Showing papers on "Landau quantization published in 1979"
TL;DR: In this article, the relativistic treatment of photons by electrons in a strong magnetic field is performed for electrons in the lowest Landau level by specializing to the nonrelativistic region.
Abstract: The differential cross section for scattering of photons by electrons in a strong magnetic field is calculated The relativistic treatment is performed for electrons in the lowest Landau level By specializing to the nonrelativistic region, cross sections for Thomson scattering are given for an arbitrary direction of the photon with respect to the magnetic field These results are in agreement with previous calculations The relativistic cross sections are numerically calculated to compare them explicitly with the nonrelativistic case and to present numerical values which can be used, for instance, in practical applications to neutron stars
188 citations
TL;DR: In this paper, an effective Hamiltonian, acting in the eightfold space of the valence band and the lowest conduction band of a zinc-blende-type material, is constructed by invariant expansion.
Abstract: Quantum resonances in the valence bands of semiconductors under uniaxial stress provide very detailed information on the band parameters if the experimental data can be analyzed on the basis of an adequate theoretical model. Such a model has been developed for and applied to Ge by Hensel and Suzuki and yielded high-precision band parameters for this material. The theory which is based on the invariant expansion of the valence-band Hamiltonian and makes use of the symmetry of the diamond lattice fails, however, to explain similar experiments for InSb. The reason for this failure is twofold: The reduced symmetry of the zinc-blende lattice makes it necessary to consider inversion-asymmetry-induced contributions to the effective Hamiltonian; the small gap of InSb requires an exact treatment of the couplings between valence band and lowest conduction band. Here we present a theory to overcome these difficulties. An effective Hamiltonian, acting in the eightfold space of the valence band and the lowest conduction band of a zinc-blende-type material, is constructed by invariant expansion. For this purpose the method of invariants is extended to the cross space between valence band and conduction band on the basis of the angular momentum calculus. The Hamiltonian describes the Landau levels of valence and conduction bands under uniaxial stress for magnetic fields (parallel to the stress) along the high-symmetry [001], [111], and [110] directions. Since the Hamiltonian is constructed on group-theoretical grounds, the eigenstates can be classified according to their transformation properties, and selection rules are given for both inter- and intraband transitions.
131 citations
TL;DR: In this paper, a theory of the magnetoresistance of disordered carbons is presented and applied to experimental results on carbon fibers and glassy carbon, and four structure-dependent parameters are used to fit the resistivity as a function of temperature, field strength, and orientation of the sample in the field.
Abstract: A theory of the magnetoresistance of disordered carbons is presented and applied to experimental results on carbon fibers and glassy carbon. The important features of the model include (a) a two-dimensional band structure and density of states, (b) a shallow acceptor level due to defects, (c) collision-broadened Landau levels, and (d) an extra density of states in the $m=0$ Landau level to account for the effects of partial three-dimensional ordering of the graphitelike layers. The negative magnetoresistance results from field-induced changes in the density of states which lead to an increase in the carrier concentration with field. Four structure-dependent parameters are used to fit the resistivity as a function of temperature, field strength, and orientation of the sample in the field. Approaches to improving the model are discussed.
52 citations
TL;DR: In this paper, the theory of free-carrier absorption in nondegenerate semiconductors is extended to take into account quantizing magnetic fields in the presence of a magnetic field.
Abstract: The theory of free-carrier absorption in nondegenerate semiconductors is extended to take into account quantizing magnetic fields In the presence of a magnetic field, the behavior of the free-carrier absorption depends not only upon the magnitude of the magnetic field but also upon the polarization of the electromagnetic field relative to the magnetic field direction For electromagnetic radiation polarized transverse to the magnetic field, the phenomenon of free-carrier absorption merges into that of cyclotron resonance, which has been extensively reported in the literature However, when the radiation is polarized parallel to the magnetic field, the absorption depends critically on the mechanisms by which the carriers are scattered in the semiconductor When acoustic phonon scattering is dominant, we find that the free-carrier absorption is an oscillatory function of the magnetic field which increases in magnitude with the magnetic field The oscillations only occur when the photon frequency $\ensuremath{\Omega}$ is greater than the cyclotron frequency of the carriers When $\ensuremath{\Omega}l{\ensuremath{\omega}}_{c}$ the free-carrier absorption is predicted to increase linearly with the magnetic field The magnetic-field dependence of the free-carrier absorption is explained in terms of phonon-assisted transitions between the various Landau levels of the carriers
41 citations
IBM1
TL;DR: In this paper, the subband structure and the intersubband optical absorption spectrum are calculated in $n$-channel inversion and accumulation layers on the Si (100) surface in magnetic fields tilted from the direction normal to the surface.
