Tilted Magnetic Field Research Articles

The inner heliospheric source for keV-energetic IBEX ENAs

Context. Up to now, three succesive full-sky maps of heliospheric fluxes of KeV-energetic neutral H-atoms have been registered with the satellite IBEX. The most outstanding feature persisting in these maps is the so-called ribbon which appears as an arc around the upwind direction with unexpectedly high fluxes. This radiation feature was not predicted by models, but at present is tentatively explained as due to energetic plasma sites outside the heliosphere in regions beyond the heliopause. Aims. Since all these proposed explanations, however, need to rely on unproven energizing ion processes, we shall investigate in this article alternative ion sources of keV-ENAs that in contrast appear much closer to the sun, but are based on a clear concept of ion energization to KeV energies, namely suprathermal pick-up ions at a few AU inside and outside of the solar wind termination shock. Methods. Using well-established models for the solar wind magnetic field and the heliospheric TS surface, we derive skymaps of the magnetic field tilt angle, the resulting injection efficiency and the resulting ENA flows. The results are normalised to the ion flux observations made by Voyager-1. We also discuss basic modifications of the TS geometry within the framework of the model. Results. We calculate ENA fluxes of these pick-up ions and show that they, due to their sensitivities to magnetic tilt angles at the termination shock surface, reveal a radiative sickle feature around the upwind direction which in many of its properties resembles the ENA ribbon feature seen by IBEX, although the highest IBEX intensities do not seem to be quantitatively representable by our calculations.

Modeling the radio signature of the orbital parameters, rotation, and magnetic field of exoplanets

Context. Since the first extra-solar planet discovery in 1995, several hundreds of these planets have been discovered. Most are hot Jupiters, i.e. massive planets orbiting close to their star. These planets may be powerful radio emitters.Aims. We simulate the radio dynamic spectra resulting from various interaction models between an exoplanet and its parent star, i.e. exoplanet-induced stellar emission and three variants of the exoplanet’s magnetospheric auroral radio emission (full auroral oval, active sector fixed in longitude, and active sector fixed in local time).Methods. We show the physical information about the system that can be drawn from radio observations, and how this can be achieved. This information includes the magnetic field strength and the rotation period of the emitting body (planet or star), the orbital period, the orbit’s inclination, and the magnetic field tilt relative to the rotation axis or offset relative to the center of the planet. For most of these parameters, radio observations provide a unique means of measuring them.Results. Our results should provide the proper framework of analysis and interpretation for future detections of radio emissions from exoplanetary systems – or from magnetic white dwarf-planet or white dwarf-brown dwarf systems –, that are expected to commence soon as part of extensive programs at large radiotelescopes such as LOFAR, UTR2 or the GMRT. Our methodology can be easily adapted to simulate specific observations, once effective detection is achieved.

A probability assessment of encountering dayside magnetopause diffusion regions

[1] Probability maps for encountering the reconnection electron diffusion region of the dayside magnetopause have been developed using a model of reconnection and solar wind observations. The maps indicate that along the magnetopause surface, the chance of directly sampling the diffusion region during a given season varies considerably. The probability distribution depends strongly on the distribution of interplanetary magnetic field directions and, also, is significantly influenced by the Earth's intrinsic magnetic dipole field tilt angle. The probability also scales with the assumed size of the diffusion region. The probability distribution shows little dependence on the phase of the solar cycle.

Modeling the young Sun's solar wind and its interaction with Earth's paleomagnetosphere

We present a focused parameter study of solar wind - magnetosphere interaction for the young Sun and Earth, $~3.5$ Ga ago, that relies on magnetohydrodynamic (MHD) simulations for both the solar wind and the magnetosphere. By simulating the quiescent young Sun and its wind we are able to propagate the MHD simulations up to Earth's magnetosphere and obtain a physically realistic solar forcing of it. We assess how sensitive the young solar wind is to changes in the coronal base density, sunspot placement and magnetic field strength, dipole magnetic field strength and the Sun's rotation period. From this analysis we obtain a range of plausible solar wind conditions the paleomagnetosphere may have been subject to. Scaling relationships from the literature suggest that a young Sun would have had a mass flux different from the present Sun. We evaluate how the mass flux changes with the aforementioned factors and determine the importance of this and several other key solar and magnetospheric variables with respect to their impact on the paleomagnetosphere. We vary the solar wind speed, density, interplanetary magnetic field strength and orientation as well as Earth's dipole magnetic field strength and tilt in a number of steady-state scenarios that are representative of young Sun-Earth interaction. This study is done as a first step of a more comprehensive effort towards understanding the implications of Sun-Earth interaction for planetary atmospheric evolution.

