The effect of pressure on the resistivity of a gold-chromium Kondo alloy and on the low temperature phonon resistivity of pure gold

The electrical resistivity of the Kondo alloy Au (20ppm Cr) and of pure gold has been determined in the temperature range 1.3 – 20 K at pressures up to 80 kbar. For pure gold the pressure dependence of the temperature dependent part of the lattice resistivity can be explained fairly well by the Bloch-Grüneisen theory. Expressions for the volume dependence of the ideal lattice resistivity and of the Debye-temperature for gold are derived. — The Kondo temperatureT _K of Au(Cr) is found to increase with pressure to more than twice the value atp=0 kbar.Therefrom the volume dependence of the effective exchange constantJ is calculated. The results are similar as in other Kondo alloys described previously.     

Some analytic results concerning the mass spectrum of Yang-Mills gauge theories on a torus

When non-abelian gauge fields are enclosed in a box with periodic boundary conditions, the spectrum of the hamiltonian becomes discrete and the energy values can be expanded in a power series of $\text{ifλ = g}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(g:}\text{renormalized coupling constant)}$. A method to obtain these expansions is explained and worked out to one-loop order. No numbers for the low-lying levels are given here, but some interesting properties of the mass spectrum already become visible.     

Computation of the action for on-shell improved lattice gauge theories at weak coupling

The coefficient in Symanzik's improved lattice action for (pure) SU(2) and SU(3) gauge theories are determined to one-loop order by requiring the absence of leading scaling violations in a set of on-shell quantities, which arise in a world where two dimensions are compactified in a twisted manner.     

SubthresholdK + production in proton-nucleus collisions

We analyzed theK ⁺ production at projectile energies below the free nucleon-nucleon threshold in proton-nucleus collisions and studied the contribution from different reaction channels to this process. It was shown that the secondary pion-nucleon (+N+K ⁺) channel significantly prevails over the direct (p+N+N+K ⁺) one. The momentum and angularK ⁺ spectra were calculated in the framework of different production channels in order to propose experimental measurements which allow to distinguish the mechanisms discussed. We also studiedK ⁺ d correlations and considered the deuteron reabsorption in the nuclear medium as well as the fast deuteron background. The features ofK ⁺ p correlations related to the different production channels were analyzed as well.     

Die Hysterese der Adsorptions- und Desorptionsisothermen an porösen Silicagelen und Aluminiumoxiden

In selected groups of amorphous silica gels and finely crystalline aluminium oxides, hysteresis loops between the adsorption- and desorption isotherms of water were determined. The total volumes of the pore systems were analysed with the aid of the differential quotients of the hysteresis loops. In the group of silica gels relationships will be demonstrated between the precipitation of polysilicid acids and the distribution of the pore volume in the xerogels. In the group of aluminium oxides the influence of sintering at high temperatures on the distribution of the pore volume will be described. The hysteresis loops and especially the differential quotients distinctly differentiate specific properties of the used materials with their variables pore systems. An apparatus was used which recorded weights of water (= volumes and volume differences) with high sensitivity over the entire range p/po = 0 to 0,95. The appearance of hysteresis according to the fundamental theory was a sign that in this range adsorption and desorption of the liquid phase water took place in mesopores.     

Crystal-quasicrystal interfaces on Al-Pd-Mn

Two decades after their discovery, quasicrystals continue to fascinate our imagination. Even though there remain many outstanding questions about the basic structure, our focus has lately been shifting beyond the basic structural aspects, towards the search for interesting physical properties and technological applications. In this regard, undoubtedly, thin film growth on quasicrystal surfaces promises to be a very fertile ground. Despite their true long-range orientational order, quasicrystals possess forbidden fivefold or tenfold point-group symmetries and lack translational periodic order. Therefore, the interface between a quasicrystal and a crystal is of immense scientific interest, because it can metastabilize previously unknown structures with unique properties and potentially disclose structural mysteries of quasicrystalline surfaces. In our studies, we used various electron probes and observed that binary Al alloys exist as commensurate single crystals on the fivefold- and threefold-symmetry surfaces of the Al-Pd-Mn alloy. Thus, epitaxial growth conditions, like lattice and chemical matching observed in crystals are apparently satisfied on a local scale. We have also grown Al films at different temperatures on quasicrystal surfaces, and found that above RT Al readily diffuses into the bulk quasicrystal leading to a huge increase of its Debye temperature, implying that the quasicrystalline structure contains vacancies, which are filled with the additional Al. For thin films grown at RT, epitaxy locks the Al atoms to a strained quasicrystalline lattice, whereas for thicker films, excess strain energy cannot be supported and the structure relaxes to the bulk stable face-centered cubic phase by breaking into multi-twinned domains. The crystal-quasicrystal transformations also present an opportunity to investigate the electronic structure in a comparative way. We highlight a relevant result on the filling of the Mn 3d band in Al-Pd-Mn upon quasicrystal formation that gives rise to the pseudo gap.     

Topology of lattice gauge fields

Non-Abelian gauge fields on a four-dimensional hypercubic lattice with small action density [Tr{U( )} for SU(2) gauge fields] are shown to carry an integer topological chargeQ, which is invariant under continuous deformations of the field. A concrete expression forQ is given and it is verified thatQ reduces to the familiar Chern number in the classical continuum limit.Work supported in part by Schweizerischer Nationalfonds     

Pressure dependence of the electrical resistivity of Ag(Mn), both in the dilute limit and in the spin glass regime

The electrical resistivity of the dilute spin glass alloys Ag(1,540 ppm Mn) and Ag(1,015 ppm Mn) has been measured from 1.3–30 K at pressures up to 70 kbars. The temperature of the resistance maximum,T _m , is found to shift to higher temperatures, this shift being stronger for the more concentrated alloys.Additionally an Ag(20 ppm Mn) Kondo-alloy has been investigated. Application of pressure causes an increase of the Kondo temperatureT _K from which the volume dependence of the effective exchange constantJ is derived.With this information theT _m -shift in the spin glass alloys can be understood in a qualitative and quantitative manner within Larsen's model.     

Precise determination of the unperturbed 8B neutrino spectrum

A measurement of the final state distribution of the (8)B β decay, obtained by implanting a (8)B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyv?skyl? [O. S. Kirsebom et al., Phys. Rev. C 83, 065802 (2011)]. It shows discrepancies with previously measured spectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, the neutrino spectrum is for the first time directly extracted from the measured final state distribution, thus avoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data, this leads to an improvement of the overall errors and the extension of the neutrino spectrum at high energy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of the solar neutrino flux as a function of energy.