Magnetoresistance of intermediate concentration n-Ge at helium temperatures

1987 ◽  
Vol 65 (1) ◽  
pp. 88-89
Author(s):  
E. El-Rafey ◽  
S. A. El-Atawy
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Conduction Band ◽  
Doping Level ◽  
Intermediate Level ◽  
Transverse Magnetoresistance ◽  
Temperature Range ◽  
Lower Temperature ◽  
Intermediate Concentration ◽  
Partial Compensation

Transverse magnetoresistance (TMR) measurements have been carried out at 4.2 and 1.7 K for magnetic fields up to 25 kG. The sample used is Sb-doped Ge with an intermediate level of concentration, ~6 × 1016 cm−1. At this doping level, two conduction regimes compete in the temperature range below 4.2 K. The temperature at which one regime gives way to another is 2.6 K. The TMR at 1.7 K has been found to be greater than that at 4.2 K. Moreover, at both temperatures, TMR is larger than that predicted by TMR theory for conduction-band electrons. In our case, TMR is mainly caused by carrier reduction with partial compensation by mobility increase. It has also been found that a magnetic field of 5.6 kG has no effect on the activation energies that exist at temperatures higher than 2.6 K, while it increases the lower temperature ones.

Thermal geometric discords in a two-qutrit system

2016 ◽  
Vol 14 (03) ◽  
pp. 1650016 ◽  
Author(s):  
Ya-Li Yuan ◽  
Xi-Wen Hou
Keyword(s):  
Magnetic Field ◽  
Quantum Information ◽  
Magnetic Fields ◽  
Weak Magnetic Field ◽  
Quantum Discord ◽  
Quantum Information Processing ◽  
Thermal State ◽  
Quantum Correlations ◽  
High Dimensional ◽  
Lower Temperature

The investigation of quantum discord has mostly focused on two-qubit systems due to the complicated minimization involved in quantum discord for high-dimensional states. In this work, three geometric discords are studied for the thermal state in a two-qutrit system with various couplings, external magnetic fields, and temperatures as well, where the entanglement measured in terms of the generalized negativity is calculated for reference. It is shown that three geometric discords are more robust against temperature and magnetic field than the entanglement negativity. However, all four quantities exhibit a similar behavior at lower temperature and weak magnetic field. Remarkably, three geometric discords at finite temperature reveal the phenomenon of double sudden changes at different magnetic fields while the negativity does not. Moreover, the hierarchy among three discords is discussed. Those adjustable discords with the varied coupling, temperature, and magnetic field are useful for the understanding of quantum correlations in high-dimensional states and quantum information processing.

Conduction band of InAs

1968 ◽  
Vol 46 (15) ◽  
pp. 1669-1675 ◽  
Author(s):  
Clarence C. Y. Kwan ◽  
John C. Woolley
Keyword(s):  
Magnetic Fields ◽  
Hall Effect ◽  
Valence Band ◽  
Conduction Band ◽  
Infrared Absorption ◽  
Room Temperature ◽  
Impurity Content ◽  
Temperature Measurements ◽  
Energy Separation ◽  
Transverse Magnetoresistance

Measurements of transverse magnetoresistance and Hall effect have been made at 4.2 °K on various In2Se3-doped and In2Te3-doped InAs polycrystalline specimens with magnetic fields up to 3.2 Wb/m2. An analysis of the results gives values of electron concentrations n0 and n1 and mobilities μ0 and μ1 for both the (000) and [Formula: see text] conduction-band minima. From the values of n0 and n1, the energy separation of the (000) and [Formula: see text] minima E01 of pure InAs has been determined to be 0.70 + 0.02 eV and is found to decrease with increasing impurity content, the rate of reduction being 0.13 ± 0.02 eV/at.% selenium and 0.17 ± 0.03 eV/at.% tellurium. Room-temperature measurements of electroreflectance and infrared absorption have also been made, and these indicate that the variation in E01 is due to the movement of the (000) conduction-band minimum relative to the valence band.

Electron Subband Levels of n-Type δ-Doped Quantum Wells under In-Plane Magnetic Fields

1997 ◽  
Vol 11 (09) ◽  
pp. 1195-1207
Author(s):  
E. K. Takahashi ◽  
A. T. Lino ◽  
L. M. R. Scolfaro
Keyword(s):  
Magnetic Field ◽  
Electronic Structure ◽  
Magnetic Fields ◽  
Quantum Well ◽  
Quantum Wells ◽  
Conduction Band ◽  
Electron Energy ◽  
Self Consistent ◽  
Plane Direction ◽  
The Magnetic Field

Self-consistent calculations of the electronic structure of center n-δ-doped GaAs/Al x Ga 1-x As quantum wells under in-plane magnetic fields are presented. The field B is varied up to 20 Tesla for different quantum well widths L w and sheet donor concentrations N D . The magnetic field produces noticeable changes in the energy dispersions along an in-plane direction perpendicular to B. The effects of B are more pronounced for higher electronic subbands. It is found that the diamagnetic shifts increase with increasing L w and/or N D . Contrarily to what has been observed in modulation-doped quantum wells, in these δ-doped systems the electron energy dispersions keep the single conduction band minimum at the center of the Brillouin zone even for intense magnetic fields.