Anisotropy of Magnetoresistance Hysteresis around the ν=2/3 Quantum Hall State in Tilted Magnetic Field

We present an anisotropy of the hysteretic transport around the spin transition point at Landau level filling factor $\nu=2/3$ in tilted magnetic field. When the direction of the in-plane component of the magnetic field $B_{\parallel}$ is normal to the probe current $I$, a strong hysteretic transport due to the current-induced nuclear spin polarization occurs. When $B_{\parallel}$ is parallel to $I$, on the other hand, the hysteresis almost disappears. We also demonstrate that the nuclear spin-lattice relaxation rate $T_{1}^{-1}$ at the transition point increases with decreasing angle between the directions of $B_{\parallel}$ and $I$. These results suggest that the morphology of electron spin domains around $\nu =2/3$ is affected by the current direction.

Angular Dependence of Optically Detected Magnetophonon Resonances in Miniband Transport in Semiconductor Superlattice under Tilted Magnetic Fields

The angular dependence of the optically detected magnetophonon resonance (ODMPR) for the frequency-dependent magnetoconductivity in a Ge-based (nonpolar) semiconductor superlattice under a tilted magnetic field is investigated. The frequency-dependent magnetoconductivity, including the miniband width, the periodic potential, the photon frequency, and the tilt angle of a magnetic field tilted relative to the superlattice axis, is calculated using the nonpolar LO phonon modes as a function of the magnetic field strengths. In particular, the angular dependence of the ODMPR lineshape, such as the splitting and the shift of the ODMPR peaks for the photon frequency, is discussed. Furthermore, the angular dependences for the appearance of the plateau region between two neighboring ODMPR peaks and the change in the ODMPR amplitude as a function of the tilt angle of the tilted magnetic field for various miniband widths and photon frequencies are discussed in detail.

Dynamic nuclear polarization and nuclear magnetic resonance in the simplest pseudospin quantum Hall ferromagnet

We present dynamic nuclear polarization (DNP) in the simplest pseudospin quantum Hall ferromagnet (QHF) of an InSb two-dimensional electron gas with a large g factor using tilted magnetic fields. The DNP-induced amplitude change of a resistance spike of the QHF at large current enables observation of the resistively detected nuclear magnetic resonance of the high nuclear spin isotope 115In with nine quadrupole splittings. Our results demonstrate the importance of domain structures in the DNP process. The nuclear spin relaxation time T1 in this QHF was relatively short (~ 120 s), and almost temperature independent.

Ionospheric convection signatures of the interchange cycle at small interplanetary magnetic field clock angles

The purpose of this paper is to show a “proof of the existence” of the ionospheric situation that is expected for the interchange cycle, during periods of favorable interplanetary magnetic field (IMF) and dipole tilt conditions. To do so, we present three case studies of dayside high‐latitude ionospheric convection that is observed around the equinoxes (near‐zero dipole tilt) and at small IMF clock angles (one θc ∼ −30° event and two θc ∼ 30° events, where θc ≡ Arg(BZ + iBY)), using Super Dual Auroral Radar Network (SuperDARN)/Defense Meteorological Satellite Program (DMSP)/National Oceanic and Atmospheric Administration (NOAA) data in the Northern Hemisphere and, when available, DMSP data in the Southern Hemisphere. The convection pattern exhibits twin reverse cells in both hemispheres, but the constituents of each cell are different. In the Northern Hemisphere, for θc ∼ 30° (θc ∼ −30°), the center of the dawnside (duskside) cell is located poleward of the polar cap boundary, while the center of the duskside (dawnside) cell is located equatorward of the polar cap boundary. For θc ∼ 30°, we confirmed that the above‐mentioned dawn‐dusk relation reverses in the Southern Hemisphere. The north‐south asymmetric behavior of the conjugate reverse cells, on the dawnside and duskside each, is consistent with two independent interchange cycles that result from the coupling of IMF‐lobe reconnection in one hemisphere with lobe‐closed reconnection in the opposite hemisphere.

