Generation of far-infrared radiation by hot holes in germanium and silicon inE ⊥H fields

The experimental results obtained by the investigation of stimulated FIR emission from dopedp-type germanium andp-type silicon by hot holes in crossedE andH fields at = 10 and 80 K are reported. The analysis of the emission intensity fromp-type germanium as a function ofE andH fields permits us to draw a conclusion about the important role of quantization of the energy spectrum of light holes and the contribution of light hole transitions with n = 2 to the amplification of FIR radiation. A new region of generation is demonstrated inp-type germanium under uniaxial stress. The first experimental results on stimulated FIR emission fromp-type silicon are reported.     

Radiation by relativistic dipoles. IV

An analysis is made of radiation emitted by a neutron moving in constant and homogeneous electromagnetic fields (EH whereE=H, andEH whereEH) as a supplement to the classical theory of radiation from a point magnetic moment (a magneton) developed by the authors. The results obtained are found to be in agreement with the radiation theory of Ternov, Bagrov, and others constructed on the basis of the Dirac-Pauli equation. A study is made of the spectral composition and the invariance properties of the total radiation power.Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 63–71, February, 1995.     

Magnetoexciton absorption in coupled quantum wells

A Mott exciton in coupled quantum wells in a transverse magnetic field H is considered. An expression for the exciton spectrum in an arbitrary magnetic field for large separations D between quantum wells containing an electron (e) and a hole (h) is given. The exciton spectrum in a strong magnetic field for different Landau levels at arbitrary D has been calculated. Changes in the parameter D/l, where is the magnetic length, cause rearrangement of the magnetoexciton dispersion curves ℰ(P), where P is the conserved “magnetic” momentum, which is a function of the separation between the electron and hole in the plane of the quantum wells. Off-center (“roton”) extrema occur only for D/l,<(D/l)_cr, where (D/l)_cr is a function of the exciton quantum numbers n and m. The magnetoexciton effective mass in states with magnetic quantum number m=0 monotonically increases with H and D, while in states with m≠0 it is a nonmonotonic function of D/l. The probability of generating an exciton in coupled quantum wells increases with H. Absorption of electromagnetic radiation due to transitions between excitonic levels in coupled quantum wells is discussed. For an exciton containing a heavy hole the oscillator strengths increase with H and the oscillator strengths decrease. Zh. éksp. Teor. Fiz. 112, 1791–1808 (November 1997)     

Magnetooptic measurements of the cyclotron mass and g-factor of light holes in GaAs

An emission line appearing in the hot-luminescence spectrum of GaAs at a frequency shifted from the laser line by the cyclotron energy of light holes is observed and investigated. Analysis of the magnetooscillations of the intensity of this line shows that the line is due to the recombination of a photoexcited electron and a light hole after the hole undergoes energy relaxation between Landau levels. The dependence of the cyclotron mass and g factor of light holes on the hole energy was measured directly and a very strong nonparabolicity of the valence band of GaAs, several times greater than the theoretical estimates, was observed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 11, 766–771 (10 December 1996)     

Electronic properties of a Weyl semimetal in crossed magnetic and electric fields

The study of Weyl semimetals is one of the most challenging problems of condensed matter physics. These materials exhibit interesting properties in a magnetic field. In this work, we investigate the Landau bands and the density of states (DOS) oscillations in a Weyl semimetal in crossed magnetic and electric fields. An expression is obtained for the energy spectrum of the system using the following three different methods: an algebraic approach, a Lorentz shift-based approach, and a quasi-classical approach. It is interesting that the energy spectrum calculated in terms of the quasi-classical approach coincides with the spectrum obtained using the microscopic approaches. An electric field is shown to change the Landau bands radically. In addition, the classical motion of a three-dimensional Dirac fermion in crossed fields is studied. In the case of a Dirac spectrum, the longitudinal (with respect to magnetic field) component of momentum (p _z ∥ H) is shown to be an oscillating function of the magnetic field. When the electric field is v⊥H/c, the Landau levels collapse and the motion becomes fully linear in an unusual manner. In this case, the wavefunction of bulk states vanishes and only states with p _z = 0 are retained. An electric field affects the character of DOS oscillations. An analytical expression is obtained for the quantum capacitance in crossed fields in the cases of strong and weak electric fields. Thus, an electric field is an additional parameter for adjusting the diamagnetic properties of Weyl semimetals.     

