Critical current of 3He-A in narrow channels

The critical current Jc of superfluid 3He-A in 0.8-μm-diam channels has been measured by the observation of the pressure difference along the channels versus the mass current. During warming Jc was found to decrease by about 30% at TBA(cyl) and by another 30% at TBA; TBA(cyl) is the reduced B→A transition temperature in the narrow flow channels, with TBA(cyl)TBA=0.92 at 27.4 bars. Above TBA a second dissipative mechanism was observed at lower currents. These features are believed to be associated with the ends of the channels.Peer reviewe

Critical temperature of superconductor/ferromagnet bilayers

Superconductor/ferromagnet bilayers are known to exhibit nontrivial dependence of the critical temperature T_c on the thickness d_f of the ferromagnetic layer. We develop a general method for investigation of T_c as a function of the bilayer's parameters. It is shown that interference of quasiparticles makes T_c(d_f) a nonmonotonic function. The results are in good agreement with experiment. Our method also applies to multilayered structures.Comment: 4 pages, 2 EPS figures; the style file jetpl.cls is included. Version 2: typos correcte

Unfinished History and Paradoxes of Quantum Potential. II. Relativistic Point of View

This is the second of the two related papers analysing origins and possible explanations of a paradoxical phenomenon of the quantum potential (QP). It arises in quantum mechanics'(QM) of a particle in the Riemannian $n$-dimensional configurational space obtained by various procedures of quantization of the non-relativistic natural Hamilton systems. Now, the two questions are investigated: 1)Does QP appear in the non-relativistic QM generated by the quantum theory of scalar field (QFT) non-minimally coupled to the space-time metric? 2)To which extent is it in accord with quantization of the natural systems? To this end, the asymptotic non-relativistic equation for the particle-interpretable wave functions and operators of canonical observables are obtained from the primary QFT objects. It is shown that, in the globally-static space-time, the Hamilton operators coincide at the origin of the quasi-Euclidean space coordinates in the both altenative approaches for any constant of non-minimality $\tilde\xi$, but a certain requirement of the Principle of Equivalence to the quantum field propagator distinguishes the unique value $\tilde\xi = 1/6$. Just the same value had the constant $\xi$ in the quantum Hamiltonians arising from the traditional quantizations of the natural systems: the DeWitt canonical, Pauli-DeWitt quasiclassical, geometrical and Feynman ones, as well as in the revised Schr\"{o}dinger variational quantization. Thus, QP generated by mechanics is tightly related to non-minimality of the quantum scalar field. Meanwhile, an essential discrepancy exists between the non-relativistic QMs derived from the two altenative approaches: QFT generate a scalar QP, whereas various quantizations of natural mechanics, lead to PQs depending on choice of space coordinates as physical observables and non-vanishing even in the flat space if the coordinates are curvilinear.Comment: 15 pages, based on the plenary talk at the A. Z. Petrov Centenary Memorial International Symposium, 1-7.11.2010, Kazan, Russia. Few errors are corrected and minor improving changes are introduced into Chapters 4 -

On the scalar sector of the covariant graviton two-point function in de Sitter spacetime

We examine the scalar sector of the covariant graviton two-point function in de Sitter spacetime. This sector consists of the pure-trace part and another part described by a scalar field. We show that it does not contribute to two-point functions of gauge-invariant quantities. We also demonstrate that the long-distance growth present in some gauges is absent in this sector for a wide range of gauge parameters.Comment: 15 pages, no figures, LaTeX, considerably shortene

Search for the ac Josephson effect in superfluid 3He

Experiments testing for the existence of the ac Josephson effect in superfluid 3He, analogous to phenomena observed in superconducting microbridges, have been performed. Small holes were employed as the weak link between two reservoirs filled with 3He; several different orifice geometries were tried. Simple model calculations suggest that steps in the flow characteristics should be observable with our resolution when an ac pressure modulation is applied across the weak link. We found that such effects do not exist for the parameter values used in our experiments.Peer reviewe