Locking and unlocking of the counterflow transport inν=1quantum Hall bilayers by tilting of magnetic field

The counterflow transport in quantum Hall bilayers provided by superfluid excitons is locked at small input currents due to a complete leakage caused by the interlayer tunneling. We show that the counterflow critical current I_c^{CF} above which the system unlocks for the counterflow transport can be controlled by a tilt of magnetic field in the plane perpendicular to the current direction. The effect is asymmetric with respect to the tilting angle. The unlocking is accompanied by switching of the systems from the d.c. to the a.c. Josephson state. Similar switching takes place for the tunneling set-up when the current flowing through the system exceeds the critical value I_c^T. At zero tilt the relation between the tunnel and counterflow critical currents is I_c^T=2 I_c^{CF}. We compare the influence of the in-plane magnetic field component B_\parallel on the critical currents I_c^{CF} and I_c^T. The in-plane magnetic field reduces the tunnel critical current and this reduction is symmetric with respect to the tilting angle. It is shown that the difference between I_c^{CF} and I_c^T is essential at field |B_\parallel|\lesssim \phi_0/d \lambda_J, where \phi_0 is the flux quantum, d is the interlayer distance, and \lambda_J is the Josephson length. At larger B_\parallel the critical currents I_c^{CF} and I_c^T almost coincide each other.

Phase-space characterization of complexity in quantum many-body dynamics

We propose a phase-space Wigner harmonics entropy measure for many-body quantum dynamical complexity. This measure, which reduces to the well-known measure of complexity in classical systems and which is valid for both pure and mixed states in single-particle and many-body systems, takes into account the combined role of chaos and entanglement in the realm of quantum mechanics. The effectiveness of the measure is illustrated in the example of the Ising chain in a homogeneous tilted magnetic field. We provide numerical evidence that the multipartite entanglement generation leads to a linear increase in entropy until saturation in both integrable and chaotic regimes, so that in both cases the number of harmonics of the Wigner function grows exponentially with time. The entropy growth rate can be used to detect quantum phase transitions. The proposed entropy measure can also distinguish between integrable and chaotic many-body dynamics by means of the size of long-term fluctuations which become smaller when quantum chaos sets in.

Magnetoresistivity and acoustoelectronic effects in a tilted magnetic field in p-Si/SiGe/Si structures with an anisotropic g factor

Magnetoresistivity $\rho _{xx}$ and $\rho _{xy}$ and the acoustoelectronic effects are measured in $p$-Si/SiGe/Si with an impurity concentration $p$ = 2 $\times $ 10$^{11}$ cm$^{-2}$ in the temperature range 0.3-2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective $g$-factor on the angle of magnetic field tilt $\theta $ to the normal to the plane of a two dimensional $p$-Si/SiGe/Si channel is determined. A first order ferromagnet-paramagnet phase transition is observed in the magnetic fields corresponding to a filling factor $\nu $ = 2 at $\theta \approx $ 59$^\textrm{o}$-60$^\textrm{o}$.

Anisotropy of the Upper Critical Field in a TiltedMagnetic Field for Sr2RuO4

Anisotropy of the Upper Critical Field in a TiltedMagnetic Field for Sr2RuO4

G-Factor of low mobility 2D GaAs electron gas as determined from high magnetic field experiments

We study low-mobility 2D electron gas in GaAs quantum well in tilted magnetic field up to 45 T. Analyzing the behavior of the Shubnikov-de Haas (SdH) oscillations we obtain the value of g-factor, | g | = 0.9 ± 0.1 , which is noticeably larger than that predicted theoretically and obtained from optical experiments. Possible reasons of the discrepancy are discussed.