Far IR cyclotron resonance and luminescence of hot holes inp-Ge

A survey of techniques and experimental results from the investigation of hot hole effects in germaniumvia their absorption and spontaneous emission in the far IR (FIR) range. The results of a cyclotron resonance absorption investigation of hot holes in crossedE andB fields in a wide wavelength range 0.3 to 2 mm at 40 K are presented. The light hole sub-band overpopulation and the absorption pecularities under streaming conditions are investigated. Mechanisms of FIR emission ofp-Ge at liquid helium temperatures are analysed. A new emission mechanism associated with the crystal lattice emission is revealed and an estimation of FIR phonon-assisted absorption is made. The population inversion of h-l transitions is diagnosed by the effect of flare up of FIR luminescence of hot holes in Ge with an applied magnetic fieldB E, and the FIR radiation gain at l-h transitions is estimated. The different factors affecting the flare up and the gain of FIR radiation, such as the crystallographic orientation of the crossedE andB fields, slight nonorthogonality of theE andB fields, the sample heating during the electric field pulse and the uniaxial stress, are discussed.     

Reciprocity and equivalence in reciprocal and non-reciprocal media through reflection transformations of the current distributions

The electromagnetic wave fields generated by arbitrary electric and equivalent magnetic current distributions are expressed by means of a Maxwell operator in anisotropic, gyrotropic or bianisotropic media. Provided that the constitutive tensorK(r), (which relates the wave-field vectorsD andB toE andH), has in each case the appropriate symmetry in its spatial variation, Lorentz-type reciprocity relations are obtained connecting the given current distributions and their wave fields with a transformed (reflected) set of current distributions and their fields. Reflections are with respect to a plane, a line or a point, depending on the symmetry structure of the constitutive tensor. Modified Lorentz reciprocity appears as a special case of the reflection transformations. A related set of reflection transformations yields equivalence (rather than reciprocity) relationships, in which mirrored current distributions generate mirrored wave fields. Various applications are discussed.     

Remarkable effects of uniaxial stress on stimulated far IR emission from hot holes in germanium in crossed electric and magnetic fields

Stimulated far IR emission due to l-h as well as cyclotron transitions of hot holes in uniaxially stressedp-Ge (P H E) was studied. The results obtained showed the significance of intersub-band hole tunnelling for these mechanisms of generation and may be explained by a change in tunnelling produced by the stress. A considerable expansion of the stimulated light hole cyclotron emission band was observed in a stressed crystal. This expansion allows covering (in one sample) of all generation bands in the light hole cyclotron resonance (CR) masers in unstressedp-Ge, reported so far.     

Spectrum of indirect magnetoexcitons in coupled quantum wells

The indirect Mott exciton (spatially-separated electron and hole) in coupled quantum wells in crossed electric and magnetic fields is discussed. The exciton spectrum is calculated for the case where the distance between the quantum wells of the electron and hole is larger than the exciton Bohr radius. The magnetoexciton creation probability is calculated and its dependence on the electric field is found. The absorption of electromagnetic radiation between the indirect magnetoexciton levels in coupled quantum wells is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 2220–2223 (December 1997)     

Wide-range tunable sub-millimetre cyclotron resonance laser

The results of investigation of cyclotron type stimulated emission processes inp-Ge in strong crossedE B fields are presented. Using the optimumE,B field orientation the spectral range of continuous tuning of the emission line frequency was increased substantially. A tunable sub-millimetre laser with the tuning rangev = 25 to 95cm^–1 ( = 105 to 400m), output power 10 to 100mW and emission linewidthv 0.2cm^–1 is described.     

Hot hole effects in uniaxially stressedp-type germanium under E∥P∥ [1 1 1]

High field behaviour of holes in uniaxially stressedp-type germanium for stressP and the electric fieldE along the [1 1 1] axis is studied. The field dependence of the drift velocity, the frequency dependence of the longitudinal differential mobility and the spectral dependence of the sub-band population for direct hole transitions between the upper and lower splitted sub-bands are calculated by the Monte-Carlo method. A Gunn-type negative differential mobility is demonstrated to appear atP 7 to 8 kbar,E 0.15 to 4 kV cm^–1 in a frequency rangev 0 to 100 GHz. It is shown, that the stimulated emission and current increase observed by I. V. Altuhovet al. [1] cannot be ascribed to the direct hole transitions between the sub-bands because the population inversion of the transitions is absent.     

