Large Transverse Magnetic Field Research Articles

Solitonic excitations in the Ising anisotropic chain BaCo2V2O8 under large transverse magnetic field

We study the dynamics of the quasi-one-dimensional Ising-Heisenberg antiferromagnet ${\mathrm{BaCo}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ under a transverse magnetic field. Combining inelastic neutron scattering experiments and theoretical analyses by field theories and numerical simulations, we mainly elucidate the structure of the spin excitation spectrum in the high-field phase, appearing above the quantum phase transition point ${\ensuremath{\mu}}_{0}{H}_{c}\ensuremath{\approx}10\phantom{\rule{0.28em}{0ex}}\mathrm{T}$. We find that it is characterized by collective solitonic excitations superimposed on a continuum. These solitons are strongly bound in pairs due to the effective staggered field induced by the nondiagonal $g$ tensor of the compound and are topologically different from the fractionalized spinons in the weak-field region. The dynamical susceptibility numerically calculated with the infinite time-evolving block decimation method shows an excellent agreement with the measured spectra, which enables us to identify the dispersion branches with elementary excitations. The lowest-energy dispersion has an incommensurate nature and has a local minimum at an irrational wave number due to the applied transverse field.

Uniform Bound of the Entanglement for the Ground State of the Quantum Ising Model with Large Transverse Magnetic Field

We consider the ground state of the quantum Ising model with transverse field $h$ in one dimension in a finite volume \[ \Lambda{_{m}:=\{-m,-m+1,\ldots,m+L\}\ .}% \] For $h$ sufficiently large we prove a bound for the entanglement of the interval $\Lambda_{0}:=\left\{ 0,..,L\right\} $ relative to its complement $\Lambda_{m}\backslash\Lambda_{0}$ which is uniform in $m$ and $L$. The bound is established by means of a suitable cluster expansion.

Experimental determination of phonon thermal conductivity and Lorenz ratio of single crystal metals: Al, Cu, and Zn

We use a magnetothermal resistance method to measure lattice thermal conductivity of pure single crystal metals over the intermediate temperature range of 5–60 K. Large transverse magnetic fields are applied to suppress electronic thermal conduction. The total thermal conductivity and the electrical conductivity are measured as functions of applied magnetic field. The lattice thermal conductivity is then extracted by extrapolating the thermal conductivity versus electrical conductivity curve at zero electrical conductivity. We used this method to experimentally measure the lattice thermal conductivity and Lorenz number in single crystal Al (100), Cu (100), and Zn (001) in the intermediate temperature range. Our results show that the measured phonon thermal conductivity versus temperature plot has a peak around ΘD/10, and the Lorenz number is found to deviate from the Sommerfeld value in the intermediate temperature range.

Large out-of-plane and linear in-plane magnetoresistance in layered hafnium pentatelluride

The prediction of the quantum spin Hall effect in two-dimensional ZrTe5 and HfTe5 monolayers has generated considerable recent interest in these materials. In addition, Dirac points and chiral-anomaly-induced negative longitudinal magnetoresistance (MR) have been observed in ZrTe5. Herein, we study the transport behavior of HfTe5 single crystals in detail and find a large (0.9 x 10(4)%) out-of-plane transverse MR, which is among the highest for layered materials reported thus far. We also encounter a large linear in-plane transverse (magnetic field parallel to c, current parallel to a) MR and discuss its possible origin. The mass anisotropy (gamma = 5.4 at 125 K) obtained by scaling angle-dependent MR data is consistent with the HfTe5 elliptical Fermi surface.

Electromagnetic Evaluation of HTS RF Coils for Nuclear Magnetic Resonance

We propose a Helmholtz-type probe coil that uses a high-temperature superconductor (HTS) for use as 700-MHz nuclear magnetic resonance (NMR) RF coils with a high unloaded quality factor (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ). We analyzed the microwave resonant properties of a one-turn coil set face-to-face. The coils were made of a YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) film deposited on an r-plane sapphire substrate. The film thickness was 300 nm. The resonant frequency was found to split into in-phase (lower frequency) and out-phase (higher frequency) modes. We focused on the self-resonant frequency of the one-turn coil. We simulated the horizontal magnetic field caused by the RF coil. Although the coil could generate a sufficiently large transverse magnetic field in the in-phase mode, such a large field could not be generated in the out-phase mode. Therefore, we decided to use the in-phase mode. We also measured and simulated Qu to confirm that it was large enough for use in the 700-MHz NMR system.

