卷 104, 编号 7 (2016)

We theoretically study how magnetic modulation can be used to manipulate the transport properties of heterostructures formed by a thin film of a three-dimensional topological insulator sandwiched between slabs of a normal insulator. Employing the k ∙ p scheme, in the framework of a continual approach, we argue that electron states of the system are spin-polarized when ultrathin magnetic insertions are incorporated into the film. We demonstrate that (i) the spin-polarization magnitude depends strongly on the magnetic insertion position in the film and (ii) there is the optimal insertion position to realize quantum anomalous Hall effect, which is a function of the material parameters, the film thickness and the topological insulator/normal insulator interface potential. For the heterostructure with a pair of symmetrically placed magnetic insertions, we calculate a phase diagram that shows a series of transitions between distinct quantum regimes of transverse conductivity. We provide consistent interpretation of recent experimental findings in the context of our results.

Raman and Mössbauer spectra from ¹¹⁹Sn nuclei in CaSnO₃ perovskite have been studied at high pressures up to 75 GPa. A linear increase in the frequency of the main Raman modes and a monotonic decrease in the isomer shift in Mössbauer spectra in the pressure range of 0–40 GPa are established. It is shown that the pressure-induced increase in Raman frequencies can be associated with the variation of the angle between the Sn–O–Sn bonds in chains of oxygen octahedra SnO₆ along the c axis. The sharp variation of the parameters of the Raman and Mössbauer spectra is observed in the pressure region of 40–55 GPa, indicating the structural phase transformations, which can be associated with the transition into the post-perovskite state. Raman spectra of CaSnO₃ samples with the ilmenite structure have been obtained for the first time.

The photoconductive gain, hole photocurrent spectra in the mid-infrared range, and band-to-band photoluminescence spectra in arrays of Ge/Si quantum dots with different elemental compositions of the heterointerface are measured. The diffusive mixing of the materials of the matrix and the dots is controlled by varying the temperature at which the Ge layers are overgrown with Si. It is found that the formation of abrupt heterointerfaces leads to the enhancement of the hole photocurrent and quenching of photoluminescence. The results are explained by an increase in the lifetime of nonequilibrium holes owing to the suppression of their capture into the bound states of quantum dots.

We predict that the propagation of the third sound in a film is accompanied by the emergence of the electric field in the surrounding space, which can be observed by modern methods. It has been shown that the influence of thermally activated vortices on this effect is weak even near the superfluid transition.

We provide a review of the experimental and theoretical research in the field of quantum tomography with an emphasis on recently developed adaptive protocols. Several statistical frameworks for adaptive experimental design are discussed. We argue in favor of the Bayesian approach, highlighting both its advantages for a statistical reconstruction of unknown quantum states and processes, and utility for adaptive experimental design. The discussion is supported by an analysis of several recent experimental implementations and numerical recipes.

The self-dual solution to lattice Euclidean gravity is constructed. In contrast to the well-known Eguchi–Hanson solution to continuous Euclidean Gravity, the lattice solution is asymptotically globally Euclidean, i.e., the boundary of the space as r → ∞ is S³ = SU(2)

Optical second harmonic generation at the photon energy of 2ℏω = 2eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses (0.4–2.5 THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse arises through the electric dipole mechanism of the interaction of the electric field of a pump pulse with the electron subsystem of NiO. Temporal changes in optical second harmonic generation during 7 ps after the action of the pulse are also of an electric dipole origin and are determined by the effects of propagation of the terahertz pulse in a NiO platelet. Coherent oscillations of spins at the antiferromagnetic resonance frequency induced by the magnetic component of the terahertz pulse induce a relatively weak modulation of magnetic dipole optical second harmonic generation.

A formula for the contribution ΔG^res(T) to the resonant tunneling conductance of the N–I–N junction (where N is a normal metal and I is an insulator) with a weak (low impurity concentrations) structural disorder in the I layer from the low-temperature “smearing” electron Fermi surfaces in its N shores is obtained. It is shown that the temperature dependence ΔG^res(T) in such a “dirty” junction qualitatively differs from the corresponding dependence ΔG₀(T) in a “pure” (without resonant impurities in the I layer) junction: ΔG^res(T) < 0, d(ΔG^res)/dT < 0; ΔG₀(T) > 0, d(ΔG₀)/dT > 0, which can serve as an experimental test of the presence of impurity tunneling resonances in the disordered I layer.