Presence Of Large Magnetic Field Research Articles

Designing ITER motional Stark effect line shift (MSE-LS) spectrometers.

As a part of ITER beam aided diagnostics, the design of Motional Stark Effect (MSE) diagnostic observing the emission from the Balmer-α line is underway. The physics of Stark splitting shows that the Stark manifold is polarization dependent, and the energy splitting results in a line shift proportional to the electric field. Due to the challenges of maintaining the calibration of the plasma facing mirrors in ITER, the conventional MSE polarimetry measurement technique is replaced with a spectral approach that is deemed more favorable in the ITER environment. The MSE line shift (LS) diagnostic is designed to quantify the Lorentz electric field magnitude by measuring the Stark manifold using visible spectroscopy. In the presence of large magnetic fields and high energy heating beams of 1MeV, the expected Stark splitting is much larger than in typical devices. The MSE-LS design has unique challenges requiring careful consideration and modeling of its viewing geometry and photon budget. The MSE-LS approach on ITER is promising but has stringent demands on the allowable errors for the statistical and systematic fitting uncertainties. In this study, a full system model and numerical simulations of data for each sightline are completed. For a range of optical transmission fractions, photon noise analysis is conducted to determine the statistical uncertainties. This provides guidance on the spectrometer throughput, dispersion at the detector, optics, and other design choices. A conceptual design of a high throughput spectrometer with a volume phase transmission grating is presented.

Calculation of dipole matrix elements for the modeling of H-[formula omitted] Stark broadening in the presence of large magnetic field

B-spline basis sets are applied to the calculation of dipole matrix elements for the hydrogen atom placed in an intense magnetic field, in view of applications to the spectroscopic analysis of white dwarf atmospheres. A focus is put on the H-α line and magnetic field values in the kilotesla range are considered. The dipole matrix elements are shown to be significantly sensitive to the magnetic field. In the framework of plasma diagnostic, this means that the Stark broadening of the line, which is involved in density measurements, can be misinterpreted if the atomic structure is not well accounted for in numerical codes. As an illustration, we consider the H-ασ− component and apply a computer simulation method to the modeling of the Stark broadening of this line. The calculated dipole matrix elements are used therein as input.

Thermal properties of the core of magnetar

During very early age of neutron stars, the core cools down faster compared to the crust creating a large thermal gradient in the interior of the star. During 10−100 years, a cooling wave propagates from the core to the crust causing the interior of the star to thermalize. During this duration thermal properties of the core material is of great importance to understand the dynamics of the interior of the star. The heat capacity and thermal conductivity of the core depends on the behaviour of matter inside the core. We investigate these two properties in case of magnetars. Due to presence of large magnetic field, the proton superconductivity is quenched partially inside the magnetars depending upon the comparative values of upper critical field and the strength of the magnetic field present. This produces non-uniformity in the behaviour of matter throughout the star. Moreover, such non-uniformity arises from the variation of nature of the pairing and values of the pairing gap energy. We find that the heat capacity is substantially reduced due to the presence of superfluidity. On the other hand, the thermal conductivity of neutron is enhanced due to proton superconductivity and gets reduced due to neutron superfluidity. Hence, the variation of the thermal properties due to superfluidity in presence of magnetic field is different at different radius inside the star. However, in all the cases the maximum variation is of the order one. This affects the thermal relaxation time of the star and eventually its the thermal evolution.

Comment on “Thermal properties of magnons in yttrium iron garnet at elevated magnetic fields”

Rezende and L\'opez Ortiz [Phys. Rev. B 91, 104416 (2015)] published a calculation for the magnon specific heat and thermal conductivity of yttrium iron garnet in the presence of large magnetic fields. The results reproduced our previous temperature-dependent measurements of both quantities in fields up to 70 kOe [Phys. Rev. B 90, 064421 (2014)]. Here, we point out that the experimentally observed magnetic-field dependence of thermal conductivity shows a faster saturation than their model explains. Furthermore, their results do not affect the main conclusion of our paper regarding the magnon thermal mean-free path.

The Quantum Spin Hall Effect

Most quantum states of condensed matter are classified by the symmetries they break. For example, crystalline solids break translational symmetry, and ferromagnets break rotational symmetry. By contrast, topological states of matter evade traditional symmetry-breaking classification schemes, and they signal the existence of a fundamentally different organizational principle of quantum matter. The integer and fractional quantum Hall effects were the first topological states to be discovered in the 1980s, but they exist only in the presence of large magnetic fields. The search for topological states of matter that do not require magnetic fields for their observation led to the theoretical prediction in 2006 and experimental observation in 2007 of the so-called quantum spin Hall effect in HgTe quantum wells, a new topological state of quantum matter. In this article, we review the theoretical foundations and experimental discovery of the quantum spin Hall effect.