PARTICLE ACCELERATION AND WAVE EXCITATION IN QUASI-PARALLEL HIGH-MACH-NUMBER COLLISIONLESS SHOCKS: PARTICLE-IN-CELL SIMULATION

We herein investigate shock formation and particle acceleration processes for both protons and electrons in a quasi-parallel high-Mach-number collisionless shock through a long-term, large-scale particle-in-cell simulation. We show that both protons and electrons are accelerated in the shock and that these accelerated particles generate large-amplitude Alfv\'{e}nic waves in the upstream region of the shock. After the upstream waves have grown sufficiently, the local structure of the collisionless shock becomes substantially similar to that of a quasi-perpendicular shock due to the large transverse magnetic field of the waves. A fraction of protons are accelerated in the shock with a power-law-like energy distribution. The rate of proton injection to the acceleration process is approximately constant, and in the injection process, the phase-trapping mechanism for the protons by the upstream waves can play an important role. The dominant acceleration process is a Fermi-like process through repeated shock crossings of the protons. This process is a `fast' process in the sense that the time required for most of the accelerated protons to complete one cycle of the acceleration process is much shorter than the diffusion time. A fraction of the electrons is also accelerated by the same mechanism, and have a power-law-like energy distribution. However, the injection does not enter a steady state during the simulation, which may be related to the intermittent activity of the upstream waves. Upstream of the shock, a fraction of the electrons is pre-accelerated before reaching the shock, which may contribute to steady electron injection at a later time.

Slow and stored light pulses in the presence of magnetic fields

We systematically studied slow light (SL) and stored light in the presence of a static magnetic field, either parallel to or transverse to the direction of light propagation. The theoretical calculations are in good agreement with the measured data, and paves the way for determining the information of optical density, coupling Rabi frequency, and ground state population distribution of a system. We also observed an unexpected double-peak profile in the output of SL and the retrieved signal of stored light under a large transverse magnetic field. Our work provides a better understanding in the studies of SL and storage of light.

Progress in the mathematical theory of quantum disordered systems

We review recent progress in the mathematical theory of quantum disordered systems: the Anderson transition, including some joint work with Marchetti, the (quantum and classical) Edwards-Anderson (EA) spin-glass model and return to equilibrium for a class of spin-glass models, which includes the EA model initially in a very large transverse magnetic field.

“Current‐line driven” macropores: which current?

AbstractIn the electrochemical elaboration of porous semiconductors and for a certain class of macropores, the pore direction appears to follow the current lines. However, in the presence of a large transverse magnetic field, the current lines at the semiconductor/electrolyte interface exhibit an abrupt change of direction, the current lines on the semiconductor side being tilted with respect to the surface normal. We show here that the pore direction is also tilted, though to a much lesser extent. On the other hand, tilting the current line direction in the electrolyte does not affect the growth direction significantly. We conclude that the main factor governing the pore growth direction is the current direction in the space charge, which is essentially normal to the envelope of the pore fronts. The reasons for the presence of a small magnetic‐field effect are discussed. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Quantum theory of coherent transverse optical magnetism

Density matrix theory is presented to explain recent experimental observations of intense optically induced magnetism due to a “mixed” type of nonlinearity proportional to the product of the electric- and magnetic-field strengths of light. Two previously unknown quadratic optical effects are predicted--namely, transverse optical magnetization and magnetic charge separation--and quantitative agreement is obtained with experimental results regarding the former of these. The mechanistic origin of a third quadratic nonlinearity, namely, magneto-electric second-harmonic generation, which is familiar on a phenomenological basis in classical nonlinear optics, is also examined. Transverse optical magnetism is shown to enable large permeability changes at optical frequencies accompanied by magnetic dispersion near resonances. This phenomenon provides for all-optical generation of magnetic moments, large transverse magnetic fields, static electric dipoles, and terahertz radiation in (unbiased) transparent homogeneous dielectrics or semiconductors. Intriguing possibilities for applications are considered, including magneto-electric refractive index modification, optical electric power generation, and spin control.

