Quantum critical behaviour in Ce3Pd20Si6?

The cage compound Ce₃Pd₂₀Si₆ has recently been shown to undergo two successive low-temperature phase transitions which are strongly affected by an applied magnetic field. Here we show that, as the lower, probably antiferromagnetic transition is suppressed to zero in a field slightly above 1 T, the electrical resistivity shows a non-Fermi-liquid-like linear-in-T   temperature dependence while it follows the usual Fermi liquid T²$T^2$ temperature dependence both at smaller and larger fields. This suggests that a field-induced quantum critical point exists in Ce₃Pd₂₀Si₆.     

Mechanism of pion production in αp scattering at 1 GeV/nucleon

An analysis of the experimental data on one-pion and two-pion production in the p(??, ????)X reaction studied in a semi-exclusive experiment at an energy of E _?? = 4.2 GeV has been performed. The obtained results demonstrate that the inelastic ??-particle scattering on the proton at the energy of the experiment proceeds either through excitation and decay of the ?? resonance in the projectile ?? particle, or through excitation in the target proton of the Roper resonance, which decays into a nucleon and a pion, or a nucleon and a ?? meson??a system of two pions in the isospin I = 0, S-wave state.     

Direct bandgap optical transitions in Si nanocrystals

JETP Letters - The effect of quantum confinement on the direct bandgap of spherical Si nanocrystals has been modelled theoretically. We conclude that the energy of the direct bandgap at the...     

Resonant acceptor states in uniaxially strained semiconductors

A new approach to calculating the parameters of resonant states is proposed, which also makes it possible to determine the probabilities of the resonant scattering and capture probabilities at the resonant state. This approach is based on the application of the method of configuration interaction, which was proposed for the first time by Fano for an analysis of field ionization of the helium atom. Following Fano, use is made of two different Hamiltonians of the initial approximation for the states of continuum and the initial local state. Following Dirac, the wave functions are constructed in the same way as in the general theory of scattering. A detailed analysis and specific calculations are made for resonant acceptor states in uniaxially strained germanium under a pressure directed along the [001] and [111] axes.     

Theoretical modeling of excitation and de-excitation processes of Er in SiO2 with Si nanocrystals

We construct the theory of carriers confined in Si quantum dots with finite energy barriers for electrons and holes in the framework of the multiband effective mass theory. We apply this theory for theoretical modeling of the excitation of erbium inside and outside of Si nanocrystals in SiO₂ matrix due to the Auger process induced by the recombination of a confined electron-hole pair as well as the intraband transitions of “hot” confined carriers. Auger de-excitation processes of the Er³⁺ ion leading to the quenching of erbium luminescence are discussed as well.     

Magnetic properties of the low dimensional spin system (VO)PO:ESR and susceptibility

Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)₂P₂O₇. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine J =51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K. Received: 22 December 1997 / Accepted: 17 March 1998     

Two-pion decay of the P 11(1440) resonance excited in αp Scattering at 1 GeV/nucleon

Semiexclusive measurements of the two-pion production reaction p(α, α′)pππ have been carried out at an energy of E _α = 4.2 GeV at the Saturne-II (Saclay) accelerator with the SPES4-π installation. The two-pion production reaction was investigated by simultaneous registration of the scattered α particle and the secondary proton. The obtained results show that the two-pion decay of the P ₁₁(1440) resonance excited in the target proton in this reaction proceeds predominantly with emission of two pions in the isospin I = 0, S-wave state. The text was submitted by the authors in English. the SPES4-π Collaboration     

Observation of the magnetic domain structure in Cu<Subscript>0.47</Subscript>Ni<Subscript>0.53</Subscript> thin films at low temperatures

We report on the first experimental visualization of domain structure in films of weakly ferromagnetic Cu_0.47Ni_0.53 alloy with different thickness at liquid helium temperatures. Improved high-resolution Bitter decoration technique was used to map the magnetic contrast on the surface of the films well below the Curie temperature T_Curie (∼60 K). In contrast to magnetic force microscopy, this technique allowed visualization of the domain structure without its disturbance while the larger areas of the sample were probed. Maze-like domain patterns, typical for perpendicular magnetic anisotropy, were observed. The average domain width was found to be about 100 nm. The article is published in the original.     

Amorphization of bulk TiNi-based alloys by severe plastic deformation under high pressure torsion

The structure of bulk samples of Ti_49.4Ni_50.6 alloy after severe plastic deformation by torsion (SPDT) under high pressure have been studied by transmission and scanning electron microscopies. It is found that SPDT by five to seven turns led to almost complete alloy amorphization.     

Melt‐spun Eu8Ga16–xGe30+x Clathrates

Intermetallic clathrates are promising materials for thermoelectric applications. This is not only due to their low thermal and high electrical conductivities (“phonon glass – electron crystal”) but also due to the expectation that they are semiconductors and thus have large thermopower values. Band structure calculations of the stoichiometric compound Eu₈Ga₁₆Ge₃₀ indeed yield a semiconducting ground state. However, with conventional synthesis methods the exact 8:16:30 stoichiometry could not be reached. Herein we use the melt‐spinning technique to obtain Eu₈Ga_16–xGe_30+x samples with smaller x than previously realized. The quenching procedure and the results of the characterization of the quenched phases by X‐ray powder diffraction and electron microscopy are presented. The electrical resistivity shows that, in contrast to conventional synthesis procedures, semiconducting compounds can be produced.