Abstract: The subband structure and the intersubband optical-absorption spectrum are calculated in $n$-channel inversion and accumulation layers on the Si (100) surface in magnetic fields tilted from the direction normal to the surface. An approximation scheme based on the local-density-functional theory is employed. Effects of magnetic fields on the exchange-correlation potential are completely neglected. Combined intersubband-cyclotron transitions between different Landau levels associated with the ground and excited subbands are allowed in addition to the main transition between the same Landau levels. When the amplitudes of the combined resonances are sufficiently small, they are not affected by the depolarization effect, while the main transition is fully influenced and its position is shifted from the corresponding subband energy separation. This is shown to be also true of accumulation layers, where the subband structure is very complicated because higher quasicontinuum subbands lie close to the ground and the first excited subband. The agreement between the theory and recent experiments of Beinvogl and Koch is satisfactory concerning relative positions of the main and combined transitions in accumulation layers. This indicates that our calculations of both the depolarization effect and the subband energy separations are essentially correct. There remain disagreements especially concerning amplitudes of the combined resonances.
38 citations
37 citations
TL;DR: In this paper, the reabsorption of curvature radiation from relativistic electrons moving along curved magnetic field lines is discussed, and the optical depth for the ray path is calculated by use of the Einstein coefficients.
Abstract: The reabsorption of curvature radiation, i.e. radiation from relativistic electrons moving along curved magnetic field lines, is discussed. The optical depth for the ray path is calculated by use of the Einstein coefficients. It is shown that the optical depth becomes negative (maser effect) if transitions between Landau levels are absent. However, maser action is ineffective if the energy density of the relativistic particles is less than that of the magnetic field. For pulsar radio emission the magnetic energy density is assumed to exceed the particle energy density, so the observed emission cannot be coherent curvature radiation.
36 citations
TL;DR: In this paper, a detailed study of the energy relaxation in n-InSb has shown that the total intensities observed are well described with hot electron distribution functions, governed by an interplay of electron-electron scattering and optical phonon emission.
17 citations
TL;DR: In this paper, sound attenuation in bismuth at low temperature has been measured under the conditions: the longitudinal sound wave vector q is applied along the trigonal axis and the field H is parallel to a trigonal-bisectrix plane.
Abstract: The sound attenuation in bismuth at low temperature has been measured under the conditions: the longitudinal sound wave vector q is applied along the trigonal axis and the field H is parallel to a trigonal-bisectrix plane. For q ∧ H =88.0°±0.3° and 92.2°±0.3°, a quite large attenuation peak has been found, which is due to the second and third lowest Landau levels of the electrons in the degenerated non-principal electron pockets. Its attenuation coefficient α( T , H p ) shows fairly strong temperature dependence and frequency dependence as compared with those in other orientations. A theoretical analysis is presented to explain a part of the anomalies.
15 citations
TL;DR: In this article, it was shown that the singularity spectrum of the phase space integral associated with any partially ordered Landau diagram is confined to a variety defined by a set of modified Landau equations.
Abstract: It is shown that the singularity spectrum of the phase space integral associated with any partially ordered Landau diagram is confined to a variety defined by a set of modified Landau equations. These equations are similar to the ordinary Landau equations but involve limiting procedures. The variety defined by the modified equations coincides with the variety defined by the ordinary equations except at points calledu=0 points. Next the causal parts of the sets defined by the modified Landau equations are defined, in a natural way, and it is conjectured that the singularity spectrum of theS-matrix is confined to the union of the causal parts of the singularity spectra of the phase space integrals. An analogous conjecture on general bubble diagram functions asserts that the singularity spectrum of each of these functions is confined to sets defined by the modified Landau equations augmented by appropriate positive-α and negative-α conditions. Generalized Landau equations are introduced. These equations do not involve limiting procedures, but provide a useful partial characterization of the sets defined by the modified Landau equations augmented by these positive-α and negative-α conditions.
