Role of surface phenomena in the magnetoresistivity of polycrystalline manganites La1−x CaxMnO3

The dc electrical resistivity and magnetoresistivity of polycrystalline manganites La_1−x Ca_xMnO₃ (x=0–0.3) are investigated as functions of the temperature, magnetic field and electric field, along with the microwave surface resistance. The investigations show that the dc electrical resistivity and magnetoresistivity are governed by the surface properties of the intergranular boundaries. The dc electrical resistivity is observed to decrease substantially (tenfold) for a comparatively small electric field (E⋟100 V/cm). Estimates are obtained for the internal electrical resistivity of the granules, the thickness of the contact layer (which depends on the temperature and the magnetic field), and the height of the potential barrier between the interfaces separating the surface layer and inner layer of a granule. Fiz. Tverd. Tela (St. Petersburg) 40, 1881–1884 (October 1998)     

Dielectric relaxation in deuterated triglycine sulfate crystals

A study has been made of the slow relaxation of the dielectric permittivity of deuterated triglycine sulfate (DTGS) initiated by application of a dc electric field. The field and temperature dependences of the relaxation time associated with domain-wall motion were obtained. The effect of the internal electric field on relaxation processes is seen in different behavior of the field and temperature dependences under different orientations of the external field. The existence in DTGS crystals of two temperature regions of domain-structure rearrangement lying 7–8 and 15–18 °C below the Curie point has been established. Fiz. Tverd. Tela (St. Petersburg) 40, 1542–1545 (August 1998)     

Antipolarization effect in quantum wells in a strong external alternating field

It is shown that when a strong ac electric field acts on an electron in a double quantum well, the dipole moment is an almost periodic function of the dc voltage applied to the structure. An antipolarization effect — the structure is polarized in a direction opposite to the external field — appears during one half of the period. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 6, 386–391 (25 September 1999)     

Criterion for microwave breakdown of gases

An analytical criterion is obtained for microwave breakdown of gases that takes into account the different diffusion coefficients of electrons along and perpendicular to the direction of the electric field. Discharge ignition without electron attachment to the gas molecules and in electronegative gases is examined, along with microwave discharge ignition when a weak dc electric field is applied. Zh. Tekh. Fiz. 69, 25–29 (November 1999)     

Domain Patterns in the Microwave-Induced Zero-Resistance State

It has been proposed that the microwave-induced “zero-resistance” phenomenon, observed in a GaAs two-dimensional electron system at low temperatures in moderate magnetic fields, results from a state with multiple domains, in which a large local electric field E(r) is oriented in different directions. We explore here the questions of what may determine the domain arrangement in a given sample, what do the domains look like in representative cases, and what may be the consequences of domain-wall localization on the macroscopic dc conductance. We consider both effects of sample boundaries and effects of disorder, in a simple model, which has a constant Hall conductivity, and is characterized by a Lyapunov functional.     

On the nature of the influence of an electric current on the magnetically stimulated microplasticity of Al single crystals

A large increase in dislocation mobility in Al single crystals in a static magnetic field in the absence of mechanical loading of the samples is observed when a dc electric current of low density (10⁵–10⁶ A/m²)is additionally passed through the samples. Apparently, the role of the current reduces to depinning of dislocations from strong pinning centers on the surface of the crystal as a result of surface electromigration of defects. This interpretation is supported by the fact that in samples whose surface is insulated by a layer of lacquer the passage of a current through the volume of the crystal does not change the ordinary dislocation mobility level in a magnetic field. It is hypothesized that surface electromigration of defects, which frees dislocations and unblocks dislocation sources, also plays a key role in the physical mechanism of the long-ago discovered macroplastification of metals upon the passage of an electric current through them. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 788–793 (25 May 1998)     

Fast and wide-range continuously tunable Šolc-type filter based on periodically poled LiNbO3

