Microwave-Induced Magneto-Intersubband Scattering in a Square Lattice of Antidots

JETP Letters - The effect of microwave radiation on low-temperature electron magnetotransport in a square antidot lattice with a period of d ≈ 0.8 µm based on a GaAs quantum well with...     

Two-dimensional antiferromagnetic correlations in an La<Subscript>1.4</Subscript>Sr<Subscript>1.6</Subscript>(Mn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>)<Subscript>2</Subscript>O<Subscript>7</Subscript> single crystal

The temperature and field dependences of the magnetization, the electrical resistivity, and the magnetostriction of bilayer lanthanum manganite La_1.4Sr_1.6Mn₂O₇ single crystals and cobalt-doped La_1.4Sr_1.6(Mn_0.9Cu_0.1)₂O₇ are measured. The magnetostriction of the cobalt-doped compound increases as compared to the initial La_1.4Sr_1.6Mn₂O₇ compound, and the magnetization and the magnetoresistance of the former compound change substantially. Powder and single-crystal neutron diffraction patterns are used to detect ferromagnetic ordering in La_1.4Sr_1.6(Mn_0.9Co_0.1)₂O₇ at a temperature below T _C ~ 45(2) K, and this ordering coexists with antiferromagnetic correlations, which develop at temperatures below T _C ~ 80(5) K.     

Microwave photoresistance of a two-dimensional electron gas in a ballistic microbar

The effect of millimeter microwave radiation on the electron transport of two-dimensional (2D) ballistic microbars formed on the basis of individual GaAs quantum wells at a temperature of T = 4.2 K in magnetic fields B < 0.6 T has been investigated. Differences have been revealed in the magnetic field dependences of the microwave photoresistance of a 2D electron gas in Hall bars with a length L and a width W for the cases L, W > l _p and L, W < l _p , where l _p is the electron mean free path for momentum. The microwave photoresistance in macroscopic bars (L, W > l _p ) is a periodic alternating function of the inverse magnetic field; in microbars (L, W < l _p ), it is a periodic positive function of 1/B. The experimental results indicate that the mechanisms of the microwave photoresistance of a 2D electron gas are different for macroscopic and microscopic bars.     

Numerical-graphical method for determining characteristics of damaged viscoelastic materials

A method for determining the material functions of nonlinear endochronic theory of aging viscoelastic materials (NETAVEM) with preliminary mechanical damage was developed. The proposed method is based on an analysis of the differences between two graphs of the stress dependence on time obtained in tension with the same constant speed of two specimens made of the same filled polymer material. One of the specimens was not preloaded, and the other was preloaded. The reduced time [1] contained in the NETAVEM constitutive relations and its dependence on the actual time are determined by the distances from the stress axis to two points corresponding to the same stress value and lying on the graphs for the damaged and undamaged specimens. The relaxation kernel is determined in the experiment with the undamaged specimen. These two material functions and the curve obtained for the damaged specimen are used to obtain the NETAVEM aging function, and then the function of viscosity can be calculated. As a result, all characteristics of the damaged material become known, and the strength of structures made of this material can be calculated.     

Atomic Force Microscopy Measurement of the Resistivity of Semiconductors

Technical Physics - The surface of silicon substrates has been studied experimentally and theoretically by the method of atomic force microscopy spreading resistance imaging, and measuring...     

Two points of view on photon: Quantum field theory and photocounts

Modern concepts of the physical phenomenon described by the term “photon”, which was introduced simultaneously with the acceptance of quantum concepts in physics, are presented. Since that time, this term is a necessary component of each discussion about the physical meaning of quantum mechanics. These discussions are generally carried out within the concepts that are 50 or even 100 years old. At the same time, new fields of science have arisen and been developed in the last century: quantum mechanics and quantum electrodynamics, nonlinear optics, theory of dynamic chaos, etc. The experimental potential has been significantly increased, especially when highly coherent lasers were developed. As a result, the difficult problems of quantum mechanics have become aggravated and enriched. In this paper, we discuss two different approaches to gaining insight into the photon nature, which differ radically. An especially urgent problem is the difference in the estimates of the length of light states that are put into correspondence with photons: laser photons are many orders of magnitude longer than the photons put into correspondence with photocounts. Correspondingly, the spectrum of photocounts is many orders of magnitude wider than the lasing spectrum. The author believes that a photocount cannot be put into correspondence with a photon, because the former is a manifestation of the Coulomb nonlinearity of photodetector. The final solution of the question of the photon nature is expected to be obtained experimentally.     

Nonlinear magnetotransport in a two-dimensional electron system with anisotropic mobility

Nonlinear magnetotransport of two-dimensional electrons in modulation-doped GaAs/AlAs heterostructures with anisotropic mobility is investigated. The mobility attains its maximum and minimum values in the $\left[ {1\bar 10} \right]$ and [110] directions, respectively. It is found that, upon an increase in the direct electrical current I _dc though Hall bars oriented along the [110] direction, the transition of the two-dimensional system to the state with differential resistance r _xx ≈ 0 in a magnetic field occurs at a lower value of I _dc and is accompanied by a more pronounced “plunge” into the region of negative r _xx values as compared to bars oriented along the $\left[ {1\bar 10} \right]$ direction. The results are explained by the impact of mobility on the spectral diffusion of nonequilibrium charge carriers.     

Nonlinear magnetotransport in a two-dimensional electron system in a square array of antidots in GaAs/AlAs heterostructures

Nonlinear magnetotransport of two-dimensional electrons in square antidot lattices prepared on the basis of selectively doped GaAs/AlAs heterostructures with the period that is much less than the electron mean free path in the initial GaAs quantum wells but is much larger than their Fermi wavelength has been studied. It has been shown that the character of the nonlinear transport of the two-dimensional electrons in the lateral lattices under study changes from classical to quantum with the decrease in the antidot radius. It has been found that the quantum lifetime increases in the magnetic field corresponding to the condition of equality of the cyclotron diameter of two-dimensional electrons and the antidot lattice period.