Possible weakening of the many-body interactions in the organic quasi-two-dimensional metal α-(BETS)<Subscript>2</Subscript>NH<Subscript>4</Subscript>Hg(SCN)<Subscript>4</Subscript>

The behavior of the de Haas-van Alphen oscillations in the organic quasi-two-dimensional metal α-(BETS)₂NH₄Hg(SCN)₄ is comprehensively studied as a function of the angle between the magnetic-field direction and the normal to the conducting layers in it. The angular dependence of the oscillation amplitude has minima at angles of ±40° and ±62°, which are caused by the spin zero effect. The positions of these minima suggest that the electron-phonon and electron-electron interactions in this metal are significantly weakened.     

Exchange interaction effects in inter-Landau level Auger scattering in a two-dimensional electron gas

We consider the influence of spin effects on the inter-Landau level electron-electron scattering rate in a two-dimensional electron gas. Because of exchange spin splitting, the Landau levels are not equidistant. This leads to the suppression of Auger processes and a nonlinear dependence of the lifetime on the concentration of excited electrons even at very low excitation levels. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 574–579 (25 April 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Long-range chemical interaction in solid-state synthesis: The Kirkendall effect and solid-state reactions in Cu/β-CuZn and Cu/Fe/β-CuZn film systems

The results of the experimental investigations of the solid-state reaction of Cu with β brass, which is associated with the Kirkendall, in Cu/β-CuZn and Cu/Fe/β-CuZn film systems are reported. It has been shown that the initiation temperature of the solid-state synthesis of α brass at the Cu/β-CuZn interface is about 200°C. The chemically inert Fe barrier layers 420 and 850 nm in thickness between the Cu and β-CuZn films do not suppress the solid-state synthesis of the α brass, but increase the initiation temperature to about 250°C. This behavior indicates that the chemical interaction between the Cu and Zn atoms through the chemically inert Fe layer is long-range. The X-ray photoelectron investigations reveal the migration of Zn atoms from the β-CuZn layer through the Fe barrier to the Cu layer. The results are interpreted under the assumption that the migration of Zn atoms in the Kirkendall is initiated by the strong chemical interaction between the Cu and Zn atoms in the Cu and β-CuZn layers, which is due to the synthesis of α brass, rather than by the diffusion random walk, as is commonly accepted at present.     

Precession spin relaxation mechanism caused by frequent electron-electron collisions

It is shown that the D’yakonov-Perel’ spin relaxation mechanism in a two-dimensional electron gas is controlled not only by the electron-momentum relaxation that accounts for the electron mobility but also by the electron-electron collisions. The kinetic equation describing the mixing of electron spin in the k space was solved, and the spin relaxation time τ_s caused by frequent electron-electron collisions was determined. The time τ _s was calculated for a nondegenerate electron gas both with and without allowance for the exchange interaction.     

Spin filtering through ballistic nanojunctions, the role of geometry and of spin orbit interaction

We suggest a spin filter scheme using T-stub nanometric crossjunctions patterned in two dimensional electron gases (2DEGs) in the presence of spin orbit interaction (SOI). We compare the effects of SOI arising from vertical confinement of charge carriers in the well, Rashba or α-SOI, with SOI generated by lateral confinement of the wire, β-SOI. We show that β coupling can be more effective in generating a spin polarized current as compared to α-SOI. We also compare the efficiency of the T-stub filter with the one of the X shaped cross junction.     

Alpha decay of the first excited state of the Th-229 nucleus

The α decay of the anomalously low-lying isomeric level 3/2⁺ (3.5±1.0 eV) of the ²²⁹Th nucleus is studied. The lifetime of the isomer with respect to a decay is predicted and the spectrum of the emitted a particles is calculated. It is noted that the complete α spectrum of the isomer and accelerated α decay of ²²⁹Th can be observed by exciting the nuclei with laser radiation. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 319–323 (10 September 1996)     

Spin control of 12B and 12N and the axial charge from their β-ray spin-alignment correlations

The spin manipulation technique by use of the β-NMR is further refined, based on the recent thorough studies of hyperfine interactions of ¹²B and ¹²N in Mg. By using this technique, the alignment correlation terms in the β-ray angular distribution of the A = 12 system are precisely measured, so that the axial charge is singled out to be y = 4.66 ± 0.06 (stat.) ± 0.13 (syst.) which shows clear mesonic enhancement over the impulse value. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diffraction integral for misaligned systems and interference effects of optical arrays

Summary In the present paper, a diffraction integral formula for a misaligned optical system is derived. The interference effects of opticalelement arrays are studied by means of such a formula. The possibility of eliminating interference fringes is discussed. The conclusion is that the interference fringes could be eliminated when the αβγδ condition for arrays is satisfied. The synthetical aberration is simultaneously eliminated. However, in this case, the synthetical image coincides with the individual images. For some special application, the synthetical image does not coincide with the individual images and the αβγδ condition is not fulfilled. But the interference fringes may disappear in some special cases.

