Image states on beryllium surfaces with low indices

Using the self-consistent pseudopotential method, we have calculated the binding energy of the image states for the (0001) , and surfaces of beryllium. It is shown for the (0001) face that there exists a pronounced resonance image state with n=1 and energy −0.95 eV at the point of the surface Brillouin zone. In the surface, which has a wide band gap in the vicinity of the vacuum level, the calculated image state with n=1 at the point has energy −1.2 eV and is a surface state of gap type. For the face in the vicinity of the point band gaps are absent. However, the symmetry of the bulk states near the vacuum level enables the existence of a resonance image state with n=1 and energy −0.6 eV. Fiz. Tverd. Tela (St. Petersburg) 41, 935–940 (June 1999)     

Weak carrier localization on the (10\bar 10) tellurium surface

A theory of weak localization responsible for the negative magnetoresistance effect is developed for quantum wells at the tellurium surface, which retains, in contrast to the surface considered earlier, a trigonal spectrum distortion with opposite signs near the M and P extrema, with the latter playing the part of states with opposite spins. It is shown that as a result of the motion in momentum and spin spaces being correlated the spin relaxation due to this distortion is smaller than that for the (0001) surface. Fiz. Tverd. Tela (St. Petersburg) 39, 1659–1664 (September 1997)     

Anomalous electron emission from lithium niobate and lithium tantalate single crystals

Anomalous electron emission from the surface of LiNbO₃ and LiTaO₃ single crystals excited by soft x radiation has been discovered and is investigated. The absence of anomalous emission from the face of these single crystals is established. The experimental results confirm the theoretical conclusions that the anomalous emission is caused by the presence of a maximum in the distribution of the potential in the near-surface layer. The dependence of the lifetime τ of the anomalous emission on the dielectric constant ɛ of the ferroelectric is calculated. Fiz. Tverd. Tela (St. Petersburg) 39, 679–682 (April 1997)     

Fourier transform of supermeasures

In the note, a Smolyanov-Shavgulidze model of infinite-dimensional superspace H _Λ = Λ₀ H ₀ ⊕ Λ₁ H ₁ corresponding to a Hilbert space H = H ₀ ⊕ H ₁ over a Hilbert superalgebra Λ = Λ₀ ⊕ Λ₁ is considered. Its relation to the Khrennikov superspace is discussed. Moreover, H _Λ is equipped with the structure of Hilbert superspace with an inner superproduct (·, ·)_Λ. The supermeasures are defined as Λ^ℂ (∧H ₁)-valued measures on H ₀ (Λ^ℂ stands for the complexification of Λ). The definition of the Fourier supertransform is similar to the ordinary one, (y) = μ(dz). It turns out that the values of the Fourier supertransform of a supermeasure on the subspace = H ₀ ⊕ Λ₁ H ₁ can be obtained by applying a certain operator to the values of the classical Fourier transform. The main result is the theorem claiming that the Fourier supertransform of supermeasures is isometric on superspaces with zero even part (H ₀ = {0}). As a corollary, we note that the operator of Fourier supertransform is injective. We also give necessary and sufficient conditions for the countable additivity of cylindrical supermeasures in terms of continuity of their Fourier supertransforms (an analog of the Minlos-Sazonov theorem).     

Parity anomaly in a \mathcal{P}\mathcal{T}-symmetric quartic Hamiltonian

In this paper, two independent methods are used to show that the non-Hermitian -symmetric wrong-sign quartic Hamiltonian H = (1/2m)p ² − gx ⁴ is exactly equivalent to the conventional Hermitian Hamiltonian . First, this equivalence is demonstrated by using elementary differential-equation techniques and second, it is demonstrated by using functional-integration methods. As the linear term in the Hermitian Hamiltonian is proportional to ℏ, this term is anomalous; that is, the linear term in the potential has no classical analog. The anomaly is a consequence of the broken parity symmetry of the original non-Hermitian -symmetric Hamiltonian. The anomaly term in remains unchanged if an x ² term is introduced into H. When such a quadratic term is present in H, this Hamiltonian possesses bound states. The corresponding bound states in are a direct physical measure of the anomaly. If there were no anomaly term, there would be no bound states.     

