1,560 research outputs found
Topological invariants for spin-orbit coupled superconductor nanowires
We show that a spin-orbit coupled semiconductor nanowire with Zeeman
splitting and s-wave superconductivity is in symmetry class BDI (not D as is
commonly thought) of the topological classification of band Hamiltonians. The
class BDI allows for an integer Z topological invariant equal to the number of
Majorana fermion (MF) modes at each end of the quantum wire protected by the
chirality symmetry (reality of the Hamiltonian). Thus it is possible for this
system (and all other d=1 models related to it by symmetry) to have an
arbitrary integer number, not just 0 or 1 as is commonly assumed, of MFs
localized at each end of the wire. The integer counting the number of MFs at
each end reduces to 0 or 1, and the class BDI reduces to D, in the presence of
terms in the Hamiltonian that break the chirality symmetry.Comment: 4+ pages, no figure
Diamagnetic susceptibility obtained from the six-vertex model and its implications for the high-temperature diamagnetic state of cuprate superconductors
We study the diamagnetism of the 6-vertex model with the arrows as directed
bond currents. To our knowledge, this is the first study of the diamagnetism of
this model. A special version of this model, called F model, describes the
thermal disordering transition of an orbital antiferromagnet, known as
d-density wave (DDW), a proposed state for the pseudogap phase of the high-Tc
cuprates. We find that the F model is strongly diamagnetic and the
susceptibility may diverge in the high temperature critical phase with power
law arrow correlations. These results may explain the surprising recent
observation of a diverging low-field diamagnetic susceptibility seen in some
optimally doped cuprates within the DDW model of the pseudogap phase.Comment: 4.5 pages, 2 figures, revised version accepted in Phys. Rev. Let
Proposal to stabilize and detect half-quantum vortices in strontium ruthenate thin films: Non-Abelian braiding statistics of vortex matter in a superconductor
We propose a simple way to stabilize half-quantum vortices in superconducting
strontium ruthenate, assuming the order parameter is of chiral
symmetry, as is suggested by recent experiments. The method, first given by
Salomaa and Volovik in the context of Helium-3, is very naturally suited for
strontium ruthenate, which has a layered, quasi-two-dimensional, perovskite
crystal structure. We propose possible experiments to detect their non
abelian-braiding statistics. These experiments are of potential importance for
topological quantum computation
Topological superfluids on a lattice with non-Abelian gauge fields
Two-component fermionic superfluids on a lattice with an external non-Abelian
gauge field give access to a variety of topological phases in presence of a
sufficiently large spin imbalance. We address here the important issue of
superfluidity breakdown induced by spin imbalance by a self-consistent
calculation of the pairing gap, showing which of the predicted phases will be
experimentally accessible. We present the full topological phase diagram, and
we analyze the connection between Chern numbers and the existence of
topologically protected and non-protected edge modes. The Chern numbers are
calculated via a very efficient and simple method.Comment: 6 pages, 5 figures to be published in Europhysics Letter
Shock formation and the ideal shape of ramp compression waves
We derive expressions for shock formation based on the local curvature of the
flow characteristics during dynamic compression. Given a specific ramp adiabat,
calculated for instance from the equation of state for a substance, the ideal
nonlinear shape for an applied ramp loading history can be determined. We
discuss the region affected by lateral release, which can be presented in
compact form for the ideal loading history. Example calculations are given for
representative metals and plastic ablators. Continuum dynamics (hydrocode)
simulations were in good agreement with the algebraic forms. Example
applications are presented for several classes of laser-loading experiment,
identifying conditions where shocks are desired but not formed, and where long
duration ramps are desired
Effect of Water Vapor on the Oxidation Behavior of the Eutectic High‐Temperature Alloy Mo‐20Si‐52.8Ti
Herein, the effect of water vapor on the oxidation resistance of the alloy Mo-20Si-52.8Ti (at%) is investigated. The alloy is oxidized in dry, wet, as well as in in situ changing atmospheres at 1100 C. The oxidation kinetics changes from nearly parabolic to linear if water vapor is present in oxidizing atmosphere. Under all conditions, the oxide scales consist of an outer TiO and a TiO─SiO duplex layer underneath. In wet atmosphere, the thicknesses of the two regions substantially increase indicating a severe ingress of water vapor. The inferior oxidation resistance in wet environment is primarily rationalized by the fast diffusion of HO through SiO
Topologically non-trivial superconductivity in spin-orbit coupled systems: Bulk phases and quantum phase transitions
Topologically non-trivial superconductivity has been predicted to occur in
superconductors with a sizable spin-orbit coupling in the presence of an
external Zeeman splitting. Two such systems have been proposed: (a) s-wave
superconductor pair potential is proximity induced on a semiconductor, and (b)
pair potential naturally arises from an intrinsic s-wave pairing interaction.
As is now well known, such systems in the form of a 2D film or 1D nano-wires in
a wire-network can be used for topological quantum computation. When the
external Zeeman splitting crosses a critical value , the
system passes from a regular superconducting phase to a non-Abelian topological
superconducting phase. In both cases (a) and (b) we consider in this paper the
pair potential is strictly s-wave in both the ordinary and the
topological superconducting phases, which are separated by a topological
quantum critical point at , where is the chemical potential. On the other hand, since , the Zeeman splitting required for the topological phase () far exceeds the value () above which an s-wave
pair potential is expected to vanish (and the system to become
non-superconducting) in the absence of spin-orbit coupling. We are thus led to
a situation that the topological superconducting phase appears to set in a
parameter regime at which the system actually is non-superconducting in the
absence of spin-orbit coupling. In this paper we address the question of how a
pure s-wave pair potential can survive a strong Zeeman field to give rise to a
topological superconducting phase. We show that the spin-orbit coupling is the
crucial parameter for the quantum transition into and the robustness of the
topologically non-trivial superconducting phase realized for .Comment: as published in the focus issue on Topological Quantum Computation,
New J. Phys. 13 (2011
Force distributions near the jamming and glass transitions
We calculate the distribution of interparticle normal forces near the
glass and jamming transitions in model supercooled liquids and foams,
respectively. develops a peak that appears near the glass or jamming
transitions, whose height increases with decreasing temperature, decreasing
shear stress and increasing packing density. A similar shape of was
observed in experiments on static granular packings. We propose that the
appearance of this peak signals the development of a yield stress. The
sensitivity of the peak to temperature, shear stress and density lends credence
to the recently proposed generalized jamming phase diagram.Comment: 4 pages, 3 postscript figures;Version 3 replaces figure 1 and removes
figure 2 from version 1. Significant rewording of version 1 to emphasize the
formation of peak in P(F) when these systems jam along five different routes
of the recently proposed jamming phase diagram. Version 2 displayed the
incorrect abstrac
Nonlinear Stress Fluctuation Dynamics of Sheared Disordered Wet Foam
Sheared wet foam, which stores elastic energy in bubble deformations, relaxes
stress through bubble rearrangements. The intermittency of bubble
rearrangements in foam leads to effectively stochastic drops in stress that are
followed by periods of elastic increase. We investigate global characteristics
of highly disordered foams over three decades of strain rate and almost two
decades of system size. We characterize the behavior using a range of measures:
average stress, distribution of stress drops, rate of stress drops, and a
normalized fluctuation intensity. There is essentially no dependence on system
size. As a function of strain rate, there is a change in behavior around shear
rates of .Comment: accepted to Physical Review
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