Transient photoconductivity in the ferromagnetic semiconductor CdCr2Se4

The transient photoconductive response time of the ferromagnetic semiconductor CdCr₂Se₄ was measured to be smaller than 90 ps, the response time of the scope. The measurements were performed at room temperature (300 K) for 0.53 and 1.06 m excitations using a mode locked frequency-doubled YAG laser.     

Propagation of electromagnetic waves in the magnetic semiconductor CdCr2Se4

Saratovskii State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 7, pp. 891–896, July, 1989.     

Quantum oscillations in confined and degenerate Fermi gases. I. Half-vicinity model

We propose an analytical model for the prediction and accurate calculation of size and density dependent quantum oscillations in thermodynamic and transport properties of confined and degenerate Fermi gases. Our model considers only half-vicinity states of Fermi level. We show that the half-vicinity model quite accurately estimates quantum oscillations depending on confinement and degeneracy. Periods of quantum oscillations are even analytically expressed for one-dimensional case. Furthermore, similarities between functional behaviors of total occupancy variance and conventional density of states functions at Fermi level are discussed.     

Quantum oscillations in the underdoped cuprate YBa2Cu4O8

We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85 T. There is a clear signal, periodic in inverse field, with frequency 660+/-15 T and possible evidence for the presence of two components of slightly different frequency. The quasiparticle mass is m(*)=3.0+/-0.3m(e). In conjunction with the results of Doiron-Leyraud et al. for YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a general feature of underdoped copper oxide planes and provide information about the doping dependence of the Fermi surface.     

Magnetoresistance and Hall effect of the magnetic semiconductor HgCr2Se4 in strong magnetic fields

The giant decrease of the electrical resistance of HgCr₂Se₄ (more than by a factor of 200) caused by magnetic field-induced changes in the carrier mobility and concentration, the quadratic dependences of magnetoresistance and normal Hall constant on magnetic induction in the paramagnetic region, as well as the deviations from these dependences observed to occur as one approaches the Curie temperature, are discussed within a model involving carriers of several types (holes in the valence band, electrons localized at ferron-type impurity centers, and electrons hybridized in the impurity and conduction bands). Fiz. Tverd. Tela (St. Petersburg) 39, 848–852 (May 1997)     

Density-functional-theory investigation of pressure induced semiconductor-metal transitions in the ferromagnetic semiconductor HgCr2Se4

We investigate the electronic structures of the ferromagnetic semiconductor HgCr(2)Se(4) by using a modified Becke and Johnson exchange potential. The energy gap calculated with the experimental lattice structure is in good agreement with the experimental value. When the pressure reaches 9.0 GPa, HgCr(2)Se(4) becomes a so-called spin gapless semiconductor due to the closure of the spin non-conservation energy gap, and when the pressure increases to 11.4 GPa, the spin conservation energy gap closes, leading to a semiconductor-semimetal transition.     

Nonlinear Faraday effect near the fundamental absorption edge in the ferromagnetic semiconductor CdCr2 Se4

A sharp increase of the Faraday rotation with increasing incident radiation power is observed in a band near the fundamental absorption edge of the ferromagnetic semiconductor CdCr₂ Se₄. The magnitude of the effect is a nonmonotonic function of the radiation intensity. The effect is explained by narrowing of an excitonic resonance as a result of screening of the internal electric fields by photoexcited carriers. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 409–413 (25 September 1997)     

Quantum oscillations in confined and degenerate Fermi gases. II. The phase diagram and applications of half-vicinity model

For part I see DOI: 10.1016/j.physleta.2018.02.006. Size and density dependent quantum oscillations appear in Fermi gases under strong confinement and degeneracy conditions. We provide a universal recipe that explicitly separates oscillatory regime from non-oscillatory (stationary) one. A phase diagram representing stationary and oscillatory regimes on degeneracy-confinement space is proposed. Analytical expressions of phase transition interfaces are derived. The critical point, which separates entirely stationary and oscillatory regions, is determined and its dependencies on aspect ratios are examined for anisometric domains. Accuracy of the half-vicinity model and the phase diagram are verified through the quantum oscillations in electronic heat capacity and its ratio to entropy.     

