently reported neutron data for donor compounds suggests systematic trends in the magnitudes of the interactions, dependent on the intercalate sandwich thickness.     

Switching frequency for transverse modes in stripe-geometry injection lasers

An expression is obtained for the frequency of a class of oscillations occurring between mirror-image near field distributions in stripe-geometry injection lasers. Computation of the oscillation frequency indicates that values in the GHz range can occur. A means of exploiting this high speed switching is briefly indicated.     

Dephasing of quantum tunnelling in molecular nanomagnets

Dephasing mechanism of quantum tunnelling in molecular magnets has been studied by means of the spin-coherentstate path integral in a mean field approximation. It is found that the fluctuating uncompensated transverse field from the dipolar-dipolar interaction between molecular magnets contributes a random phase to the quantum interference phase. The resulting transition rate is determined by the average tunnel splitting over the random phase. Such a dephasing process leads to the suppression of quenching due to the quantum phase interference, and to the steps due to odd resonances in hysteresis loop survived, which is in good agreement with experimental observations in molecular nanomagnets Fes and Mn12.     

Spin-transfer-driven ferromagnetic resonance of individual nanomagnets

We demonstrate a technique that enables ferromagnetic resonance measurements of the normal modes for magnetic excitations in individual nanoscale ferromagnets, smaller in volume by more than a factor of 50 compared to individual ferromagnetic samples measured by other resonance techniques. Studies of the resonance frequencies, amplitudes, linewidths, and line shapes as a function of microwave power, dc current, and magnetic field provide detailed new information about the exchange, damping, and spin-transfer torques that govern the dynamics in magnetic nanostructures.     

Superradiance from crystals of molecular nanomagnets

We show that crystals of molecular nanomagnets can exhibit giant magnetic relaxation due to the Dicke superradiance of electromagnetic waves. Rigorous theory is presented that combines superradiance with the Landau-Zener effect.     

Phonon superradiance and phonon laser effect in nanomagnets

We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.     

Zero frequency modes of low temperature magnetic phases in YbIG

The stability of low temperature magnetic phases of YbIG in dependence on field and temperature is investigated using the model with six Yb sublattices and one saturated Fe sublattice. The conditions for existence of zero-frequency modes are deduced in the analytical form for magnetic fields lying in {110} planes. General results are applied to the case of magnetic field parallel to [111] direction and the existence of a metastability region is shown, where both the colinear as well as the canted phase may occur.