Soft Component of Emission from Channeled Electrons in a Silicon Crystal

The Tomsk synchrotron has been used to measure the emission spectrum and orientation dependences of the yield of photons with energies much smaller than the emission energy of channeled electrons. The measurements have been performed with a crystal-diffraction spectrometer. For electrons incident along the (110) axis, the radiation intensity in the energy range 30 360 keV exceeds the bremsstrahlung one by almost an order of magnitude. The shape of the emission spectrum does not coincide with that of the bremsstrahlung spectrum. The radiation intensity increases smoothly with the photon energy. The bremsstrahlung spectrum from a disoriented crystalline target is satisfactorily described by the existing theory with phenomenological consideration of the polarization of the medium.     

Exact results of a dimerized S=1 Ising chain with single-ion anisotropy

The dimerized spin-1 Ising chain with both longitude and transverse single-ion anisotropies D_z and D_x is solved exactly by means of a mapping to the spin- Ising chain with the alternating transverse fields and the Jordan-Wigner transformation. The analytical expressions of the quasi-particles’ spectra Λ_k, the minimal energy gap Δ₀ for exciting a fermion quasi-particle, the minimal energy gap Δ_h for exciting a hole, and the ground-state energy E_g are obtained. The phase diagram of the ground state is also given. The results show that the system exhibits a series of quantum phase transitions depending on the dimerization strength of the crystal fields, while the quantum critical points are determined exactly.     

Tunneling conductivity oscillations in a magnetic field in metal-insulator-narrow-gap-HgCdTe structures: The energy spectrum and spin-orbit splitting of 2D states

We study tunneling conductivity oscillations in a magnetic field in narrow-gap p-HgCdTe-oxide-metal (Yb, Al) structures. In tunnel structures with Yb we detect two types of tunneling conductivity oscillations. The first is related to the crossing of the Landau levels of two-dimensional (2D) states localized in the surface quantum well of the semiconductor, and has an energy E _F+eV, where E _F is the Fermi energy of the semiconductor and V is the bias voltage; the second has an energy E _F. We find that in such structures with an asymmetric quantum well there is strong spin-orbit splitting in the spectrum of the 2D states. In p-HgCdTe-oxide-Al tunnel structures the surface potential is much weaker and only oscillations of the first type are observed. We find that in such structures there is only one spin state of the 2D carriers, while the second is pushed into the continuous spectrum because of strong spin-orbit coupling. To analyze the experimental results we calculate the spectrum of 2D states localized in the surface quantum well in a semiconductor with a Kane dispersion law. We find that all the experimental results are in good agreement with the results of calculations. Finally, we discuss the features of “kinematically coupled” states in an asymmetric quantum well. Zh. éksp. Teor. Fiz. 112, 537–550 (August 1997)     

Magnetoplasmon replica in the recombination radiation spectra of a quasi-two-dimensional electron gas in GaAs/AlGaAs quantum wells

The radiative recombination spectra of two-dimensional electrons with free photoexcited holes are investigated for a wide variety of GaAs/ AlGaAs quantum wells, with different thicknesses and electron densities. It is found that for certain, close to integral, filling factors an intense line corresponding to an Auger process — radiative recombination with the emission of an additional magnetoplasmon — appears in the luminescence spectrum. The new line is shifted to lower energies with respect to the zero Landau level, and the magnetic field dependence of the energy splitting between these lines agrees with the theoretical concepts of the dispersion of magnetoplasmon excitations. This makes it possible to estimate the magnetoplasmon energy at the roton minimum. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 8, 539–544 (25 October 1997)     

R branch tuning characteristics of the13CH3F Raman FIR laser

Summary We described a¹³CH₃F Raman laser pumped by a grating tuned 20 atmospheres CO₂ laser. The emission characteristics of the¹³CH₃F laser extends from 14 cm^–1–35 cm^–1 and from 49 cm^–1–72 cm^–1; about 65% of these frequency ranges can be covered with tunable radiation. The characteristics shows a strong dependence on the rotaional quantum numbers of the states involved in the Raman laser transitions and, within each tuning interval, on the frequency offset with respect to the frequencies of resonant transitions. We obtained, at 51 cm^–1, a maximum FIR laser pulse energy of about 800 J (at a pump energy of 200 mJ), corresponding to a photon conversion of about 8%. In some cases we have observed simultaneous emission at a Raman and a cascade frequency. In addition, FIR emission power dependence on¹³CH₃F gas pressure and pump pulse power were investigated for different J quantum numbers.     

