Quantum fluids in nanopores

We describe calculations of the properties of quantum fluids inside nanotubes of various sizes. Very small radius ($R$) pores confine the gases to a line, so that a one-dimensional (1D) approximation is applicable; the low temperature behavior of 1D $^4$He is discussed. Somewhat larger pores permit the particles to move off axis, resulting eventually in a transition to a cylindrical shell phase--a thin film near the tube wall; we explored this behavior for H$_2$. At even larger $R\sim 1$ nm, both the shell phase and an axial phase are present. Results showing strong binding of cylindrical liquids $^4$He and $^3$He are discussed.Comment: 8 pages, 4 figures, uses ws-ijmpb, graphicx, xspace; minor revisions from version published in Proc. 13th Intl. Conference on Recent Progress in Many-Body Theories (QMBT13), Buenos Aires, 200

Averaged null energy condition violation in a conformally flat spacetime

We show that the averaged null energy condition can be violated by a conformally coupled scalar field in a conformally flat spacetime in 3+1 dimensions. The violation is dependent on the quantum state and can be made as large as desired. It does not arise from the presence of anomalies, although anomalous violations are also possible. Since all geodesics in conformally flat spacetimes are achronal, the achronal averaged null energy condition is likewise violated.Comment: 11 page

Numerical solution of the Boltzmann equation for the collective modes of trapped Fermi gases

We numerically solve the Boltzmann equation for trapped fermions in the normal phase using the test-particle method. After discussing a couple of tests in order to estimate the reliability of the method, we apply it to the description of collective modes in a spherical harmonic trap. The numerical results are compared with those obtained previously by taking moments of the Boltzmann equation. We find that the general shape of the response function is very similar in both methods, but the relaxation time obtained from the simulation is significantly longer than that predicted by the method of moments. It is shown that the result of the method of moments can be corrected by including fourth-order moments in addition to the usual second-order ones and that this method agrees very well with our numerical simulations.Comment: 13 pages, 8 figures, accepted for publication in Phys. Rev.

Theory of a Magnetically-Controlled Quantum-Dot Spin Transistor

We examine transport through a quantum dot coupled to three ferromagnetic leads in the regime of weak tunnel coupling. A finite source-drain voltage generates a nonequilibrium spin on the otherwise non-magnetic quantum dot. This spin accumulation leads to magnetoresistance. A ferromagnetic but current-free base electrode influences the quantum-dot spin via incoherent spin-flip processes and coherent spin precession. As the dot spin determines the conductance of the device, this allows for a purely magnetic transistor-like operation. We analyze the effect of both types of processes on the electric current in different geometries.Comment: 7 pages, 6 figure

The Refractive Index of Silicon at Gamma Ray Energies

The index of refraction n(E_{\gamma})=1+\delta(E_{\gamma})+i\beta(E_{\gamma}) is split into a real part \delta and an absorptive part \beta. The absorptive part has the three well-known contributions to the cross section \sigma_{abs}: the photo effect, the Compton effect and the pair creation, but there is also the inelastic Delbr\"uck scattering. Second-order elastic scattering cross sections \sigma_{sca} with Rayleigh scattering (virtual photo effect), virtual Compton effect and Delbr\"uck scattering (virtual pair creation) can be calculated by integrals of the Kramers-Kronig dispersion relations from the cross section \sigma_{abs}. The real elastic scattering amplitudes are proportional to the refractive indices \delta_{photo}, \delta_{Compton} and \delta_{pair}. While for X-rays the negative \delta_{photo} dominates, we show for the first time experimentally and theoretically that the positive \delta_{pair} dominates for \gamma rays, opening a new era of \gamma optics applications, i.e. of nuclear photonics.Comment: 4 pages, 3 figure

Barrier transmission of Dirac-like pseudospin-one particles

We address the problem of barrier tunneling in the two-dimensional T_3 lattice (dice lattice). In particular we focus on the low-energy, long-wavelength approximation for the Hamiltonian of the system, where the lattice can be described by a Dirac-like Hamiltonian associated with a pseudospin one. The enlarged pseudospin S = 1 (instead of S = 1/2 as for graphene) leads to an enhanced "super" Klein tunneling through rectangular electrostatic barriers. Our results are confirmed via numerical investigation of the tight-binding model of the lattice. For a uniform magnetic field, we discuss the Landau levels and we investigate the transparency of a rectangular magnetic barrier. We show that the latter can mainly be described by semiclassical orbits bending the particle trajectories, qualitatively similar as it is the case for graphene. This makes it possible to confine particles with magnetic barriers of sufficient width