The nature of the {\bar p} metastability in helium

A new interpretation of the nature of the metastable states of antiprotons in helium is proposed. The first step is the formation of an ion ( ), which shall be called “ioncule”. After its decay a neutral “atomcule” ( ) is formed which was observed in the experiments on metastable antiprotonic helium. This model explains the experiments in a natural way, in particular the quenching by atomic and molecular admixtures and the pressure dependence of quenching in pure helium. At high helium densities the ioncule creates a vacuum bubble in helium. It is shown that the annihilation of slowed-down can be suppressed at helium pressures of ∼ 10 000 bar. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chains of twists and induced deformations

Chains of extended twists are composed of factors . The set of Jordanian twists { } can be applied to the initial Hopf algebra . In this case the remaining (transformed) factors of the chain can serve as extensions for such a multijordanian twist. We study the properties of these generalized extensions and the spectra of deformations of the corresponding Heisenberg-like algebras. The results are explicitly demonstrated for the case when .     

YBa2Cu3O7−δ /CeO2 heterostructures on sapphire R-plane

(001)YBa₂Cu₃O_7−δ epitaxial films were prepared by laser ablation on surface. A thin (001)CeO₂ or (111)CeO₂ buffer layer was deposited between the substrate and the superconductor film to reduce their chemical interaction. In the initial stages of CeO₂ buffer formation, its orientation depended strongly on the intensity of cerium ion interaction with oxygen. Epitaxial growth of (001)YBa₂Cu₃O_7−δ films was achieved both on and . The T _c temperature of epitaxial (001)YBa₂Cu₃O_7−δ films was within 88–90 K, and the current J _c at 77 K was in excess of 10⁶ A/cm⁻². Fiz. Tverd. Tela (St. Petersburg) 40, 205–208 (February 1998)     

A study of the nuclear-medium influence on neutral-strange-particle production in deep-inelastic neutrino scattering

The influence of nuclear effects on the production of neutral strange particles (V ⁰) is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E _v =3−30 GeV) at the Serpukhov accelerator. The mean multiplicity of V ⁰ particles in nuclear interactions, , is found to exceed significantly that in “quasideuteron” interactions, . The ratio of is larger than that for π⁻ mesons, . It is shown that the multiplicity gain of V ⁰ particles can be explained by intranuclear interactions of produced pions. The text was submitted by the authors in English.     

Orthogonality theorem for a one-dimensional-electron gas with a bounded spectrum

The overlap between the ground-state wave functions of a one-dimensional electron gas with the Hamiltonians Ĥ ₀ and , where is the impurity potential, is calculated. It is shown that in the limit of an infinite potential the overlap vanishes as M ^−1/8 as M→∞, where M is the number of filled levels, while in the case of a weak potential this overlap differs little from 1. A relation is found between the magnitude of the overlap and the behavior of the density of states near the Fermi energy (statistics of the levels). The possibility of linearization of the spectrum and the possibility of performing a bosonization procedure are discussed in light of the results obtained. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 57–60 (10 July 1996)     

Bounds on neutrino mixing with exotic singlet neutrinos

We examine the effects of mixing induced non-diagonal light-heavy neutrino weak neutral currents on the amplitude for the process (with a=e, μ or τ). By imposing constraint that the amplitude should not exceed the perturbative unitarity limit at high energy , we obtain bounds on light-heavy neutrino mixing parameter sin² where is the mixing angle. In the case of one heavy neutrino (mass mξ) or mass degenerate heavy neutrinos, for Λ=1 TeV, no bound is obtained for mξ<0.50 TeV. However, sin² ≤3.8 × 10⁻⁶ for mξ=5 TeV and sin ≤6.0 × 10⁻⁸ for mξ=10 TeV. For Λ=∞, no constraint is obtained for mξ<0.99 TeV and sin² ≤3.8 × 10⁻² (for mξ=5 TeV) and sin² ≤9.6 × 10⁻³ (for mξ=10 TeV).     

Effect of a magnetic field on the yield point of NaCl crystals

A constant magnetic field is found to have a substantial effect on the macroplasticity of NaCl crystals when they are being actively strained at a constant rate during magnetic treatment. We have measured the dependence of the yield point σ _y on the magnetic induction B=0–0.48 T and the strain rate . It is shown that this magnetic effect has a threshold character and is observed only for B>B _c , where B _c grows with increasing as . The lower the strain rate , the larger the relative decrease in the yield point σ _y (B)/σ _y (0) at fixed field B>B _c . At small enough strain rates the threshold field B _c ceases to depend on and goes constant. A theoretical model is proposed which is in good agreement with the observed regularities. The model is based on the competition between thermally activated and magnetically stimulated depinning of dislocations from paramagnetic impurity centers. Zh. éksp. Teor. Fiz. 115, 951–958 (March 1999)     

On the Yangian Y $$(\mathfrak{g}\mathfrak{l}_{m|n} )$$ and its quantum Berezinian

Jonathan Brundan and Alexander Kleshchev recently introduced a new family of presentations for the Yangian Y of the general linear Lie algebra . In this article, we extend some of their ideas to consider the Yangian Y of the Lie superalgebra . In particular, we give a new proof of the result by Nazarov that the quantum Berezinian is central. Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005.     

