80 research outputs found
Domain Walls in Superfluid 3He-B
We consider domain walls between regions of superfluid 3He-B in which one
component of the order parameter has the opposite sign in the two regions far
from one another. We report calculations of the order parameter profile and the
free energy for two types of domain wall, and discuss how these structures are
relevant to superfluid 3He confined between two surfaces.Comment: 6 pages with 3 figures. Conference proceedings of QSF 2004, Trento,
Ital
Theory of Nonequilibrium Spin Transport and Spin Transfer Torque in Superconducting-Ferromagnetic Nanostructures
Spin transport currents and the spin-transfer torques in voltage-biased
superconducting-ferromagnetic nanopillars (SFNFS point contacts) are computed.
We develop and implement an algorithm based on the Ricatti formulation of the
quasiclassical theory of superconductivity to solve the time-dependent boundary
conditions for the nonequilibrium Green's functions for spin transport through
the ferromagnetic interfaces. A signature of the nonequilibrium torque is a
component perpendicular to the plane spanned by the two ferromagnetic moments.
The perpendicular component is absent in normal-metal-ferromagnetic nanopillars
(NFNFN) contacts, but is shown to have the same order of magnitude as the
in-plane torque for non-equilibrium SFNFS contacts. The out-of-plane torque is
due to the rotation of quasiparticle spin by the exchange fields of the
ferromagnetic layers. In the ballistic limit the equilibrium torque is related
to the spectrum of spin-polarized Andreev bound states, while the {\sl ac}
component, for small bias voltages, is determined by the nearly adiabatic
dynamics of the Andreev bound states. The nonlinear voltage dependence of the
non-equilibrium torque, including the subharmonic gap structure and the
high-voltage asymptotics, is attributed to the interplay between multiple
Andreev reflections, spin filtering and spin mixing. These properties of spin
angular momentum transport may be exploited to control the state of
nanomagnets.Comment: 15 pages, 14 figure
``Cosmological'' scenario for A-B phase transition in superfluid 3He
At a very rapid superfluid transition in He, follows after a reaction
with single neutron, the creation of topological defects (vortices) has
recently been demonstrated in accordance with the Kibble-Zurek scenario for the
cosmological analogue. We discuss here the extension of the Kibble-Zurek
scenario to the case when alternative symmetries may be broken and different
states nucleated independently. We have calculated the nucleation probability
of the various states of superfluid He during a superfluid transition. Our
results can explain the transition from supercooled phase to the phase,
triggered by nuclear reaction. The new scenario is an alternative to the
well-known ``baked Alaska'' scenario.Comment: RevTex file, 4 pages, 3 figures, submitted to Phys. Rev. Let
Superfluid Phase Transitions in Dense Neutron Matter
The phase transitions in a realistic system with triplet pairing, dense
neutron matter, have been investigated. The spectrum of phases of the
model, which adequately describes pairing in this system, is
analytically constructed with the aid of a separation method for solving BCS
gap equation in states of arbitrary angular momentum. In addition to solutions
involving a single value of the magnetic quantum number (and its negative),
there exist ten real multicomponent solutions. Five of the corresponding
angle-dependent order parameters have nodes, and five do not. In contrast to
the case of superfluid He, transitions occur between phases with nodeless
order parameters. The temperature dependence of the competition between the
various phases is studied.Comment: 11 pages, 2 figure
Universalities of Triplet Pairing in Neutron Matter
The fundamental structure of the full set of solutions of the BCS
pairing problem in neutron matter is established. The relations between
different spin-angle components in these solutions are shown to be practically
independent of density, temperature, and the specific form of the pairing
interaction. The spectrum of pairing energies is found to be highly degenerate.Comment: 11 page
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The Evolution of Low-Level Radioactive Waste (LLW) Disposal Practices at the Savannah River Site Coupled with Vigorous Stakeholder Interaction
Low-level radioactive waste (LLW) disposal practices at SRS evolved from trench disposal with little long-term performance basis to disposal in robust concrete vaults, again without modeling long-term performance. Now, based on an assessment of long-term performance of various waste forms and methods of disposal, the LLW disposal program allows for a ''smorgasbord'' of various disposal techniques and waste forms, all modeled to ensure long-term performance is understood. New disposal techniques include components-in-grout, compaction/volume reduction prior to disposal, and trench disposal of extremely low activity waste. Additionally, factoring partition coefficient (Kd) measurements based on waste forms has been factored into performance models. This paper will trace the development of the different disposal methods, and the extensive public communications effort that resulted in endorsement of the changes by the SRS Citizens Advisory Board
Phase Diagram of the Two-Channel Kondo Lattice
The phase diagram of the two-channel Kondo lattice model is examined with a
Quantum Monte Carlo simulation in the limit of infinite dimensions.
Commensurate (and incommensurate) antiferromagnetic and superconducting states
are found. The antiferromagnetic transition is very weak and continuous;
whereas the superconducting transition is discontinuous to an odd-frequency
channel-singlet and spin-singlet pairing state.Comment: 5 pages, LaTeX and 4 PS figures (see also cond-mat/9609146 and
cond-mat/9605109
Staggered Pairing Phenomenology for UPd_2Al_3 and UNi_2Al_3
We apply the staggered-pairing Ginzburg-Landau phenomenology to describe
superconductivity in UPd_2Al_3 and UNi_2Al_3. The phenomenology was applied
successfully to UPt_3 so it explains why these materials have qualitatively
different superconducting phase diagrams although they have the same
point-group symmetry. UPd_2Al_3 and UNi_2Al_3 have a two-component
superconducting order parameter transforming as an H-point irreducible
representation of the space group. Staggered superconductivity can induce
charge-density waves characterized by new Bragg peaks suggesting experimental
tests of the phenomenology.Comment: 4 pages, REVTeX, 2 Postscript figure
Fluctuation Conductivity in Unconventional Superconductors near Critical Disorder
The fluctuation conductivity in bulk superconductors with
non s-wave pairing and with nonmagnetic disorder of strength is studied at
low and within the Gaussian approximation. It is shown by assuming a quasi
two-dimensional (2D) electronic state that, only if the gap function
d_\mu({\p}) is, as in a 2D p-wave pairing state, linear in the in-plane
(relative) momentum {\p}_\perp, the in-plane fluctuation conductivity on the
line is weakly divergent in low limit. The present result may be
useful in clarifying the true gap function of spin-triplet
through resistivity measurements.Comment: 8 pages, 1 figure, to be published in J. Phys. Soc. Jpn. 70, No.10
(2001
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