scholarly journals INTERSUBBAND MAGNETOPHONON RESONANCES IN QUANTUM CASCADE STRUCTURES

2002 ◽  
Vol 16 (20n22) ◽  
pp. 2952-2955
Author(s):  
D. SMIRNOV ◽  
O. DRACHENKO ◽  
J. LEOTIN ◽  
H. PAGE ◽  
C. BECKER ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Tunneling Current ◽  
Applied Bias ◽  
Acoustic Phonons ◽  
Quantum Oscillations ◽  
Quantum Cascade ◽  
Electron Relaxation ◽  
Magnetophonon Resonance ◽  
Quantum Cascade Structures

We report on magnetotransport measurements of GaAs/GaAlAs quantum cascade structures in magnetic fields up to 62 T parallel to the current. We observe novel quantum oscillations series in tunneling current that are periodic in reciprocal magnetic field and have field positions independent of the applied bias. These oscillations are explained as intersubband magnetophonon resonance due to electron relaxation by emission of optical or acoustic phonons.

THE STUDY OF THE MAGNETIC BREAKDOWN EFFECT AS A FUNCTION OF ANGLE IN THE ORGANIC CONDUCTOR K- (BEDT-TTF)2Cu(NCS)2 IN HIGH MAGNETIC FIELDS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3355-3359
Author(s):  
I. MIHUT ◽  
C. C. AGOSTA ◽  
C. H. MIELKE ◽  
M. TOKOMOTO
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spin Splitting ◽  
High Magnetic Fields ◽  
Organic Conductor ◽  
Cross Sectional ◽  
Tank Circuit ◽  
Quantum Oscillations ◽  
Magnetic Breakdown ◽  
Splitting Factor

The magnetic breakdown effect can be seen by the growth of new frequencies in the quantum oscillations in clean metals as a function of magnetic field. We have studied the variation of the amplitudes in the quantum oscillations in the resistance (the Shubnikov-de Haas effect) as a function of angle in the quasi-two dimensional-organic conductor κ-(BEDT-TTF)2Cu(NCS)2. The measurements were made by means of a radio frequency (rf) tank circuit (~ 50 MHz) at very high magnetic fields(50T-60T) and low temperature(500 mK). The geometry of the rf excitation we used excited in-plane currents, and therefore we measured the in-plane resistivity. In contrast to conventional transport measurements that measure the inter-plane resistivity, the in-plane resistivity is dominated by the magnetic breakdown frequencies. As a result we measured much higher breakdown frequency amplitudes than conventional transport experiments. As is expected, the angular dependence of the Shubnikov-de Haas frequencies have a 1/cosθ behavior. This is due to the change of the cross sectional area of the tubular Fermi surface as the angle with respect to the magnetic field is changed. The amplitude of the oscillations changes due to the spin splitting factor which takes into account the ratio between the spin splitting and the energy spacing of the Landau levels which also has 1/cosθ behavior. We show that our data agree with the semi-classical theory (Lifshitz-Kosevich formula).

Transporteigenschaften und Quantenoszillationen von Te-und Sn-dotiertem Bi94Sb6 / Transport Properties and Quantum Oscillations of Te- and Sn-Doped Bi94Sb6

1975 ◽  
Vol 30 (8) ◽  
pp. 1071-1083
Author(s):  
G. Schneider ◽  
R. Trommer
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transport Properties ◽  
Thermoelectric Power ◽  
Effective Mass ◽  
Quantum Oscillations ◽  
Mobility Tensor ◽  
Mass Tensor ◽  
Approximate Composition ◽  
Shubnikov De Haas Oscillations

Abstract Electronic transport properties of undoped, Te- and Sn-doped Bi-Sb-alloys of approximate composition Bi94Sb6 were measured within the temperature range 10-300 K. Besides the electrical conductivity and thermoelectric power the magnetoresistance, the Hall effect and the thermoelectric power in a magnetic field were investigated. Measurements in low magnetic fields yield the mobility tensor for Te-doped samples and in connection with the Shubnikov-de Haas oscillations in higher magnetic fields the effective mass tensor of the electrons. Corresponding investigations on Sn-doped p-conducting samples in this paper give the mobility tensors of light and heavy holes and approximately the effective mass tensor. Here quantum oscillations of the thermoelectric power in a magnetic field were analysed.

QUANTUM CASCADE NANOSTRUCTURES UNDER HIGH MAGNETIC FIELD

2009 ◽  
Vol 23 (12n13) ◽  
pp. 2861-2866
Author(s):  
N. PÉRÉ-LAPERNE ◽  
L. A. DE VAULCHIER ◽  
Y. GULDNER ◽  
C. SIRTORI ◽  
V. BERGER
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
Dark Current ◽  
Phonon Scattering ◽  
Interface Roughness ◽  
Landau Levels ◽  
Hot Carriers ◽  
Quantum Cascade ◽  
Transport Measurements ◽  
Quantum Cascade Structures

Magneto-transport measurements have been performed on two quantum cascade structures, a laser and a detector. These experiments lead to determine the different scattering processes involved in these devices. In the lasers we find both an interface roughness mechanism and LO-phonon scattering of hot carriers in the upper state's Landau levels. In detectors we discover that an inelastic mechanism increase the dark current whereas an elastic one limits the detectivity.

Influence of electron–electron scattering on electron relaxation rates in three and four-level quantum cascade lasers in magnetic fields

2007 ◽  
Vol 279 (2) ◽  
pp. 330-335 ◽  
Author(s):  
Božidar Novaković ◽  
Jelena Radovanović ◽  
Aleksandra Mirčetić ◽  
Vitomir Milanović ◽  
Zoran Ikonić ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Electron Scattering ◽  
Quantum Cascade Lasers ◽  
Relaxation Rates ◽  
Quantum Cascade ◽  
Electron Relaxation ◽  
Cascade Lasers

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.

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