Volume 108, Nº 5 (2018)

Tunneling differential conductivity (or resistivity) is a sensitive tool to experimentally test the non-Fermi liquid behavior of strongly correlated Fermi systems. In the case of common metals the Landau–Fermi liquid theory demonstrates that the differential conductivity is a symmetric function of bias voltage V. This is because the particle–hole symmetry is conserved in the Landau–Fermi liquid state. When a strongly correlated Fermi system turns out to be near the topological fermion condensation quantum phase transition, its Landau–Fermi liquid properties disappear so that the particle–hole symmetry breaks making the differential tunneling conductivity to be asymmetric function of V. This asymmetry can be observed when a strongly correlated metal is in its normal, superconducting or pseudogap states. We show that the asymmetric part of the dynamic conductance does not depend on temperature provided that the metal is in its superconducting or pseudogap states. In normal state, the asymmetric part diminishes at rising temperatures. Under the application of magnetic field the metal transits to the Landau–Fermi liquid state and the differential tunneling conductivity becomes a symmetric function of V. These findings are in good agreement with recent experimental observations.

A modified superexchange model for the formation of nonresonant tunnel current through a molecular wire consisting of a regular chain and terminal units is developed. Under conditions of weak mixing of the localized terminal molecular orbitals with the delocalized orbitals of regular chain, the explicit expressions for the tunneling current are obtained and the conditions for the applicability of the superexchange model are found. It is shown that in limiting cases, the attenuation factor for the tunneling current coincides with that used for analysis of experimental data within the framework of the rectangular barrier model or the “deep” tunneling model. Using the modified superexchange model, the experimental data on the dependence of the currentvoltage characteristics of the N-alkanedithiol molecular wire on the number of C–C bonds are interpreted, and the conditions are formulated for which the simplest model of a rectangular barrier with a tunneling effective electron mass can be used for the analysis of experimental data.

Experimental X-ray absorption spectra near the Fe K edge for as-synthesized MIL-88а metal–organic framework (MIL stands for Materials Institute Lavoisier) before and after activation have been obtained and analyzed for the first time. The theoretical analysis of experimental spectra has revealed changes in the local atomic structure of iron at the desorption of water from pores of the studied material in the process of activation.

The magnetic structure of pseudo-single-crystal (0001) Dy/Gd superlattices, as well as its modification with the temperature, is determined by the combined application of SQUID magnetometry, circular magnetic dichroism, and polarized neutron reflectometry. It is established that a fan magnetic order is formed in the Dy layers in relatively low magnetic fields at temperatures below 170 K. Then, this order propagates coherently throughout the superlattice. The magnetic moments in the Dy layers lie in the basal plane, and in the Gd layers, they are oriented mainly along the hexagonal c axis.

Metamaterials consisting of conducting rings distributed chaotically or periodically in a dielectric matrix, thus forming a photonic crystal, have been considered. Models have been obtained demonstrating that the magnetic response can be both diamagnetic and paramagnetic, but the uniform permeability in a nonresonant region, where it is still meaningful, is close to unity.

Resonant Raman scattering in quantum rings with a sufficiently large number of conduction electrons has been studied. The cross section for Raman scattering accompanied by the excitation of a one-dimensional plasmon in a ring has been determined in the self-consistent field approximation.