Alexander M. Gabovich

We studied the influence of interlayer spacing on the nanoscale electronic states of layered nitride chloride superconductors α-MxTiNCl (M = pyridine (Py), Na, K) using scanning tunneling microscopy and spectroscopy. It was shown that these materials exhibit a strong decrease in the critical temperature (Tc) with increasing interlayer spacing d. Our measurements revealed gap-like features in differential conductance spectra that remain nearly independent of Tc and d. The extracted characteristic gap energy Eg shows spatial inhomogeneity on nanometer scales and does not follow the conventional Bardeen–Cooper–Schrieffer scaling. These observations suggest that the detected gap-like feature is more consistent with pseudogap-like behavior, most probably related to other electronic properties, than with true superconducting pairing. It is similar to the situation in cuprate high-temperature superconductors, where pseudogap is a prominent feature. The results suggest the importance of the local electronic structure and doping effects in determining superconducting properties of layered systems.

The problem of the so-called wave-particle duality in quantum mechanics is studied from the scientific and historical viewpoints. The evidence is given that quantum electrodynamics unambiguously dictates the field nature of matter at the micro-level rather than the particle-like structure. The “elementary particles” are wave-like disturbances (quanta) of the corresponding fields. The usage of the term “Cooper pairs” in superconductivity is analyzed and its limits are indicated. It is asserted that the Faraday–Einstein field concept is the true basis of all phenomena observed in the physical vacuum and the condensed media so that the alleged duality is simply a tribute to tradition. The comprehensive analysis carried out in the review was needed, although the author’s position is not new and was explicitly or implicitly expressed earlier by a number of leading scientists working in various branches of physics. Nevertheless, the conceptual failure of the obsolete duality is still not accepted in textbooks and popularizations making this situation detrimental to both education and research.

The influence of a plane interface between two semi-infinite dielectrically dissimilar insulators on the interaction of two point charges located near it has been analyzed. It was shown that their interaction is significantly modified by the polarization charges induced at the interface. In particular, if the charges are in the same medium, then the dependence of their interaction energy W on the distance D between the charges differs from the Coulomb law. At the same time, if the charges are in different media, the interaction law remains Coulombic, but with an effective dielectric constant value. Deviations from the Coulombic interaction were calculated quantitatively and investigated analytically. The maps W(Rs, Rp) describing the profiles of W as a function of the charges' coordinates Rs and Rp are presented. The approximations of W(D) were obtained and their validity was analyzed. It was concluded that in layered structures, polarization corrections should always be taken into account when studying various properties of charged entities, e.g., electrons and holes forming Wannier-Mott excitons.

Surfaces of some metals (copper and aluminum) and alloys (black and chromium–nickel stainless steels) were irradiated with argon ion-plasma flows under the trampoline mode conditions, i.e., at high ion current densities j≥10mAcm−2 and relatively low ion kinetic energies E=(50−200)eV, which brought about a formation of two-scale (micro-nano) hierarchical rough structures on the sample surfaces. In other experiments, black steel was preliminarily processed in the trampoline regime, and nano-clusters of stainless steel were deposited from an additional target mounted inside the same chamber. The deposited coatings reproduced the composition of the multi-component sputtered target. Strong adhesion between the coating and the sample was obtained, which was proved by dynamic micro-hardness measurements. A high quality of surface patterns created in the trampoline regime was ensured by the release of ion energy near the sample surface and the formation in the quasi-liquid state of a micro-nano-scale structure of the metal upper near-surface layers. Wettability measurements demonstrated that the freshly prepared textured surfaces were hydrophilic, whereas after tens-of-minutes exposures in the ambient atmosphere, they became hydrophobic. The dependence of the textures on the incidence angle θ was measured. It was shown that the increase of θ induces the expansion of micro-nano-scale formations on the surface. Theoretical calculations using the kinetic Monte Carlo approach and simulating the driving force of surface structuring (in our case, this is ion irradiation) were applied to analyze numerically the formation of hierarchical micro-nano-structures at the initial stage of surface modification when the seed inhomogeneities appear and evolve. The results qualitatively correlate with the experimental observations.

The temperature dependences of both the maximum Josephson current IJc and the gap value Δ of the superconducting Bi-based cuprate PbxBi2–xSr2Ca2Cu3O10 + y (PbBi2223) were investigated by using the break junction (BJ) technique that can form superconductor–insulator–superconductor structures. The Josephson current IJc completely disappeared at the resistively determined critical temperature Tc, while the gap Δ did not disappear at Tc and continuously decreased with T above this point. The value of the IJcRN product (RN is the normal resistance outside the gap) at T = 4.2 K is in the range of 4∼24 mV, showing significantly different magnitudes. The T dependences of IJcRN product for junctions possessing various tunnel barrier properties demonstrate non-monotonic decrease with increasing T, which does not agree with the conventional Bardeen–Cooper–Schrieffer-like (BCS-like) behavior if one assumes the s-wave symmetry of the order parameter. (In the case of the d-wave order parameter, the situation should be much more involved.) The observed gap values were Δ = 30∼40 meV, so the calculated value IJcRN(AB) = (π/2)Δ/e intrinsic to the Ambegaokar–Baratoff (AB) theory for the s-wave BCS order parameter should be IJcRN(AB) = 50∼65 mV. Those values are much larger than our observed IJcRN values, constituting 1/3∼1/10 of the expected AB value. The observed relatively small magnitudes, large spread, and the non-monotonic T-decrease of the IJcRN may testify to some kind of asymmetric d-wave order parameter with the varying angles of the microcrystal facets in the BJ.

The current situation in high-Tc superconductivity of the hydrides H3S, LaH10, and related compounds has been considered from a methodological viewpoint. Both the physical theoretical and historical backgrounds have been presented and analyzed. The necessity of procedural purity in theory and the compliance with experimental protocol has been discussed. It has been shown that it is too early now to fully recognize the sensational results on hydride superconductivity.

By irradiating the (111) surface of single-crystalline silicon wafers with Ar+ ions in the trampoline mode (high-density flows of low-energy ions) and with the assistance of metal initiator atoms, a transition of those wafers into the “black silicon” optical state was stimulated. This state is characterized by low values of light reflectance (less than 2%) from the irradiated wafer side in a spectral interval from 400 to 1000 nm. Scanning electron microscopy studies showed that this is a result of the emergence of a hierarchical submicron/nanoscale structure at the treated surface of the wafers. This transition can be performed only with the assistance of metal initiator atoms simultaneously evaporated from an auxiliary target in the operating chamber. At the same time, the application of metals initiators affects the effective lifetime of the minority charge carriers in the black state silicon, which is crucial for the efficiency of black silicon application in solar cells. Among the examined metals initiators (Al, Cr, Fe, Ni, Mo, and Cu), only the application of copper made it possible to preserve or even increase the value of this parameter. The electrostatic interaction between free electric charges and dipoles (playing the role of excitons in this case) near the interface in a two-layer system was considered theoretically. It was shown how the system parameters affect the preferable location of excitons and their orientation, which can be applied, e.g., to govern the solar cell efficiency. The formation of black silicon in the trampoline mode is environmentally friendly at all production stages.

A short historical review of the development of tunneling concept in low-temperature condensed matter physics, physical electronics, nuclear physics, chemistry, and biology is given. It is shown how the preceding classical physics is related to the quantum mechanical tunneling phenomenon. The emphasis is placed on the common features of various tunneling manifestations in nature. The triumph of the Faraday–Maxwell–Einstein idea of the physical field has been demonstrated.