Observation of the fractional quantum Hall effect in graphene

When electrons are confined in two dimensions and subject to strong magnetic fields, the Coulomb interactions between them can become very strong, leading to the formation of correlated states of matter, such as the fractional quantum Hall liquid. In this strong quantum regime, electrons and magnetic flux quanta bind to form complex composite quasiparticles with fractional electronic charge; these are manifest in transport measurements of the Hall conductivity as rational fractions of the elementary conductance quantum. The experimental discovery of an anomalous integer quantum Hall effect in graphene has enabled the study of a correlated two-dimensional electronic system, in which the interacting electrons behave like massless chiral fermions. However, owing to the prevailing disorder, graphene has so far exhibited only weak signatures of correlated electron phenomena, despite intense experimental and theoretical efforts. Here we report the observation of the fractional quantum Hall effect in ultraclean, suspended graphene. In addition, we show that at low carrier density graphene becomes an insulator with a magnetic-field-tunable energy gap. These newly discovered quantum states offer the opportunity to study correlated Dirac fermions in graphene in the presence of large magnetic fields.

Are magnetic hot stars intrinsic X-ray sources?

Context. X-ray surveys carried out with the Einstein and ROSAT satellites have resulted in rather unexpected detections of X-ray emission from late B-type and early A-type stars. These stars possess neither winds like early-type stars nor convective envelopes as late-type stars, so that the origin and production mechanism of this X-emission is unclear. Aims. We investigate whether the presence of large magnetic fields is related to the observed X-ray emission. Methods. We carried out Chandra high-angular resolution observations of a sample of late B-type and A-type stars with measured magnetic fields in the range from 0.2-17 kG. Out of the selected 10 sample stars, 6 objects had been previously detected as X-ray sources, some of them, however, with high positional uncertainty and a low signal-to-noise ratio, while 4 of our sample stars do have large magnetic fields but no previous detections of X-ray emission. Results. Our Chandra data confirm all previous ROSAT detections with an extremely high significance, and the limits of the offsets between X-ray and optical positions are greatly improved. In particular, HD 215441, known as Babcock's star with the strongest magnetic field by far (17 kG) of our sample stars, a rather faint and somewhat marginal ROSAT source, can clearly be detected. However, none of the 4 ROSAT non-detections could be detected with the new Chandra observations. Conclusions. The pure existence of a magnetic field of kiloGauss strength on a late B-type or A-type star is therefore not necessarily a prerequisite for finding X-ray emission among these stars. Understanding the observed X-ray emission from Babcock's star is a challenge for observational and theoretical astrophysics.

Understanding the current-induced magnetization dynamics in the presence of large magnetic fields

We have theoretically studied the magnetization behavior in the magnetic trilayer nanostructures under the influence of spin-transfer torque using the Landau–Lifshitz–Gilbert equation. The focus is the coherent transition of the magnetization from a static state to another static state induced by the spin current even in the presence of a large applied field. Based on the study, the experimental observations, which were thought to be due to spin-wave excitations previously, can be directly and quantitatively explained by the out-of-plane static states of the magnetization induced by the spin-current in the presence of large in-plane magnetic fields in the range of several Teslas.

Nonmagnetic piston–cylinder pressure cell for use at 35 kbar and above

A piston–cylinder cell has been constructed which makes it possible to achieve pressures of over 35 kbar at room temperature, and more than 29 kbar in a cryogenic environment. The use of a nonmagnetic cobalt–nickel alloy with an unusually high yield strength (1.97 GPa at 293 K) allows the cell to be used in the presence of large magnetic fields. It seems likely that the cobalt–nickel material can be used as a direct replacement for the celebrated (but largely unavailable) Russian nickel alloy in many applications where nonmagnetic pressure cells are needed. Such applications may also include other kinds of high pressure apparatus, such as diamond anvil and sapphire anvil cells. The pressure cell described in the present article employs the “Teflon cap” technique, and detailed information concerning the application of this method is given which can be used with a wide variety of cells of the piston–cylinder type.

Comment on “Observation of vortex-lattice melting inYBa2Cu3O7−δby Seebeck-effect measurements”

The findings of Ghamlouch et al. [Phys. Rev. B 54, 9070 (1996)] on the jump in the thermoelectric power of high-${T}_{c}$ superconductors below the critical temperature in the presence of large magnetic fields are discussed. The complicated interplay between the vortex lattice thermodynamic transitions and the transport property percolation transitions raises questions on their similarities, differences, and relationships with respect to the (B,T) phase diagram features and the classical Kosterlitz-Thouless transition. A few comments pertain to the experimental details and others on the relevant role of thermomagnetic transport properties.

EFFECT OF STRONG MAGNETIC FIELDS ON THE EQUILIBRIUM OF A DEGENERATE GAS OF NUCLEONS AND ELECTRONS

We obtain the equations that define the equilibrium of a homogeneous relativistic gas of neutrons, protons and electrons in a constant magnetic field as applied to the conditions that probably occur near the center of neutron stars. We compute the relative densities of the particles at equilibrium and the Fermi momentum of electrons in the strong magnetic field as function of the density of neutrons and the magnetic field induction. Novel features are revealed as to the ratio of the number of protons to the number of neutrons at equilibrium in the presence of large magnetic fields.