中子星中简并电子气体的临界磁化

中子星内部的电子处于高度简并或完全简并的状态,电子磁矩(包括内禀磁矩和朗道反磁矩)的取向不是随机的,而是呈现出极强的磁化行为.考虑了磁化后的磁诱导方程要改写,改写后的方程添加了新的磁场生成项,更重要的改变是等效磁扩散系数变小了(顺磁情况),在临界情况(等效扩散系数等于零),磁场在磁生成项的作用下增加直到抑制机理出现,朗道反磁矩就是在这个时候变得越来越重要.磁场增加的最终结果使中子星局域磁场成为振荡的,对外看来有可能成为磁星. 关键词： 中子星 简并 磁化     

EXAS study of the promising semiconductor material Ga2Se3

Ga₂Se₃, a promising material for absorbing layers of high-efficient solar cells, is studied by EXAFS spectroscopy. Structural data (e.g., interatomic distances and coordination numbers) are obtained for the local environment of gallium and selenium, and are compared to modeling calculations performed using FEFF-8 software.     

Quantum oscillations in the underdoped cuprate

Quantum oscillations occur via Landau quantisation of the quasiparticle in a Fermi liquid at low temperature. In the light of currently popular notions their detection in the ortho-II-YBa₂Cu₃O_6.45 and YBa₂Cu₄O₈ crystals is inconsistent with this. We explain this in terms of multichannel Kondo model of the underdoped cuprate.     

Quantum statistics of the degenerate parametric amplifier

From the quantum mechanics and the quantum optics point of view the problem of the time-dependent Hamiltonian which describes the degenerate parametric amplifier is presented. Under a certain integrability condition the solution of the Heisenberg equations of motion is given. The wave function for both the Schrödinger picture and quasi-coherent states, as well as the Green's function is obtained. The Glauber second order correlation function, and the squeezing and higher order squeezing is examined. The quasi-probability distribution function is also considered.     

Quantum degenerate exciton-polaritons in thermal equilibrium

We study the momentum distribution and relaxation dynamics of semiconductor microcavity polaritons by angle-resolved and time-resolved spectroscopy. Above a critical pump level, the thermalization time of polaritons at positive detunings becomes shorter than their lifetime, and the polaritons form a quantum degenerate Bose-Einstein distribution in thermal equilibrium with the lattice.     

Photoluminescence in YbGa2Se4 and YbGa2Se4:Nd3+ single crystals

The excitation and photoluminescence spectra of YbGa₂Se₄ and YbGa₂Se₄:Nd³⁺ single crystals recorded at different temperatures and neodymium concentrations have been investigated. The photoluminescence spectrum exhibits intracenter luminescence lines of the Nd³⁺ ion in wavelength ranges of 0.804?C0.84, 0.88?C0.92, 0.96?C0.996, and 1.06?C1.12 ??m against a broadband emission background. These ranges are related, respectively, to the ⁴ F _5/2-⁴ I _9/2, ⁴ F _3/2-⁴ I _9/2, ⁴ F _5/2-⁴ I _11/2, and ⁴ F _3/2-⁴ I _11/2 transitions.     

Quantum efficiency for degenerate p-type photoluminescence and electroluminescence in GaAs crystals2

The radiative lifetime and the internal quantum efficiency for the degenerate p-type photoluminescence and the electroluminescence in GaAs crystals have been investigated with a simplified model of degenerate semiconductors in which the recombination constant B is approximately proportional to the ?$\text{5}\text{8}$power of the hole concentration. It is suggested that the radiative lifetime reaches a minimum at some hole concentration, in good agreement with the prediction of Dumke. At 77 K, the internal quantum efficiency exhibits a maximum, found to be 100% at 5 × 10¹⁸ cm^?3 for p-type GaAs crystals, in perfect agreement with experiments of Cusano, and for p-n GaAs junction crystals η_int, _max = 60% at 3 × 10¹⁸cm^?3. Finally, it is noted that in degenerate p-type GaAs crystals, the internal quantum efficiency increases linearly with increasing temperatures.