Том 108, № 2 (2018)

A hydrodynamic theory of the linear response of a noncollinearly magnetized medium interacting with electromagnetic radiation has been developed. Linear and quadratic magnetization effects caused by the spatial inhomogeneity of the magnetic moment have been analyzed. Linear magnetization effects include an effect similar to nonreciprocal birefringence, as well as reciprocal and nonreciprocal rotation of the plane of polarization, caused by the inhomogeneity of the magnetic moment. It has been shown that an effect caused by the equilibrium spin current can appear in the considered medium. This effect is determined either by the inhomogeneity of the spin current or by the spatial dispersion of a wave. The effect associated with the spatial dispersion of the wave is linear in its wave vector and is similar to nonreciprocal birefringence. The effect associated with the inhomogeneity of the spin current describes the rotation of the plane of polarization, which, however, can occur in the system with zero average magnetization.

It has been shown that the presence of narrowband quantum jumpers in “dirty” (low concentrations of identical nonmagnetic impurities in the insulator (I) layer) S–I–S (S is a superconductor) junctions at the temperature T = 0 significantly reduces the critical supercurrent (Josephson current) as compared to the value given by the known the Ambegaokar–Baratoff relation. The performed estimates have shown the possibility of the experimental manifestation of this effect.

Nonlinear magnetotransport in a two-dimensional electron gas in one-dimensional lateral lattices fabricated from a selectively doped GaAs/AlAs heterostructure is investigated. One-dimensional potential modulation is imposed on the two-dimensional electron gas by means of a set of metal strips formed on the planar surface of Hall bars. The dependences of the differential resistance r_xx on the magnetic field B < 0.5 T are studied at a temperature T = 1.6 K in lattices with a period of a ≈ 200nm. It is shown that periodic oscillations in r_xx(1/B) occur in such lattices under the action of a current-induced Hall field due to Zener tunneling between Landau levels. Interference is found between Zener oscillations and commensurability oscillations of r_xx in two-dimensional electron systems with one-dimensional periodic modulation. The experimental results are qualitatively explained by the role of Landau bands in nonlinear transport at large filling factors.

An explicit expression for the dynamic charge susceptibility for electron-doped cuprates has been derived. This expression accurately reproduces the wave vector dependence of the plasmon frequency observed in inelastic X-ray scattering experiments for Nd_{2 – x}Ce_xCuO₄. The imaginary part of the charge susceptibility along the triangular path in the Brillouin zone is plotted. It is demonstrated that the spectral weight of the plasmon mode near q = 0 is negligibly low. The calculated frequencies of the plasmon mode for all wave vectors in the Brillouin zone turn out to lie outside the range of damping related to electron−hole excitations. A formula for the charge susceptibility is derived within the t−t′−t″−J model supplemented by the Coulomb interaction operator and three-site terms. The derivation is performed by the Green’s function technique employing the formalism of composite Hubbard operators and the Mori projection method, which have proved themselves in the analysis of collective spin excitations. The used Fourier transform of the Coulomb interaction corresponds to the monolayer model with a spatially periodic structure, which is embedded in a three-dimensional crystal lattice.

It has been shown that plasma inhomogeneity reduces the threshold of the parametric instability of two-plasmon decay and, in particular, allows the excitation of plasmons with the same frequency by a spatially uniform pump field.

It has been shown that the rotation of a spherical nanoparticle with the radius R near the surface of a semi-infinite homogeneous medium can result in singular resonance in fluctuation-induced electromagnetic phenomena (Casimir force, Casimir friction, and radiative heat generation). Fluctuation electromagnetic effects increase strongly near this resonance even in the presence of dissipation in the system. The resonance occurs at distances of the particle from the surface d < d₀R(3/4ε″₁(ω₁)ε″₂ (ω₂))^1/3 (where ε″_i(ω_i) is the imaginary part of the dielectric function of the particle or the medium at the frequency of a surface phonon or plasmon polariton ω_i), when the rotation frequency coincides with poles in the photon generation rate at Ω ≈ ω₁ + ω₂. These poles are due to the multiple scattering of electromagnetic waves between the particle and surface under conditions of the anomalous Doppler effect. These poles exist even in the presence of dissipation. At d < d₀, depending on the particle rotation frequency, the Casimir force can change sign; i.e., the attraction of the particle to the surface changes to repulsion. The results can be important for the development of experimental methods for the detection of quantum friction.