10 citations
TL;DR: In this paper, a hot electron theory is applied to Landau levels of MOS inversion layers as the first example of the theory for extremely quantized systems, where the energy gain from drain fields and the energy loss to phonons are formulated in the self-consistent Born approximation.
Abstract: A hot electron theory is applied to Landau levels of MOS inversion layers as the first example of the theory for extremely quantized systems. The energy gain from drain fields and the energy loss to phonons are formulated in the self-consistent Born approximation. A difference between the electron temperature and the lattice temperature in Landau levels is calculated by balancing these two energy terms. A larger temperature difference is expected for a larger Landau index and is almost independent of the position where the Fermi level lies. The typical temperature rises are 1.4 K for N =0, 3.0 K for N =1, 4.1 K for N =2 and 5.0 K for N =3, when the applied electric field is 20 V/cm, the applied magnetic field is 140 kOe and the lattice temperature is 1.4 K. The observed temperature rises are little lower than the theoretical results.
TL;DR: In this paper, the second derivative signals of the magnetoresistance utilizing magnetic field modulation technique and analysis using the empirical formula obtained by Stradling and Wood were measured between 58 and 235 K in n-InSb with carrier concentrations 3.9 ×10 13 ∼8.3 ×10 14 cm -3.
Abstract: New method is described to investigate the damping factor \barγ which represents the exponential decay of the magnetophonon resonance amplitude in the inverse magnetic field. The method is based on measurement of the second derivative signals of the magnetoresistance utilizing magnetic field modulation technique and analysis using the empirical formula obtained by Stradling and Wood. Measurements are performed between 58 and 235 K in n-InSb with carrier concentrations 3.9 ×10 13 ∼8.3 ×10 14 cm -3 . The observed temperature, impurity and carrier concentration dependence of \barγ ∝( T n s 2 / n ) 1/4 at T <160 K indicates that the dominant process is the band tailing effect. A shift of the extremal position to higher magnetic field is observed. The shift is found to be larger for samples with larger damping factor \barγ. A tentative interpretation for the shift is made in terms of Landau level shift induced by the real part of the electron self-energy.
TL;DR: In this paper, the authors studied the first-order time-dependent perturbation theory of charged-particle scattering by a potential V(r) in the simultaneous presence of a quantising magnetic field and a laser field, both directed along the z axis, and found that the transition probabilities and scattering cross sections exhibit resonant behavior at the zeros of Ki2+2m(ni-nf) omega c/h(cross)+2ml omega 0/h (cross)
Abstract: Charged-particle scattering by a potential V(r) in the simultaneous presence of a quantising magnetic field and a laser field, both directed along the z axis, is studied in first-order time-dependent perturbation theory. Transition probabilities and scattering cross sections are found to exhibit resonant behaviour at the zeros of Ki2+2m(ni-nf) omega c/h(cross)+2ml omega 0/h(cross), where Ki is the wavenumber of the free motion (along z) in the initial state, ni and nf the principal quantum numbers of the initial- and final-state Landau levels, omega c the cyclotron frequency, l=0, +or-1, and +or-2,..., and omega 0 the laser field frequency.
TL;DR: In this article, sound attenuation in Bi 1- x Sb x alloys has been measured under the condition that the magnetic field vector H is nearly perpendicular to the sound wave vector q.
Abstract: The sound attenuation in Bi 1- x Sb x alloys has been measured under the condition that the magnetic field vector H is nearly perpendicular to the sound wave vector q . Quite unlike bismuth, the quantum oscillations with very large amplitudes and with the line shape like the density of state curve were observed. Particularly, for q parallel to a bisectrix axis, the oscillations take the form of a deep dip whenever the Landau level crosses the Fermi level. These anomalies are compared with a tentative theory taking into account of an effect of random diffractions of the sound wave propagation direction due to a spatial inhomogeneity of antimony concentration. The large humps can be partially explained by the theory but the deep dips cannot be explained at all.