Magnetic Quantum Tunneling in the Single-Molecule Magnet Mn12-Acetate

The symmetry of magnetic quantum tunneling (MQT) in the single molecule magnet Mn2-acetate has been determined by sensitive low-temperature magnetic measurements in the pure quantum tunneling regime and high frequency EPR spectroscopy in the presence of large transverse magnetic fields. The combined data set definitely establishes the transverse anisotropy terms responsible for the low temperature quantum dynamics. MQT is due to a disorder induced locally varying quadratic transverse anisotropy associated with rhombic distortions in the molecular environment (2nd order in the spin-operators). This is superimposed on a 4th order transverse magnetic anisotropy consistent with the global (average) S4 molecule site symmetry. These forms of the transverse anisotropy are incommensurate, leading to a complex interplay between local and global symmetries, the consequences of which are analyzed in detail. The resulting model explains: (1) the observation of a twofold symmetry of MQT as a function of the angle of the transverse magnetic field when a subset of molecules in a single crystal are studied; (2) the non-monotonic dependence of the tunneling probability on the magnitude of the transverse magnetic field, which is ascribed to an interference (Berry phase)effect; and (3) the angular dependence of EPR absorption peaks, including the fine structure in the peaks, among many other phenomena. This work also establishes the magnitude of the 2nd and 4th order transverse anisotropy terms for Mn12-acetate single crystals and the angle between the hard magnetic anisotropy axes of these terms. EPR as a function of the angle of the field with respect to the easy axes (close to the hard-medium plane) confirms that there are discrete tilts of the molecular magnetic easy axis from the global (average) easy axis of a crystal, also associated with solvent disorder. The latter observation provides a very plausible explanation for the lack of MQT selection rules, which has been a puzzle for many years.

Growth striations and impurity concentrations in HMCZ silicon crystals

The effect of a large transverse magnetic field on growth striations and impurity concentrations in Czochralski (CZ) silicon crystals was studied. Silicon crystals of 125 mm in diameter were pulled in [1 0 0] direction from 30 kg melt. A magnetic induction of B=2000 G was used to suppress melt convection. The crystals were not found to be striation-free: periodic striations, spaced about 42 μm, due to 25/−0.3 rpm cw crystal/crucible rotation in asymmetric radial thermal field were observed. Preferential chemical etching of heavily doped samples was used to delineate the growth striations. The crystal growth rate estimated from the periodic striations was about 1.1 mm/min, somewhat lower than the nominal pull-rate of 1.5 mm/min. Due to suppression of melt convection, the interstitial oxygen concentration was low: 7–11 ppma (New ASTM) in lightly boron-doped material, which is about half of what is found in a comparable CZ crystal grown without the magnetic field. At this low level, little or no precipitation of interstitial oxygen was induced by a high–low–high annealing of 1150°C/1 h–650°C/1 h–1000°C/11 h. The substitutional carbon was measured to be all <0.1 ppma.

Quantum coherence in biaxial nanomagnets with a large transverse magnetic field

We study quantum coherence of the biaxial spin system with a large magnetic field along an arbitrary direction in the plane of hard and medium axes. Within the framework of the instanton method we present the analytic formula of the oscillation rate as a function of magnitude and direction of the magnetic field, and discuss its thermal effect. These features are expected to be tested in existing experimental techniques.

Surface polaritons in a GaAs/AlGaAs heterojunction in a high magnetic field

The spectrum of the surface polaritons (SP) in a GaAs/AlGaAs heterojunction in the presence of a large transverse quantizing magnetic field is calculated under the quantum Hall effect conditions. The dispersion properties of the SPs are studied taking into consideration the values of the dielectric constants of the GaAs and the media, and the finite thickness, d, of the layer. It is shown that in the vicinity of the electron cyclotron resonance, the SPs become slow waves, and their group velocity exhibits stepwise behaviour. The magnitude of these steps is determined by the fine-structure constant, , the thickness d of the layer, and the dielectric constants of GaAs and . It is found that the values of the phase and the group velocities of the SPs can significantly decrease with increasing thickness, d, of the layer and with increasing difference between the dielectric constants of GaAs and . Numerical results for the dispersion curves are presented for representative cases. The possibility of experimental observation of the effects considered is discussed.

