Microwave photoresistance in a two-dimensional electron system with anisotropic mobility

The effect of microwave radiation on magnetotransport in single GaAs quantum wells with anisotropic mobility, whose maximum corresponds to the direction and minimum to the [110] direction, is investigated using the Van der Pauw method. In samples shaped as squares with sides oriented along the and [110] directions, giant oscillations of magnetoresistance arise under the effect of a microwave field for the both and [110] orientations of the measuring current I _ac. In the anisotropic two-dimensional system under study, the relative amplitude of microwave photoresistance oscillations in a magnetic field weakly depends on the orientation of I _ac. At a temperature of 4.2 K and a microwave frequency of 130 GHz, magnetic field intervals characterized by close-to-zero resistance manifest themselves only for the case of the [110] orientation of I _ac. The aforementioned experimental results are qualitatively explained by a quasi-one-dimensional potential modulation of the two-dimensional electron gas in the [110] direction. Original Russian Text ? A.A. Bykov, D.R. Islamov, A.V. Goran, A.K. Bakarov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 891–895.     

Absolute negative resistance in a nonequilibrium two-dimensional electron system in a strong magnetic field

The effect of microwave electromagnetic radiation on the resistance of the 2D electron gas in a GaAs/AlAs heterostructure in a strong magnetic field is investigated. It is shown that, under the nonequilibrium conditions caused by microwave radiation, the aforementioned 2D system exhibits giant oscillations of its resistance with varying magnetic field. When the measuring current density is small, an increase in the microwave power leads to the appearance of an absolute negative resistance at the main minimum of these oscillations, which lies near the cyclotron resonance. The experimental data are found to be in qualitative agreement with the theory of multiphoton photoinduced impurity scattering [J. Inarrea and G. Platero, Appl. Phys. Lett. 89, 052109 (2006)].     

Influence of external nonuniform magnetic field on the spectral characteristics of a virtual cathode oscillator’s output radiation

The influence of an external non-uniform magnetic field created using a periodic magnetic focusing system on the spectral characteristics of a virtual cathode oscillator’s output radiation is investigated by means of numerical simulation. It is shown that raising the magnetization intensity of a single magnetic ring or the number of magnetic rings leads to an increase in the output microwave radiation power spectrum’s irregularity. As consequence, the output microwave signal exhibits wide-band oscillations with a bandwidth close to one octave.     

Giant magnetoresistance oscillations induced by microwave radiation and a zero-resistance state in a 2D electron system with a moderate mobility

The effect of a microwave field in the frequency range from 54 to 140 GHz on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than 10⁶ cm²/V s is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in the magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-GHz microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than 10⁶ cm²/V s does not prevent the formation of zero-resistance states in a magnetic field in a two-dimensional system under the effect of microwave radiation.     

On the source of auroral kilometric radiation

The radiation pattern has been determined on the basis of the comparative analysis of auroral kilometric radiation (AKR) received in the space-diversity mode by two satellites, Interball-2 and Polar. The radiation propagates in a cone with an opening angle ∼±25° and the axis aligned with the local magnetic field. The results con-firm the theoretical estimates that the source boundaries play a significant role in the generation of the auroral kilometric radiation and in the formation of the radiation pattern. Original Russian Text ? M.M. Mogilevsky, T.V. Romantsova, J. Hanasz, T.M. Burinskaya, R. Schreiber, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 11, pp. 819–821.     

Proton and light-ion acceleration to relativistic GeV energies by the superstrong laser radiation interacting with a structured plasma target

A new scheme is proposed for proton and light-ion acceleration to relativistic energies by superstrong laser radiation interacting with a structured plasma target. The proposal consists in the use of two-component targets consisting of heavy and light ions, where an ambipolar field is formed under the action of the ponderomotive force of incident radiation, and, in contrast to the traditional schemes, acceleration starts from the front boundary of the layer. It is shown that, for the optimized target parameters, monoenergetic GeV ion beams can be produced for radiation pulse intensities on the order of 10²¹−10²² W/cm². Original Russian Text ? A.V. Korzhimanov, A.A. Gonoskov, A.V. Kim, A.M. Sergeev, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 9, pp. 662–669.     

