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[en] Our recent experiments on YbRhSi showed - aside from the well known antiferromagnetic transition at 70 mK - two new phases below 10 mK and 2 mK respectively1. The latter is practically coinciding with superconductivity. Evidence for these findings came from magnetic susceptibility measurements, dc as well as ac, performed at the Walther-Meissner Institut in Garching. The 2 mK A-phase transition is a hybrid electronic-nuclear spin transition and it extends to fields of 23 mT where it is suppressed to below our detection limit of 800 K. In addition, specific heat data show, that at this transition a large entropy is involved coming from the nuclear spins of the Yb isotopes. Here we present additional, unpublished results around and below this temperature up to the Quantum Critical Point at 60 mT. Also, we re-analyzed previous data on the magnetic susceptibility of CeCu taken in Garching and Cornell in 1994 2. The results are very similar to those of YbRhSi and it is very likely that the same mechanism holds in both systems.
[en] The deformation properties of two isotopic chains Yb and Hf from neutron deficient up to neutron drip lines using an axially deformed relativistic mean field (RMF) formalism were studied. A change in sign of ground state hexadecapole moments from positive to negative value at A=180 and again from negative to positive at A=198 for Hf isotopes with TM1 parameter set is found at A=178 and A=196 from positive to negative and negative to positive values respectively
[en] In Hartree-Fock calcualtions using nonrelativistic and relativistic models we see a change in sign from positive to negative of the hexadecapole moment with mass number around A=170. Analysis of Hartree-Fock orbitals shows that a group of neutron orbits with large negative hexadecapole moments occur together at the Fermi surface near N=100 and are responsible for the shape change
[en] The orientation of the angular momentum in triaxial nuclei has been investigated in a three-dimensional cranked-HFB formalism. Some quasiparticle excitations are found to favour cranking about a non-principal axis for particular combinations of shell filling and triaxial shape. This effect also exists when the energy of the rotating core is added, at least for low spins, which is shown in a complete cranking calculation for 84Y. (orig.)
[en] To verify the apparent large enhancement of the radiative strength function in light and medium nuclei, the 56Fe(n,2gamma)57Fe reaction was measured. The two-step cascade intensities with soft primary intensities confirm the enhancement. The combined results have been published in Physical Review Letters and featured in the Physics News Update. Data for the Yb isotopes have been combined to examine the systematics of level densities and strength function in three Yb isotopes. A paper on these results have been accepted for publication in Physical Review C. Analysis of the gamma rays from neutron induced reactions on 48Ti have been measured and analyzed for neutron energies from 1 to 250 MeV
[en] The investigation of the heavy fermion compound YbRhSi allows new insights concerning the interplay of quantum phase transitions and superconductivity. The compound shows at 70 mK antiferromagnetic order which can be further suppressed to a quantum critical point. Recently, at 2 mK a superconducting state was discovered. Due to the ordering of the nuclear spin of Yb and Yb before the superconducting state emerges it is a matter of particular interest to investigate the evolution of the superconductivity in single crystals with pure zero and non-zero nuclear spins of the Yb-isotopes. To this end, we first need to optimize the metallothermic reduction of the rare earth element as the isotopes are only available as oxides. Furthermore, we present the optimization of down-scaling in mass the single crystal growth and we report two ways to regaining ytterbium from foreign phase YbRhIn.
[en] Estimate of ionization yield and selectivity in multi-step photoionization is of interest in studies related to trace analysis and laser isotope separation. Analytical expressions of ionization yield for the desired and interfering isotopes have been derived by solving rate equations for three-step photoionization. The partial overlap of absorption lines of the isotopes and the charge exchange of the ions of the desired isotope with the atoms of the interfering isotope have been considered. The ionization yield and the isotopic selectivity of the photoionization process are calculated for ytterbium isotopes, considering various atomic and laser parameters. Numerical results have been discussed, showing the effect of both factors on the ionization yield and the isotopic selectivity of the process. (author)