We present a fast and wide-range continuously tunable Šolc-type filter based on periodically poled LiNbO₃ (PPLN) in this paper. The filter is formed in PPLN by applying a biased dc electric field along the y-axis, and the tuning of a transmitted central wavelength is realized by applying another dc electric field along the z-axis. The numerical results demonstrate that the tuning range covers as much as 16 nm, and the dependence of the transmitted central wavelength shift on the control electric field, shows a nearly linear relation with a tuning rate of 0.95 kV/mm per nm. PACS 42.65.-k; 78.20.Jq; 42.79.Ci     

Surface polaritons in a dielectric at a boundary with a metal in a static electric field

The existence of surface polaritons in a dielectric at a boundary with an ideal metal or superconductor in a static electric field is predicted. The frequency regions in which polaritons exist are substantially different for opposite orientations of the electric field, so that a change in the direction of the field signifies “switching on” or “switching off” of surface polaritons with a fixed frequency. Pis'ma Zh. éksp. Teor. Fiz. 68, No. 12, 876–880 (25 December 1998)     

Effect of a magnetic field on thermally activated tunneling ionization of impurity centers in semiconductors

An expression for the probability of thermally activated tunneling ionization in an electric field in the presence of a magnetic field is obtained. It is shown that the logarithm of the ionization probability is proportional to the squared electric field, and the coefficient of proportionality decreases with increasing magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 763–767 (25 November 1998)     

Electron polarization in quantum wells in a strong variable field

The wave function of an electron in a symmetric double quantum well placed in a strong time-periodic electric field is found, expressions for quasienergy functions are derived, and the dependence of the dipole moment on the average electric field is analyzed for the case where the average field remains constant. In the case of slow monotonic variation of the “constant” component of the electric field, the Schro dinger equation is solved by the WKB method. It is found that the dependence of the dipole moment on the average field is of a clearly nonlinear almost-periodic nature and that in the event of adiabatic monotonic variation of the average field there is a periodic relocation of the electron density from well to well with a small frequency proportional to the rate of variation of the average field. Zh. éksp. Teor. Fiz. 116, 217–235 (July 1999)     

Electric-field-enhanced metal-induced crystallization of hydrogenated amorphous silicon at room temperature

A novel simple method of crystallization of hydrogenated amorphous silicon (a-Si:H) thin films is described. Namely, we studied a metal-induced crystallization enhanced by a dc electric field in sandwich p⁺–i–n⁺structures. The samples were fabricated from wide-bandgap a-Si:H with high hydrogen content (13–51 at. % H). Macroscopic islands of a-Si:H (up to ∼1 mm in diameter) in the region between upper (CrNi) and lower (ITO) contacts crystallize instantaneously when a sufficiently high dc electric field (≳10⁵ V cm^-1) is applied. The crystallization sets in at room temperature and ambient atmosphere and is spatially selective. A proposed microscopic mechanism of such an easy macroscopic crystallization consists in easy diffusion of Ni and/or Ni silicides (representing nucleation sites) through a dense network of voids in hydrogen-rich a-Si:H. Received: 30 November 2000 / Accepted: 3 May 2001 / Published online: 27 June 2001     

Many-electron tunneling in atoms

A formula for describing the N-electron ionization of atoms by a dc field and laser radiation in the tunneling regime is derived theoretically, and numerical examples for noble-gas atoms are presented. Zh. éksp. Teor. Fiz. 116, 410–417 (August 1999)     

Coexistence of the relaxor-like and ferroelectric behavior in K1-xLixTaO3

ABSTRACT

The results of low-temperature linear and nonlinear susceptibilities, polarization measurements and the dc electric field dependence of the dielectric properties of the lithium-doped potassium tantalate K_1-xLi_xTaO₃, x = 0.034 (KLT-3.4%Li) solid solution are presented. The coexistence of the relaxor-like and ferroelectric behavior and different mechanisms leading to either of them are discussed. The observed ferroelectric phase transition is of the first-order type with temperature hysteresis. This transition is due to the off-center motions of Ta ions in the octahedral environment of oxygen ions. Clusters of Li⁺ ions produce a relaxor-like behavior and random electric field. This field reduces the depolarization field and allows off-center motions of Ta ions and an appearance of spontaneous polarization.     