Extraction-induced emittance growth for negative-ion sources

Nonlinear emittance growth produced by ion extraction is considered by a 3-D analysis in a Vlasov–Poisson–Boltzmann formulation. Phenomena considered include (1) presheath effects, including electron depletion, (2) electron sheath accumulation (for large transverse magnetic fields), (3) nonlinear sheath fields (obtained by a self-consistent solution with an assumed quasiequilibrium positive-ion distribution and at least one Vlasov distribution), (4) nonlinear fringe fields produced by the accelerator-extractor itself [obtained self-consistently with item (3) above], (5) nonlinear space charge of the beam itself, and (6) beam in conjunction with extracted electrons. For specific volume negative-ion source configurations, an investigation of the contribution of aberrations caused by an electron trap and electron accumulation in the extraction sheath are studied. Either of these effects can contribute significantly to the beam emittance, possibly dominating the contribution of the negative-ion temperature in the source.

Collective excitations of edge state electrons in quasi-one-dimensional quantum well wires

Collective excitations of edge state electrons in a quasi-one-dimensional quantum well wire under a large transverse magnetic field at zero temperature are investigated theoretically. The plasmon modes for both intrasubband and intersubband excitations are found at different magnetic field strengths and quasi-1D electron density, in the long wavelength limit. The plasmon dispersion relations, which are all acoustic-like, also show an anisotropy which can be attributed to the applied field and the finite width of the wire. These predictions are amenable to experimental verifications.

Heat Transfer in Rectangular First Wall Coolant Channels of Liquid-Metal-Cooled Blankets

Heat transfer in magnetohydrodynamic flow of a liquid metal in rectangular ducts with thin conducting walls in the presence of a large transverse magnetic field is examined. A significant fraction of the fluid flow, in the form of high velocity jets, is confined within the boundary layers (side layers) adjacent to the side walls which are parallel to the magnetic fields. The existence of the high velocity jets may drastically enhance the cooling capacity. Two schemes - integral and explicit - for the treatment of the flow in the side layers are discussed. Heat transfer calculations based on these schemes are compared.

STARE and GEOS 2 observations of a storm time Pc 5 ULF pulsation

A study is presented of a storm time Pc 5 pulsation, observed by GEOS 2 particle detectors and magnetometers at geocentric orbit and by the STARE auroral radar in the ionosphere. These measurements allow the comparison of phase relationships between the magnetic field components, energetic particle flux, and electric field in the ionosphere over a substantial region. They also permit measurements of the wavelength of the disturbance in the ionosphere. A theory of the coupling between a drift mirror wave and a standing Alfvén wave is developed. The results are compared with this theory and are found to support it. In particular, it is found that the disturbance is of wavelike nature, propagating westward in the equatorial plane at 6.6 RE with a wavelength of about 1 RE. Its period is initially 213 s, lengthening to 300 s later in the event. In the equatorial plane the disturbance in the particle flux and the compressional magnetic field are out of phase as is consistent with a drift mirror wave. There is a large transverse magnetic field oscillation in the meridian plane as is consistent with a guided poloidal oscillation. In the ionosphere the oscillation is consistent with the existence of a guided poloidal Alfvén wave and is entirely different from toroidal oscillations that have been observed at Pc 5 frequencies on other occasions. The observations are consistent with a particle driven drift mirror wave, couplied to a standing Alfvén wave. The azimuthal wavelength is consistent with a drift mirror wave whose Doppler shifted frequency matches the natural frequency of the standing Alfvén wave.

Marangoni convection in a liquid layer under the simultaneous action of a transverse magnetic field and rotation

Asymptotic stability characteristics with respect to the onset of Marangoni convection in a liquid layer under the simultaneous action of a large transverse magnetic field and a large rate of rotation are investigated. In certain parameter ranges there is a decrease in critical Marangoni number for increasing magnetic field and rotation depending on the coupling between interfacial perturbations and rotation.

Parametric excitation of acoustic waves in piezoelectric solid state magnetoplasma

Absolute instability of the acoustic wave (excited parametrically) has been explored on the basis of the Bers and Briggs criterion in the presence of a large transverse static magnetic field. In the magnetoplasma threshold the electric field decreases to about 0.4 times the value at zero magnetic field.