Table of contents

Recent studies of two-band superconductors using the Ginzburg–Landau (GL) theory are reviewed. The upper and lower critical fields [H_c2(T) and H_c1(T), respectively], thermodynamic magnetic field H_cm(T), critical current density j_c(T), magnetization M(T) near the upper critical field, and the upper critical field H_c2^film(T) of thin films are examined from the viewpoint of their temperature dependence at a point T_c using the two-band GL theory. The results are shown to be in good agreement with the experimental data for the bulky samples of superconducting magnesium diboride, MgB₂, and nonmagnetic borocarbides LuNi₂B₂C and YNi₂B₂C. The specific heat jump turns out to be smaller than that calculated by single-band GL theory. The upper critical field of thin films of two-band superconductors is calculated and the Little–Parks effect is analyzed. It is shown that magnetic flux quantization and the relationship between the surface critical magnetic field H_c3(T) and the upper critical field H_c2(T) are the same as in the single-band GL theory. Extension of the two-band GL theory to the case of layered anisotropy is presented. The anisotropy parameter of the upper critical field H_c2 and the London penetration depth λ, calculated for MgB₂ single crystals, are in good agreement with the experimental data and show opposite temperature behavior to that in single-band GL theory.

The responses of the existing underground detectors to neutrino bursts from collapsing stars evolving in accordance with various models are considered. The interpretation of the results of detecting neutrino radiation from the SN1987A supernova explosion is discussed. A combination of large scintillation counters interlayered with iron slabs (as a target for the electron neutrino interaction) is suggested as a detector for core collapse neutrinos. Bounds for the galactic rate of core collapses based on 28 years of observations by neutrino telescopes of RAS INR, LSD, and LVD detectors are presented.

Negative refraction occurs at interfaces as a natural consequence of the negative group velocity of waves in one of the interfacing media. The historical origin of this understanding of the phenomenon is briefly discussed. We consider several physical systems that may exhibit normal electromagnetic waves (polaritons) with negative group velocity at optical frequencies. These systems are analyzed in a unified way provided by the spatial dispersion framework. The framework utilizes the notion of the generalized dielectric tensor ε_ij(ω, k) representing the electromagnetic response of the medium to perturbations of frequency ω and wave vector k. Polaritons with negative group velocity can exist in media (whether in natural or in artificial meta-materials) with a sufficiently strong spatial dispersion. Our examples include both gyrotropic and nongyrotropic systems, and bulk and surface polariton waves. We also discuss the relation between the spatial dispersion approach and the more familiar, but more restricted, description involving the dielectric permittivity ε(ω) and the magnetic permeability μ(ω) .

The feasibility of applying the similarity law to different types of pulsed discharges is analyzed. The analysis is based on the dependence pτ = f(E/p), where τ is the charge formation time, p is the gas pressure, and E is the pulsed field strength at which the breakdown occurs. The law holds for the Townsend and streamer breakdowns for a relatively long discharge gap d (for atmospheric air, d > 1 cm). For millimeter gaps, this law applies to many gases only in the case of the multielectron breakdown initiation down to the picosecond range. In this case, the time τ is measured from the instant the voltage amplitude sets in to the onset of current buildup and of the drop in voltage across the gap during the simultaneous development of a large number of electron avalanches. In the initiation by a small number of electrons, the time τ is longer than in the multielectron initiation by nearly an order of magnitude; this is due to the relatively low rate of free-electron accumulation in the gap, with runaway electrons (REs) playing an important role in this process. But the time θ of the fast voltage drop and current buildup obeys the similarity law pθ = F(E/p) in both cases. It is hypothesized that the source of REs is the field emission from cathodic micropoints, which terminates at the onset of explosive electron emission to limit the RE current pulse duration to 10⁻¹⁰ s. The similarity law pτ = f(E/p) is shown to hold for a pulsed microwave breakdown.

A critical review of experimental studies on so-called 'slow light' arising due to the anomalously high steepness of the refractive index dispersion under conditions of electromagnetically induced transparency or coherent population oscillations is presented. It is shown that a considerable amount of experimental evidence of the observation of 'slow light' is not related to the low group velocity of light and can be easily interpreted in terms of a standard model of interaction of light with a saturable absorber.

The observable world is the one consisting of nucleons and electrons. The mass of the nucleon arises from chiral symmetry breaking in quantum chromodynamics (QCD), so that high-energy accelerator experiments cannot give any clues to the nature of the mass of matter in the observable world. The origin of the mass of matter will be clarified when the mechanism of chiral symmetry breaking in QCD will be established.

A scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS) was held in the Conference Hall of the P N Lebedev Physics Institute, RAS on 19 April 2006. The following reports were presented at the session:

(1) Kagan M Yu, Klaptsov A V, Brodsky I V (P L Kapitza Institute for Physical Problems, RAS, Moscow), Combescot R, Leyronas X (Ecole Normale Supériure, Paris, France) "Composite fermions and bosons in ultracold gases and in high-temperature superconductors"; (2) Andriyash A V, Loboda P A, Lykov V A, Politov V Yu, Chizhkov M N (Russian Federal Nuclear Center 'E I Zababakhin All-Russian Research Institute of Technical Physics', Snezhinsk, Chelyabinsk region) "Lasers and high energy density physics at the All-Russian Research Institute of Technical Physics"; (3) Murtazaev A K (Institute of Physics, Dagestan Scientific Center, RAS, Makhachkala) "Monte Carlo studies of critical phenomena in spin lattice systems"; (4) Cherepenin V A (Institute of Radioengineering and Electronics, RAS, Moscow) "Relativistic multiwave oscillators and their possible applications".

An abridge version of the reports is given below. • Composite fermions and bosons in ultracold gases and in high-temperature superconductors, M Yu Kagan, A V Klaptsov, I V Brodsky, R Combescot, X Leyronas Physics-Uspekhi, 2006, Volume 49, Number 10, • Lasers and high energy density physics at the All-Russian Research Institute of Technical Physics (VNIITF), A V Andriyash, P A Loboda, V A Lykov, V Yu Politov, M N Chizhkov Physics-Uspekhi, 2006, Volume 49, Number 10, • Monte Carlo studies of critical phenomena in spin lattice systems, A K Murtazaev Physics-Uspekhi, 2006, Volume 49, Number 10, • Relativistic multiwave oscillators and their possible applications, V A Cherepenin Physics-Uspekhi, 2006, Volume 49, Number 10,