Paramagnetism and reentrant behavior in quasi-one-dimensional superconductors at high magnetic fields

The thermodynamics of quasi-one-dimensional superconductors in the presence of large magnetic fields is studied. When the quantum effects of the magnetic field are taken into account, several reentrant superconducting phases persist at very high fields. In the last reentrant phase the free-energy change, the specific-heat jump and the excess magnetization are estimated near the critical temperature. In particular, the excess magnetization is found to be paramagnetic as opposed to diamagnetic in weak fields and its sign is controlled by the slope of H c2( T). We further generalize this result to the entire phase diagram (including all quantum phases) and to different physical systems using general thermodynamic relations which show that the sign of the excess magnetization ΔM of the superconducting state near H c2( T) follows dH c2 (T) dT . These relations provide a scenario for the evolution of the sign of ΔM from weak fields to strong fields.

In situ Mössbauer spectroscopy of carbon-supported iron catalysts at cryogenic temperatures and in external magnetic fields

A highly dispersed carbon-supported iron catalyst has been studied within situ Mossbauer spectroscopy at temperatures down to 5 K and with external magnetic fields. It is shown that measurements of spectra in the presence of large magnetic fields considerably improves the information obtained from Mossbauer spectra.

Effects of localized phonon modes on magnetotunneling spectra in double-barrier structures.

The effects of localized phonon modes on the low-temperature current-voltage curves of GaAs/AlAs double-barrier resonant-tunneling structures have been calculated in the presence of large magnetic fields parallel to the applied electric field. The applied magnetic field sharpens and increases the height of the phonon-assisted-tunneling peaks in agreement with experimental data. Computed magnetotunneling spectra reveal systematic deviations from a simple fan structure---also observed experimentally---which are attributed here to oscillations of the emitter Fermi level with the magnetic field.

酸化物超電導体の高Ｊｃ化

One of the most important properties for application of superconductors is critical current density(Jc). Jc of order 105 to 106A/cm2 is required often in the presence of large magnetic fields. However, Jc values of oxide superconductors remained low except thin films. It is also pointed out that large dissipation or flux creep becomes a serious problem for applications at higher temperatures. In fact, large flux creep is observed in thin films despite high Jc.In order to achieve high Jc values, we need to introduce effective pinning centers which can prevent the motion of flux against the Lorentz force (FL=JxB). In this paper, I first summarize how Jc is determined in type II superconductors. Then I present the methods to increase Jc values in oxide superconductors and show that the flux creep rate becomes small when the pinning force or Jc is increased. Finally I propose some possible applications for high Jc bulk oxide superconductors.

Doppler Images of Rapidly Rotating Ap Stars

The magnetic Ap stars are characterized by the presence of large magnetic fields which undergo periodic variations. These magnetic field variations are accompanied by spectral variations caused by the inhomogeneous distribution of elements on the stellar surface. It is believed that the magnetic field plays an important role in determining this distribution. Accurate maps of the surface distribution of elements would provide valuable probes as to the field geometry as well as provide clues to the role of the magnetic fields in the atmospheres of these stars. We have developed a new technique for mapping the local equivalent width on a stellar surface from the observed spectral line variations.

The superfluid phase transition in pulsars

Renormalisation group equations are derived from the Ginzburg-Landau free energy for p-wave paired neutron-star matter in the presence of large magnetic fields. The effect of fluctuations on the nature of the superfluid phase transition is discussed.

The Quadratic Zeeman Effect for CI Lines-Application to the Spectrum of EG 129

Garstang and Kemic (1974) derived formulae for the splitting of hydrogen and helium lines in the presence of large magnetic fields. We applied their method in calculating the eigenvectors for some transitions of neutral carbon, where a correction factor for the coupling and mixing of the energy levels has to be applied. For CI – lines in the visible region of the spectrum, well separated components can be expected for a field strength up to 2 • 107G. Fig. 1 shows the splitting of three lines for B = 107 G.

Possible "New" Quantum Systems

Systems of spin-aligned hydrogen isotopes are studied. They are shown to exhibit even more extreme "quantum" behavior than the helium isotopes. Spin-aligned hydrogen is predicted to be a gas at all temperatures and its Bose-Einstein condensation and possible superfluidity are discussed. Spin-aligned deuterium is predicted to show critical behavior strongly influenced by quantum mechanics. The preparation of spin-aligned hydrogen (in the presence of large magnetic fields) is also discussed.

Neutrino synchrotron radiation

The neutrino synchrotron radiation for a completely relativistic electron gas in the presence of large magnetic field is computed according to the photon neutrino coupling theory of weak interactions. The radiation is also estimated for the non-relativistic case. The neutrino luminosity of several model white dwarfs are computed according to the photon-neutrino coupling theory and compared with that of the current-current coupling theory. It is shown that, according to the photonneutrino coupling theory, the neutrino luminosity is greater than the photon luminosity and, therefore, most likely to have astrophysical significance in the evolution of stars with large electron energies and potentially large magnetic field, such as white dwarfs.