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Riassunto La formula di Collins, che esprime il cammino ottico fra un punto del piano oggetto e un punto del piano immagine nel caso di un sistema ottico centrato, è generalizzata al caso di un sistema ottico disallineato. La formula cosí ottenuta è applicata allo studio del fenomeno d’interferenza che ha luogo nel piano della cosiddetta ?immagine sintetica? fra i vari fasci emergenti da una cortina di elementi ottici. Si discutono infine le condizioni in cui non si hanno frange d’interferenza sull’immagine sintetica.

     

A quantum-topological analysis of noncovalent interactions in secondary polyalanine structures

The geometric parameters and relative stability of γ- and β-loop conformers of oligomers based on alanine were determined by the Kohn-Sham method (the B3LYP/6–31+G** approximation). The three-dimensional architecture of the β-folded structure and protein α-helix was reproduced using Kohn-Sham calculations with periodic boundary conditions. The Bader quantum-topological molecular structure theory was used to reveal and quantitatively characterize noncovalent interatomic interactions in the secondary structures of model peptides under consideration. Earlier unnoticed additional noncovalent interactions stabilizing the structures under consideration were revealed. In β-loops, these are C-H⋯O and H⋯H interactions, and, in antiparallel β-folded structures, these are weak C^β-H⋯H-C^β interactions between side chains. Additional weak bonding interaction between C=O groups in position i and H-C^β groups in position i + 3 was revealed for the protein α-helix; this interaction is usually ignored in amino acid folding simulations with the use of classic force fields.     

Properties of the πη,$ \eta{^\prime}$,σ, f0(980) and a0(980) mesons and their relevance for the polarizabilities of the nucleon

The signs and values of the two-photon couplings F _Mγγ of mesons (M) and their couplings g_MNN to the nucleon as entering into the t -channel parts of the difference of the electromagnetic polarizabilities (α - β) and the backward angle spin polarizabilities γ_π are determined. The excellent agreement achieved with the experimental polarizabilities of the proton makes it possible to make reliable predictions for the neutron. The results obtained are α_n = 13.4±1.0 , β_n = 1.8±1.0 (10^-4fm^3), and γ⁽ⁿ⁾ _π = 57.6±1.8 (10^-4fm^4). New empirical information on the flavor wave functions of the f ₀(980) - and the a ₀(980) -meson is obtained.     

Geometric entanglement in valance-bond-solid state

Multipartite entanglement, measured by the geometric entanglement (GE), is discussed for integer spin Valance-Bond-Solid (VBS) state respectively with periodic boundary condition (PBC) and open boundary condition (OBC) in this paper. The optimization in the definition of geometric entanglement can be reduced greatly by exploring the symmetry of VBS state, and then the fully separable state can be determined explicitly. Numerical evaluation for GE by the random simulation is also implemented in order to demonstrate the validity of the reductions. Our calculations show that GE is saturated by a finite value with the increment of particle number, that means that the total entanglement for VBS state would be divergent under the thermodynamic limit. Moreover it is found that the scaling behavior of GE with spin number s is fitted as α log(s + β/s + γ)+δ, in which the values of the parameters α, β, γ, σ are only dependent on the parity of spin s. A comparison with entanglement entropy of VBS state is also made, in order to demonstrate the essential differences between multipartite and bipartite entanglement in this model.     

Analysis and correction of the measurement of the neutron lifetime

Corrections have been introduced into the result τ_β = 885.4 ± 0.9_stat ± 0.4_syst s of our measurements of the neutron lifetime. The corrected value is τ_β = 881.6 ± 0.8_stat ± 1.9_syst s.     

Similarity Transformations of Hermitian Hamiltonians and Pseudo-Hermitian Coupling Between Two Electromagnetic Modes

Pseudo-Hermitian Hamiltonians and pseudo-Hermitian coupling between two electromagnetic modes are analyzed by using similarity transformations of Hermitian Hamiltonians or of Hermitian operators, including a special metric and biorthogonal relations replacing the usual orthogonal relations used in quantum mechanics. The coupling between two electromagnetic (em) modes including certain decay and amplification processes is related to a coupling matrix G which has parity-time (PT) symmetry and which obeys the pseudo-Hermiticity condition ηGη⁻¹ = G ^† where η is a metric. The linear equations representing the pseudo-Hermitian coupling between the two em modes are diagonalized, in the interaction picture, by introducing ‘dressed’ αˉ and β~ operators which have real or pure imaginary eigenfrequencies. The commutation-relations (CR) for the α~ and β~ operators and for the two-mode operators ā and b~, in the interaction picture and under the condition of real eigenfrequencies are obtained by the use of the pseudo-Hermiticity property of the G matrix. These CR for real eigenfrequencies, are preserved in time without any Langevin noise terms.     

Quantum monte carlo studies of electron-electron interaction effects in conducting polymers

We discuss recent studies, using the quantum ensemble projector Monte Carlo (EPMC) method, of theoretical models of conducting polymers. Our focus is on the consequences of incorporating direct electron-electron interactions into the “standard” electron-phonon interaction models. Among the observables we examine one energetics of purely dimerized ground states, single solitons, soliton pairs, averaged spin and charge distributions, and local correlation functions.     

