We investigate the temperature dependence of the shear viscosity and spin diffusion in a two-dimensional Fermi gas with contact interactions, as realized in ultra-cold atomic gases. We describe the transport coefficients in terms of a Boltzmann equation and present a full numerical solution for the degenerate gas. In contrast to previous works we take the medium effects due to finite density fully into account. This effect reduces the viscosity to entropy ratio, $\eta/s$, by a factor of three, and similarly for spin diffusion. The trap averaged viscosity agrees well with recent measurements by Vogt et al. [Phys. Rev. Lett. 108, 070404 (2012)].Comment: 8 pages, 4 figures; published versio

Noninteracting insulating electronic states of matter can be classified according to their symmetries in terms of topological invariants which can be related to effective surface theories. These effective surface theories are in turn topologically protected against the effects of disorder. Topological crystalline insulators are, on the other hand, trivial in the sense of the above classification but still possess surface modes. In this work we consider an extension of the Bernevig-Hughes-Zhang model that describes a point group insulator. We explicitly show that the surface properties of this state can be as robust as in topologically nontrivial insulators, but only if the Sz-component of the spin is conserved. However, in the presence of Rashba spin-orbit coupling this protection vanishes and the surface states localize, even if the crystalline symmetries are intact on average.

Octupole vibrational states were studied in the nucleus 150 Nd via inelastic proton scattering with 10.9-MeV protons, which are an excellent probe to excite natural parity states. For the first time in 150 Nd, both the scattered protons and the γ rays were detected in coincidence, giving the possibility to measure branching ratios in detail. Using the coincidence technique, the B(E1) ratios of the decaying transitions for 10 octupole vibrational states and other negative-parity states to the yrast band were determined and compared to the Alaga rule. The positive and negative-parity states revealed by this experiment are compared with interacting boson approximation calculations performed in the spdf boson space. The calculations are found to be in good agreement with the experimental data, for both positive and negative-parity states.

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