Ohm’s law in a chiral plasma

The motion of plasma electrons in a stochastic electromagnetic field is studied in the low-conductivity limit. It is shown that under very general conditions, in the presence of a nonzero average chirality of the small-scale electromagnetic field, the effective current depends on the curl of the applied electric field, j=§ E+§_κcurl E, just as for similar dependences for the electric displacement and magnetic induction vectors in optically active and artificial chiral media. Under certain conditions such an Ohm’s law leads to growth of the magnetic field, the structure of the growth being dependent on the conductivity of the medium. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 268–273 (25 August 1999)     

Differential thermopower of a superlattice in a strong electric field

The effect of an electric field on the differential thermopower α(E) of a one-dimensional superlattice is investigated in the semiclassical approximation. A nonmonotonic temperature dependence of α(0) is established for a degenerate electron gas. It is shown that, in principle, an electric field can be used to control the thermoelectric properties of superlattices. Fiz. Tverd. Tela (St. Petersburg) 41, 1314–1316 (July 1999)     

On the unified nature of the longitudinal and transverse acoustoelectric effects in type-II superconductors

A longitudinal ultrasonic wave should drag the vortex structure of superconductors at an acute angle with respect to the direction of wave propagation. This motion engenders longitudinal and transverse electric fields in the superconductor and, moreover, effects of the “optical rectification” type contribute to the observed longitudinal and transverse electric fields. The effect should be observed in all type-II superconductors above the irreversibility line. Both fields have extrema with respect to temperature and magnetic field. In contrast to the acoustoelectric effect in the normal state, the sign of the induced electric field depends on the external magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 222–227 (10 February 1998)     

Natural ferromagnetic resonance in the disordered alloy Pd2AuFe

A contribution to electromagnetic power losses, additional to the losses due to eddy currents and exhibiting a resonance frequency dependence with the main maximum near 1 GHz, has been observed for the ferromagnetic alloy Pd₂AuFe in the frequency range 0.9 MHz–10 GHz in the absence of an external constant magnetic field. Investigations performed in a dc magnetic field show that this effect is a natural ferromagnetic resonance due to intradomain magnetization precession in the effective magnetic-anisotropy field. Fiz. Tverd. Tela (St. Petersburg) 40, 1900–1904 (October 1998)     

Gain without inversion in a medium of 1/2→1/2 atoms

Amplification of a probe field without inversion in a medium of non-degenerate two-level atoms pumped by a circularly polarized optical field in resonance with a 1/2→1/2 atomic transition in the presence of a dc magnetic field orthogonal to the wave vector of the pump field is demonstrated. It is shown that gain without inversion is possible in strong optical and magnetic fields in the case of a pump with a finite spectral width which can be much greater than the natural width of the excited level. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 364–369 (10 September 1998)     

Deep impurity-center ionization by far-infrared radiation

An analysis is made of the ionization of deep impurity centers by high-intensity far-infrared and submillimeter-wavelength radiation, with photon energies tens of times lower than the impurity ionization energy. Within a broad range of intensities and wavelengths, terahertz electric fields of the exciting radiation act as a dc field. Under these conditions, deep-center ionization can be described as multiphonon-assisted tunneling, in which carrier emission is accompanied by defect tunneling in configuration space and electron tunneling in the electric field. The field dependence of the ionization probability permits one to determine the defect tunneling times and the character of the defect adiabatic potentials. The ionization probability deviates from the field dependence e(E) ∝ exp(E ²/E _c ² ) (where E is the wave field, and E _c is a characteristic field) corresponding to multiphonon-assisted tunneling ionization in relatively low fields, where the defects are ionized through the Poole-Frenkel effect, and in very strong fields, where the ionization is produced by direct tunneling without thermal activation. The effects resulting from the high radiation frequency are considered and it is shown that, at low temperatures, they become dominant. Fiz. Tverd. Tela (St. Petersburg) 39, 1905–1932 (November 1997)