Theory of muon spin depolarization in condensed phases of hydrogen isotopes

A theory of muon spin depolarization in the molecular ion ( H₂μ)⁺(( D_2μ)) formed in a crystalline phase of hydrogen isotopes is presented. It is shown that the molecular ion ( H_2μ)⁺ has no time to thermalize during the muon lifetime, but after \tau\ll \tau_μ has time to transit to the lowest energy levels of the vibration‐rotation spectrum. The depolarization of the muon spin is determined by the interaction of the ion’s electric dipole moment with the lattice and by spin‐rotation interactions V_LS in the ion. This mechanism is analogous to that of “muonium”, replacing the hyperfine interaction by V_LS. The results can explain the experimental data and in particular the absence of a strong isotopic effect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Contribution to the theory of spin relaxation at finite temperatures in the odd-filling quantum Hall effect regime

Spin relaxation in a two-dimensional electron gas (2D EG) is treated as the establishment of equilibrium in a gas of spin excitons as a result of processes that change the number of spin excitons. Coalescence is the dominant channel above a temperature of the order of 1 K. The coalescence of excitons can occurr as a result of spin-orbit and Coulomb interactions in the 2D EG. The rate of coalescence falls exponentially at low temperatures. The relaxation time is calculated, and the critical temperature below which the main annihilation process becomes that due to the exciton-phonon interaction is determined. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 531–536 (25 October 1999)     

Isomeric state of 80Y and its role in the astrophysical rp-process

A careful investigation of the isomeric transition of the long-lived state at 228.5 keV excitation energy in ⁸⁰Y has been done. The HIGISOL facility at the Jyv?skyl? isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the electron spectra in clean background conditions. The measured internal conversion coefficient α_K = 0.50±0.07 allows unambiguous 1^- identification for the 228.5 keV first excited isomeric state in ⁸⁰Y. With a “bare" half-life of 6.8±0.5 s found in this work, this state is strongly populated in the rp-process during X-ray bursts and has therefore to be taken into account in X-ray burst model calculations. However, because of the similarity of the β-decay half-lives of isomeric and ground states, we find a maximum reduction in the effective β-decay lifetime of ⁸⁰Y of only 17±2%. Our results pave the way for a future investigation of the impact of the isomeric state on the “effective" ⁸⁰Y proton capture rate. Received: 14 March 2001 / Accepted: 10 July 2001     

On bound state computations in three- and four-electron atomic systems

A variational approach is developed for bound state calculations in three- and four-electron atomic systems. This approach can be applied to determine, in principle, an arbitrary bound state in three- and four-electron ions and atoms. Our variational wave functions are constructed from four- and five-body Gaussoids that respectively depend on six (r ₁₂, r ₁₃, r ₁₄, r ₂₃, r ₂₄, r ₃₄) and ten (r ₁₂, r ₁₃, r ₁₄, r ₁₅, r ₂₃, r ₂₄, r ₂₅, r ₃₄, r ₃₅ and r ₄₅) relative coordinates. The approach allows operating with the more than one electron spin functions. In particular, the trial wave functions for the ¹ S states in four-electron atomic systems include the two independent spin functions χ₁ = αβαβ + βαβα − βααβ − αββα and χ₂ = 2ααββ + 2ββαα − βααβ − αββα − βαβα − αβαβ. We also discuss the construction of variational wave functions for the excited 2³ S states in four- electron atomic systems.     

Beneficial effects of an ultra-fine α-SiC incorporation on the sinterability and mechanical properties of ZrB2

A fully dense ZrB₂ ceramic containing 10 vol. % ultra-fine α-SiC particulate was successfully hot pressed at 1900 °C for 20 min and 40–50 MPa of applied pressure. Faceted ZrB₂ grains (average size ≈3 μm) and SiC particles dispersed regularly characterized the base material. No extra secondary phases were found. The introduction of the ultra-fine α-SiC particulate was recognized as the key factor that enabled both the control of the diboride grain growth and the achievement of full density. The mechanical properties offered an interesting combination of data: 4.8±0.2 MPafracture toughness, 507±4 GPa Young’s modulus, 0.12 Poisson’sratio, and 835±35 MPa flexural strength at room temperature. The flexural strength measured at 1500 °C (in air) provided values of 300±35 MPa. The incorporated ultra-fine α-SiC particulate was fundamental, sinterability apart, to enhancing the strength and oxidation resistance of ZrB₂. The latter property was tested at 1450 °C for 20 h in flowing dry air. In such oxidizing conditions, the formation of a thin external borosilicate glassy coating supplied partial protection for the faces of the material exposed to the hot environment. The oxidation attack penetrated into the material’s bulk and created a 200-μm-thick zirconia scale. The SiC particulate included in the oxide scale, lost by active oxidation, left carbon-based inclusions in the formerly occupied sites. PACS 81.05.Je; 81.20.Ev; 81.70.Bt