MAGNETIC RESONANCES OBSERVED IN THE HIGH-FIELD MAGNETO-OPTICAL ABSORPTION OF THE QUANTUM ISING FERROMAGNET LiHoF4

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3312-3315
Author(s):  
R. S. EDWARDS ◽  
A. NARDUZZO ◽  
E. LYONS ◽  
L. CHILDRESS ◽  
S. J. BLUNDELL ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Optical Absorption ◽  
Fast Moving ◽  
High Field ◽  
Frequency Range ◽  
Ising Ferromagnet ◽  
Temperature Range ◽  
Magnetic Resonances

The magneto-optical absorption of the quantum Ising ferromagnet LiHoF4 has been measured in the frequency range 38 to 140 GHz, the temperature range 0.5 to 20 K and magnetic fields of up to 15 T. The sample was studied in two orientations, with the external magnetic field aligned perpendicular or parallel to the uniaxial direction, i.e., along the quantum and classical directions. In each case, several families of resonances are observed, including linear EPR branches and a series of non-linear fast moving resonances. We present this data and propose an interpretation for the origin of these resonances.

scholarly journals The Optimization of Jc, Birr, n value, Wires Diameter, and Research of the Dominant Pinning Mechanism for Applications of Undoped MgB2 in Superconducting Multi-section Coils

2020 ◽  
Vol 33 (12) ◽  
pp. 3717-3725
Author(s):  
D. Gajda ◽  
A. J. Zaleski ◽  
A. Morawski ◽  
T. Cetner ◽  
M. Małecka ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Annealing Temperature ◽  
Critical Parameters ◽  
Pinning Mechanism ◽  
N Value ◽  
Superconducting Coils ◽  
Higher Temperature ◽  
Lower Temperature ◽  
The Magnetic Field

Abstract This article discusses the influence of MgB2 wire diameter on critical parameters, dominant pinning mechanism, and n value. Studies were conducted on multifilament MgB2 wires of the 0.84 mm and 0.64 mm diameter. The wires were annealed under 1 GPa isostatic pressure, between 650 and 730 °C. Studies show that the best results (Jc, Birr, n value, and point pinning mechanism) for a 0.64-mm wire were obtained with annealing temperature of 650 °C. However, the best results for wires with a 0.84-mm diameter were obtained with annealing temperature of 730 °C. This research was conducted for exploring the use of MgB2 wires in multi-section superconducting coils, e.g., main coils generating magnetic fields and compensation coils—increasing the homogeneity of the magnetic field. Our research indicates that the main coil made with larger diameter wires should be heated at higher temperature (730 °C). In contrast, compensating coils with smaller diameter wires should be heated at a lower temperature (650 °C).

NEUTRON SCATTERING IN MAGNETIC FIELDS UP TO 17 T

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3390-3390
Author(s):  
K. PROKES ◽  
P. SMEIBIDL ◽  
M. MEISSNER
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Scattering ◽  
Superconducting Magnets ◽  
Superconducting Magnet ◽  
User Program ◽  
Temperature Range ◽  
Sample Position ◽  
High Fields ◽  
Very High

Neutron scattering in magnetic fields can provide important imformation regarding the magnetism of a system under study on microcsopic scale. Although pulse magnets are capable to reach very high fields, for neutron scattering mostly superconducting magnets are used. At present, a split-pair 14.5 T superconducting magnet used for user-program experiments at HMI offers the highest magnetic field for neutron scattering. With Dy-pole tips placed symmetrically around the sample position a 2.5 T enhancement is achieved. The temperature range accessible with such an insert is between 1.8 and 100 K. Temperatures down to 30 mK can be achieved with a dilution stick, which can be inserted into the 14.5 T cryomagnet. In the contribution we report on the latest neutron scattering achievements in magnetic fields obtained at HMI.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

Peculiarity Parameters

1976 ◽  
Vol 32 ◽  
pp. 233-254
Author(s):  
H. M. Maitzen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Theoretical Work ◽  
Observational Evidence ◽  
Rotator Model ◽  
Peculiar Behaviour ◽  
Field Spectrum ◽  
Oblique Rotator ◽  
Ap Stars ◽  
The Way

Ap stars are peculiar in many aspects. During this century astronomers have been trying to collect data about these and have found a confusing variety of peculiar behaviour even from star to star that Struve stated in 1942 that at least we know that these phenomena are not supernatural. A real push to start deeper theoretical work on Ap stars was given by an additional observational evidence, namely the discovery of magnetic fields on these stars by Babcock (1947). This originated the concept that magnetic fields are the cause for spectroscopic and photometric peculiarities. Great leaps for the astronomical mankind were the Oblique Rotator model by Stibbs (1950) and Deutsch (1954), which by the way provided mathematical tools for the later handling pulsar geometries, anti the discovery of phase coincidence of the extrema of magnetic field, spectrum and photometric variations (e.g. Jarzebowski, 1960).

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