Mechanism of the photoelectromagnetic effect in two-dimensional systems in quantizing magnetic fields

A new mechanism of the photovoltaic effect in a terahertz frequency range is proposed that is capable of explaining the features of terahertz photocurrents observed previously in asymmetric InAs quantum wells and double GaAs quantum wells in an external tilted magnetic field. It is shown that, in the asymmetric semiconductor heterostructures occurring in a tilted magnetic field, an edge photocurrent is generated due to the absorption of radiation on the electron transitions between Landau levels. A new approach to the creation of highly sensitive terahertz photodetectors based on asymmetric semiconductor heterostructures is proposed.

SPIN RESOLVED SUBBAND-LANDAU-LEVEL COUPLING AND ELECTRON-HOLE COUPLING IN InAs/AlGaSbAs QUANTUM WELL

We have investigated the magneto-transport properties in InAs / AlGaSbAs quantum well (QW), where the lattice mismatch is less than 0.5%. In tilted magnetic fields, the spin-resolved subband-Landau-level coupling has been clearly observed in the magneto-resistance due to the large g -factor of this QW. An anomaly in the Hall effect has been observed at high magnetic fields of the filling factor being less than unity, which is caused by the coexistence of electrons and holes in the system.

Equilibrium of Nonneutral Plasmas in a Malmberg-Penning Trap with a Tilted Magnetic Field

The effect of a weakly tilted magnetic field perturbations on the equilibrium of a nonneutral plasma confined in a Malmberg-Penning trap is analyzed. A constraint is introduced, that in combination with the Poisson equation allows to select admissible plasma equilibria in the trap in the presence of a non-uniform and a non-axisymmetric magnetic field. Longitudinal plasma currents (analogous to the Pfirsch-Schlüter currents in Tokamaks) appearing in a nonneutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field.

Evolution of the spin-split quantum Hall states with magnetic field tilt in the InAs-based double quantum wells

Development of quantum Hall peculiarities due to mobility gap between spin-split magnetic levels with addition of the parallel magnetic field component B|| is analyzed in double quantum wells (DQW) created in InGaAs/GaAs and InAs/AlSb heterosystems chosen due to their relatively large bulk g-factors. In InGaAs/GaAs DQWs, the nonmonotonous behavior of these peculiarities is observed and explained within single-electron approach in terms of competition between enhanced spin splitting and localization of electrons in the layers of DQW with increased B||. In InAs/AlSb DQW, the tunneling connection between the layers is very weak due to high barrier, nevertheless the collective odd-numbered peculiarities are revealed that exist due to spontaneous interlayer phase coherence. B|| destroys these states that is manifested, in particular, in the suppression of the peculiarity for filling factor v = 3.

Analytic model of near-field radio-frequency sheaths. I. Tenuous plasma limit

An analytic model is derived for electromagnetic radio-frequency (rf) wave propagation in a waveguide filled by a tenuous plasma with a slightly tilted equilibrium magnetic field B, i.e., by=By/B⪡1. The calculation includes the self-consistent coupling between the rf fields and the sheaths at the sheath-plasma interface and can be used to describe antenna sheath formation in the ion cyclotron range of frequencies. The sheaths are treated as thin vacuum regions separating the plasma and metal wall. It is shown that (i) the launched fast wave is coupled parasitically to the slow wave by the magnetic field structure when by≠0 and by the sheath boundary condition, (ii) the sheath voltage Vsh is dependent on the wave parity (the “antenna phasing”), and (iii) integrating the vacuum rf fields, Vvac=−∫dzE∥(vac), gives an overestimate of the sheath voltage. An expression for the self-consistent Vsh including plasma effects and satisfying the Child–Langmuir law is obtained.

Admissible Equilibria of Non-neutral Plasmas in a Malmberg-Penning Trap

A "parallel current constraint" is derived, that in combination with the Poisson equation allows one to select admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap in the presence of a nonuniform and nonaxisymmetric magnetic field. Asymmetry-induced currents (analogous to the Pfirsch-Schlüter currents in Tokamaks) appearing in a non-neutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field.

INFORMATION GEOMETRY, INFERENCE METHODS AND CHAOTIC ENERGY LEVELS STATISTICS

In this letter, we propose a novel information-geometric characterization of chaotic (integrable) energy level statistics of a quantum antiferromagnetic Ising spin chain in a tilted (transverse) external magnetic field. Finally, we conjecture our results might find some potential physical applications in quantum energy level statistics.