TL;DR: Shubnikov-de Haas oscillations have been studied in n -channel silicon MOSFETs in magnetic fields up to 35 T as mentioned in this paper, where the shape of the conductivity peaks becomes asymmetric and the conductivities from whole regions of the Landau level spectrum is suppressed by the magnetic field.
TL;DR: In this article, the temperature dependence of radio frequency size effect (RFSE) signals was observed in aluminium using both the parallel and tilted field geometries, and the results compared with those obtained from surface Landau level (SLL) experiments and also from theoretical calculations.
Abstract: The temperature dependence of radio frequency size effect (RFSE) signals was observed in aluminium using both the parallel and tilted field geometries. Electron-phonon collision frequencies were obtained for electrons on different regions of the Fermi surface and the results compared with those obtained from surface Landau level (SLL) experiments and also from theoretical calculations. Collision frequencies were obtained from orbits near the (100) and (111) limiting points of the second zone hole surface and also from orbits around the central (100) section of the zone hole surface and the (100), (111) and (110) sections of the third zone electron surface.
TL;DR: In this article, the effect of the exchange interaction between spin of the mobile carriers and that of localized paramagnetic atoms on the magnetic levels energetic structure is studied in wide gap semiconductors.
TL;DR: In this article, a physical meaning of the higher-order Landau mode is proposed from the theoretical calculation of the dispersion relation, where the authors show that when the two-temperature mode merges into one of the next higher order Landau modes in the region ω/ω p < 1 (ω p : electron frequency) as the temperature of the small high energy tail in the velocity distribution increases.
Abstract: A physical meaning of the higher-order Landau mode is proposed from the theoretical calculation of the dispersion relation. When the plasma is composed of two electron temperatures, the dispersion relation of the two-temperature mode (the modified fundamental Landau mode) suddenly merges into one of the next higher-order Landau modes in the region ω/ω p <1 (ω p : electron plasma frequency) as the temperature of the small high energy tail in the velocity distribution increases.
TL;DR: In this paper, the thermodynamic properties of semimetals in high transverse magnetic fields are considered, and an excitonic phase is formed at the highest occupied Landau level.
Abstract: The thermodynamic properties of two-dimensional semimetals in high transverse magnetic fields are considered. Thermodynamic characteristics are calculated in the Hartree-Fock approximation, when correlation phenomena are negligible. The electron density appears to jump as the magnetic field H changes. It is found that an excitonic phase is formed at the highest occupied Landau level.
TL;DR: In this article, a non-singular spherically symmetric and separable copy of the vacuum in Landau gauge for SU(2) Yang-Mills theories was given.
TL;DR: In this article, a strong line was observed in the far-infrared absorption spectrum of linearly polarized light with E perpendicular to B and E//B in n-type HgTe in the Voigt configuration.
Abstract: A strong line was observed in the far-infrared absorption spectrum of linearly polarized light with E perpendicular to B and E//B in n-type HgTe in the Voigt configuration. Since the selection rules exclude plasma-shifted cyclotron resonance absorption for E//B, it is postulated that the transition involves a resonant acceptor state and a Landau level of the continuum.
TL;DR: In this article, the lifetime of the first excited Landau level of n-GaAs was determined from a combination of measurements of far infrared cyclotron resonance induced absorption and conductivity change.
TL;DR: In this paper, the authors studied the thermoelectric power at high magnetic fields in the quantum-limit, when hωc > >kBT, ωc being the cyclotron frequency.
01 Jan 1979
TL;DR: In this article, the spin flip Raman scattering (SFRS) incident light of wavevector and frequency ωi interacts via spin orbit coupling with spins in an external magnetic field H 0, producing a spin flip which scatters the light to wavevector \({{k}}_{s}} and frequencyωs, where ωs−ωi = ±gμsH0/ħ.