Alfvén waves in the electron-nuclear plasma in the peripheral crust of a neutron star as a residual effect of a supernova explosion

The conservation of magnetic flux in the evolution and collapse of massive stars suggests that Alfvén magnetoplasma oscillations can be excited in an isolated neutron star by residual (after the supernova explosion) disturbances of the magnetized electron-nuclear plasma localized in the peripheral crust of the star. The frequencies of the poloidal Alfvén oscillations are calculated in the uniform magnetic field approximation, and it is found that the periods of the oscillations fall into the time interval of the periodicity of radio pulsar radiation. This coincidence of the periods could mean that, at least for some pulsars observed in the radio range, the electromagnetic activity is due to converstion of the energy of magnetoplasma oscillations into electromagnetic radiation. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 593–598 (10 November 1996)     

Quantum waves in noble metals

A theoretical study is presented of the effect of hole energy quantization in a dc magnetic field on microwave penetration through a noble-metal plate. It is shown that quantization results in strong oscillations of cyclotron absorption. Between the absorption peaks, the damping decreases sufficiently to enable propagation of unique quantum waves. Excitation of such waves in a metallic plate gives rise to sharp oscillations of its surface resistance with magnetic field. The shape of these oscillations is also very unusual. Fiz. Tverd. Tela (St. Petersburg) 41, 1354–1360 (August 1999)     

Nonlinear effects in a two-dimensional electron gas with a periodic lattice of scatterers

The magnetoresistance of two-dimensional (2D) electrons in a periodic lattice of antidots is found to be substantially influenced by an applied electric field. The non-Ohmic behavior of the resistance in the region of commensurability oscillations originates from the electric-field-induced breakdown of the trajectories skipping along the lattice arrays. In the region of magnetic fields where the cyclotron diameter is less than the distance between antidots the breakdown of the orbits skipping around antidots is responsible for the nonlinear behavior of the magnetoresistance. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 237–241 (10 February 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Magnetorotational instability in a nonuniform magnetic field

It is shown that the characteristics of the magnetorotational instability noticeably change in the presence of the inhomogeneity of a magnetic field in which rotation occurs. A decrease in the magnetic field with an increase in the distance from the rotation center, which is typical for astrophysical objects, can lead to a significant decrease in the threshold velocity of the object medium rotation, as well as to mitigation of the requirements on a rotation velocity profile that are necessary for the development of instability. Other examples that demonstrate the indicated effects are given. Original Russian Text ? V.I. Ilgisonis, I.V. Khalzov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 11, pp. 815–818.     

Charge ordering in crystals of Pr1? x Sr x MnO3 ( x = 0.22, 0.24) ferromagnetic manganites

The structural and magnetic states of Pr_1−x Sr _x MnO₃ (x = 0.22, 0.24) manganite crystals were studied over a wide temperature range. Measurements of the magnetic susceptibility and electrical resistivity demonstrated that these manganites belong to the class of ferromagnetic semiconductors. Thermal neutron elastic scattering patterns revealed that, in the temperature range 4.2–350 K, the manganites have an orthorhombic structure (space group Pnma) with a well-pronounced cooperative Jahn-Teller effect. Major emphasis was placed on the nuclear magnetic superstructure with a wave vector q = (2π/2a, 0, 2π/2c). It was shown that this superstructure suggests 1/4-type charge ordering in the manganites under investigation. Original Russian Text ? S.F. Dubinin, S.G. Teploukhov, V.E. Arkhipov, V.D. Parkhomenko, é.A. Neĭfel’d, A.V. Korolev, N.A. Ugryumova, Ya.M. Mukovskiĭ, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 704–710.     

Anomalous hall effect in HoB12

Within a wide temperature range of 1.8–300 K, the Hall effect in holmium dodecaboride is investigated. The measurements of the angular dependences of the Hall resistance ρ_H(φ, T, H) for HoB₁₂ performed in a high magnetic field up to 80 kOe at helium and intermediate temperatures made it possible to separate the normal and anomalous contributions to the Hall effect. Analysis of the anomalous component behavior in the paramagnetic and Néel phases suggests the appearance of the 5d-state magnetic polarization (the spin polaron effect) and makes it possible to compare the revealed features of the Hall coefficient R _H(T, H) with the H-T magnetic phase diagram of HoB₁₂. Original Russian Text ? N.E. Sluchanko, D.N. Sluchanko, V.V. Glushkov, S.V. Demishev, N.A. Samarin, N.Yu. Shitsevalova, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 9, pp. 691–694.     