Combined polaron states in magnetooptical effects in a quantum well

Combined polaron states in a rectangular quantum well in a strong magnetic field perpendicular to the well plane are discussed. These states are due to interaction between two discrete electron levels with different Landau quantum numbers (n and n ₁) and different size-quantization quantum numbers (m and m ₁) on the one hand and a confined LO phonon on the other under conditions of low temperature when the energy difference between the electronic levelsis equal or close to the energy of the confined LO phonon. The expression for the resonant magnetic field H _res at which a combined polaron is formed contains the energy difference between size-quantized levels, so it is a function of quantum well parameters. The separation ΔE _res between branches in the energy spectrum of a combined polaron and H _res has been calculated as a function of the quantum well width d. The resonant field H _res can be reduced dramatically in comparison with the case m=m ₁. The case of size-quantization with n=n ₁ has been analyzed. The energy difference ΔE _res is in the range (1–5)· 10⁻³ eV. The damping of combined polaron states due to the effect of anharmonicity on the LO phonon has been studied. Interband absorption and features in the reflection spectrum due to interband transitions have been calculated for an arbitrary ratio between the radiative and “phonon” lifetime of a combined polaron have been investigated. Zh. éksp. Teor. Fiz. 116, 1419–1439 (October 1999)     

Reflection and absorption of light by a quantum well in a strong magnetic field under pulsed irradiation

The interaction between a quantum well with a large number of equidistant excited electron energy levels and light is investigated. It is shown that nonsinusoidal oscillations occur in the transmitted, reflected, and absorbed energy fluxes under exposure of the quantum well to irradiation with light pulses. For long pulses whose length γ _l ^?1 is one order of magnitude longer than the time ?/ΔE (where ΔE is the energy level spacing), the oscillation amplitude is small. In the case of narrow pulses when γ _l ^?1 ≤?/ΔE, the oscillation amplitude is comparable to the flux magnitudes. For very narrow pulses with

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, the decaying echo of exciting pulse should be observed at the time intervals 2π?/ΔE. Symmetric and asymmetric pulses are considered. The theory is applicable to narrow quantum wells in a strong magnetic field when the equidistant levels correspond to electron-hole pairs with different Landau quantum numbers.

     

Landau-Level Quantization of the Yellow Excitons in Cuprous Oxide

Lately, the yellow series of P-excitons in cuprous oxide could be resolved up to the principal quantum number n = 25. Adding a magnetic field, leads to additional confinement normal to the field. Thereby, the transition associated with the exciton n is transformed into the transition between the electron and hole Landau levels with quantum number n, once the associated magnetic length becomes smaller than the related exciton Bohr radius. The magnetic field of this transition scales roughly as n^–3. As a consequence of the extended exciton series, we are able to observe Landau level transitions with unprecedented high quantum numbers of more than 75.     

Supertransferred hyperfine magnetic fields at111Cd(←111In) in ferrimagnetic oxides with the spinel structure

The supertransferred hyperfine magnetic fields,H _STHF, at¹¹¹Cd(¹¹¹In) on the tetrahedral sites of the spinel oxides Fe_3-xM_xO₄ (M = Ni or Co) were measured by means of the time differential perturbed angular correlation. The observedH _STHF were analyzed as the sum of the fields transferred from individual B site magnetic ions: 11 kOe/Fe³⁺, 8 kOe/Fe²⁺, 4 kOe/Ni²⁺ and 4 kOe/Co²⁺. A brief discussion is presented on these results in comparison with previous ones onH _STHF at¹¹¹Cd(^111mCd) in rocksalt-type oxides and the one at¹¹¹in in NiFe₂O₄.