Abstract: In spin flip Raman scattering (SFRS) incident light of wavevector \({{\vec{k}}_{i}}\) and frequency ωi interacts via spin orbit coupling with spins in an external magnetic field H0, producing a spin flip which scatters the light to wavevector \({{\vec{k}}_{s}}\) and frequency ωs, where ωs−ωi = ±gμsH0/ħ. The ± signs refer respectively to the Stokes and anti-Stokes components and correspond to oppositely directed spin reversals. This process was first suggested by Yafetl following a treatment by Wolff2 of Raman scattering from Landau levels in a semiconductor. SFRS was first observed for conduction electrons in InSb3 where the very large g-value (~50) led to tuneable spin flip Raman lasers.4 It was first observed for bound donors in CdS by Thomas and Hopfield.5 SFRS has also been applied in a number of experiments to the study of velocities6 and diffusional motion of donor electrons in semiconductors.7–9 The diffusional motion appears as a contribution Dq2 to the SFRS linewidth. In these previous studies the Dq2 term was related to the diffusion of charge, while in this paper we report the observation of spin diffusion arising from the exchange interaction between bound donors, without any charge transport.
01 Jan 1979
TL;DR: In this article, the cyclotron resonance of intrinsic electrons in the conduction band was observed at room temperature in pulsed high magnetic fields up to the megagauss range.
Abstract: Recently, many studies have been made of the valence band structure of Te [1]. As for the conduction band, however, much less experimental data have been obtained, because Te crystals are always p-type in the extrinsic region at low temperature. Previous studies of the conduction band structure have been made mainly through the interband magneto-absorption [2] and the cyclotron resonance [3] or the Shubnikov-de Haas effect [4] on the surface inversion layers. In undoped Te crystals, the Hall coefficient changes the sign at about 200 K, as the intrinsic carriers are thermally excited across the forbidden gap, reflecting the fact that the mobility of electrons is larger than that of holes [5]. Therefore, at temperature above 200 K, we would observe the cyclotron resonance of intrinsic electrons in the conduction band, if ωcτ is large enough in high magnetic field [6]. In this paper, we report the cyclotron resonance in Te which was observed at room temperature in pulsed high magnetic fields up to the megagauss range [7].
TL;DR: In this paper, the integral equation for the Green's function of the LOCR was solved exactly, and the resulting energy levels and their corresponding oscillator strength were calculated by talking into account of shallow impurities, the spin orbit coupling and the nonparabolicity of the band structure of InSb.
TL;DR: In this article, it was shown that the weak field expansions of the thermodynamic properties of an electron gas in a uniform magnetic field at T = 0 K do not exist, and the same holds for both non-interacting and interacting electron gases.
TL;DR: In this article, several parameters of the Landau Free Energy Function of TTF-TCNQ are calculated taking into account the real atomic structure, and it is shown that the coupling between longitudinal translations and molecular rotations (librons) on neighbouring chains may provide a suitable mechanism for the establishment of the transverse period between 53K and 38K.
Abstract: Several parameters of the Landau Free Energy Function of TTF-TCNQ are calculated taking into account the real atomic structure. It is shown that the coupling between longitudinal translations (CDW’s) and molecular rotations (librons) on neighbouring chains may provide a suitable mechanism for the establishment of the transverse period between 53K and 38K. The behaviour of Cp in the vicinity of the two close phase transition is studied.
01 Jan 1979
TL;DR: In this paper, the authors consider a long range magnetic environment with a strong magnetic field along the z-axis, such that only one Landau level for one spin orientat ion is occupied.
Abstract: We consider a th ree-d imens iona l e l e c t r o n gas wi th a cons tan t ( long range) i n t e r a c t i o n in the plane perpend i cu la r to the magnetic f i e l d . We l i m i t ourselves to a strong magnetic f i e l d along the z-axis, such that only one Landau level for one spin orientat ion is occupied. Let be an index for the degeneracy of the Landau level and ~. (~) forward (backward) moving electrons along the zaxls. The Hamiltonian of the system is1 ÷ + ÷ #