Stimulated radiation pressure acting on an atom nonadiabatically interacting with the field of counterpropagating frequency-modulated waves

The stimulated radiation pressure acting on an atom nonadiabatically interacting with the field of counterpropagating frequency-modulated waves is shown to reach high values typical for the rapid adiabatic passage of the instantaneous frequency of the field of the counterpropagating waves through resonance with an atomic transition. Under the appropriate choice of interaction parameters, the radiation pressure changes insignificantly in a wide range of atomic velocities. Original Russian Text ? V.I. Romanenko, L.P. Yatsenko, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 868–872.     

Hall resistance anomalies induced by a radiation field

A study is made of the four-terminal Hall junction under the influence of a radiation field. The frequency of the radiation field is tuned to a transition between the energy of a bound state below a conduction subband and the Fermi energy of the incident electrons. Radiation-field-induced resonant dips of the Hall resistance are exhibited at low magnetic fields. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 403–408 (25 September 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Excitation of plasma oscillations during the motion of Josephson vortices in layered superconductors

The electric and magnetic fields arising during uniform motion of a vortex lattice in a magnetic field oriented parallel to the conducting layers are calculated in an exactly solvable model. For low temperatures and high velocities of the lattice, features due to the excitation of plasma oscillations of the superconducting electrons appear in the current-voltage characteristic. Peaks associated with plasmon excitation and the Cherenkov effect are present in the radiation spectrum. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 811–816 (25 December 1997)     

Synchronization of high-frequency vibrations of slipping phase centers in a tin whisker under microwave radiation

Current-voltage characteristics of a system with a variable number of slipping phase centers resulting from phase separation in a tin whisker under external microwave field with a frequency Ω/2π≅35–45 GHz have been studied experimentally. Emergence and disappearance of steps with zero slope in a whisker’s current-voltage characteristic at U _m/n =(m/n)U _Ω, where m and n are integers and U _Ω is determined by Josephson’s formula _ℏΩ=2eU _Ω, have been investigated. Microwave field generated by slipping phase centers is nonharmonic, and the system of slipping phase centers permits synchronization of internal oscillations at a microwave frequency by an external field with a frequency which is the n-th harmonic of internal oscillations. The estimated microwave power generated by a whisker is 10⁻⁸ W. Stimulation of superconductivity in a current-carrying whisker has been detected. Zh. éksp. Teor. Fiz. 113, 1364–1375 (April 1998)     

Experimental observation of cyclotron superradiance

Intense (several hundreds of kilowatts) subnanosecond coherent microwave radiation — cyclotron superradiance of an electron swarm moving in a uniform magnetic field — was recorded. The maximum power of the radiation was observed under group synchronization conditions, when the translational velocity of the swarm is equal to the group velocity of the waves in the waveguide channel. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 322–325 (10 March 1996)     

Magnetic moment of a quasi-one-dimensional nanostructure in an inclined magnetic field

Shubnikov-de Haas oscillations in quasi-one-dimensional nanostructures (carbon nanotubes and quantum channels) are investigated. It is shown that two types of aperiodic oscillations arise in such systems: oscillations involving a change in the strength of the magnetic field, and oscillations involving a change in the angle of inclination of the field with respect to the symmetry axis of the system. It is found that the monotonic part of the magnetic moment lies in the plane of size confinement of the system and that the oscillating part has both longitudinal and transverse components. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 549–552 (10 April 1996)     

Observation of resistance oscillations in small-area superconducting aluminum films

In simply-connected, micron-size, aluminum thin-film structures in a perpendicular magnetic field, resistance oscillations with a period close to the quantum of magnetic flux through the area of the structure are observed. The results obtained attest to the fact that when Abrikosov vortices penetrate into a small-area superconducting film (mesoscopic superconducting film), the film behaves similarly to a Little-Parks thin-film interferometer. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 555–558 (25 October 1996)