Thermal expansion anomalies in TbVO4 due to the cooperative Jahn-Teller effect

The thermal expansion anomalies in TbVO₄ due to the cooperative Jahn-Teller effect were studied experimentally and theoretically. Characteristic magnetoelastic anomalies were observed in the curves of Δa/a and Δc/c of the cell parameters at T<T _c. Calculations of the magnetoelastic contribution to Δa/a and Δc/c from fully symmetric and and low-symmetry ɛ^δ modes were performed using the general crystal-field formalism, and the values of the magnetoelastic coefficient B ^δ were obtained from spectroscopic and spontaneous-deformation data. It is shown that the thermal expansion of TbVO₄ in both the tetragonal and orthorhombic phases can be described well on the basis of a general model based on a single set of interaction parameters. Fiz. Tverd. Tela (St. Petersburg) 40, 1663–1666 (September 1998)     

Preferred Invariant Symplectic Connections on Compact Coadjoint Orbits

Let be the Haag--Kastler net generated by the (2) chiral current algebra at level 1. We classify the SL(2, )-covariant subsystems by showing that they are all fixed points nets ^H for some subgroup H of the gauge automorphisms group SO(3) of . Then, using the fact that the net ₁ generated by the (1) chiral current can be regarded as a subsystem of , we classify the subsystems of ₁. In this case, there are two distinct proper subsystems: the one generated by the energy-momentum tensor and the gauge invariant subsystem .     

Pseudodipole interaction of ions with nonzero orbital angular momenta

It is shown that the direct exchange interaction of ions possessing electrons (holes) with orbital angular momenta L and ℓ always contains a contribution , where is a unit vector along the bond connecting the ions. As a result, taking the spin-orbit interaction into account gives rise to a pseudodipole interaction of the spins (total angular momenta) of the ions under study and to uniaxial anisotropy. The possibility of using this pseudodipole interaction to explain the magnetic properties of cuprates is discussed. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 67–72 (10 July 1998)     

Anomalies in the elastic properties of silicious iron single crystals at pressures of up to 9 GPa and the α−ɛ phase transformation

A Fe+5.07 at.%Si single crystal has been studied by ultrasonic-pulse technique. Its density and elastic constants were determined for p=0 and T=293 K. The dependence of the elastic properties of silicious iron on Si concentration was constructed. The compression, the effective elastic constants, and the Grüneisen parameters were measured at hydrostatic pressures of up to 9 GPa. It was found that for p=0, and . The elastic constants c ₄₄ and c′ increase linearly with pressure by 19.3 and 18.2% by p=9 GPa. The elastic anisotropy does not vary with pressure. For p>4 GPa, c ₁₁, c ₁₂, and K _S were observed to increase nonlinearly with decreasing pressure derivative. The Grüneisen parameter γ _LA decreases with pressure down to 0.70 at 9 GPa to become negative when extrapolated to the region of the α−ɛ phase transformation. The anomalies in c ₁₁ and the negative values of γ _LA for p>11 GPa indicate that the phase transformation in silicious iron at 13.5 GPa can take place by the crystallographic mechanism of the α−ɛ transformation in pure iron, i.e. by lattice compression in the [001] direction and shearing of the (110) planes along or . An assumption is put forward that pressure gives rise in silicious iron to sp-d hybridization, which results in increased screening of the ion-ion interaction and in anomalies in elastic properties. Similar phenomena are expected to occur in pure bcc Fe as well. Fiz. Tverd. Tela (St. Petersburg) 41, 516–522 (March 1999)     

Present and future experiments in nonequilibrium reactor antineutrino energy spectrum

Considerable efforts that have been undertaken in recent years in low-energy antineutrino experiments require further systematic investigations in line of reactor antineutrino spectroscopy as a metrological basis of these experiments. We consider some effects associated with the nonequilibrium of reactor radiation and residual emission from spent reactor fuel in contemporary experiments. The text was submitted by the authors in English.