627 research outputs found
Rotating vortex dipoles in ferromagnets
Vortex-antivortex pairs are localized excitations and have been found to be
spontaneously created in magnetic elements. In the case that the vortex and the
antivortex have opposite polarities the pair has a nonzero topological charge,
and it behaves as a rotating vortex dipole. We find theoretically, and confirm
numerically, the form of the energy as a function of the angular momentum of
the system and the associated rotation frequencies. We discuss the process of
annihilation of the pair which changes the topological charge of the system by
unity while its energy is monotonically decreasing. Such a change in the
topological charge affects profoundly the dynamics in the magnetic system. We
finally discuss the connection of our results with Bloch Points (BP) and the
implications for BP dynamics.Comment: 6 pages, 2 figure
Quasiquarks in two stream system
We study the collective quark excitations in an extremely anisotropic system
of two interpenetrating streams of the quark-gluon plasma. In contrast to the
gluon modes, all quark ones appear to be stable in such a system. Even more,
the quark modes in the two-stream system are very similar to those in the
isotropic plasma.Comment: 4 pages, 2 figures, minor corrections, to appear in Phys. Rev.
Disorder-driven superconductor-normal metal phase transition in quasi-one-dimensional organic conductors
Effects of non-magnetic disorder on the critical temperature T_c and on
diamagnetism of quasi-one-dimensional superconductors are reported. The energy
of Josephson-coupling between wires is considered to be random, which is
typical for dirty organic superconductors. We show that this randomness
destroys phase coherence between wires and that T_c vanishes discontinuously at
a critical disorder-strength. The parallel and transverse components of the
penetration-depth are evaluated. They diverge at different critical
temperatures T_c^{(1)} and T_c, which correspond to pair-breaking and
phase-coherence breaking respectively. The interplay between disorder and
quantum phase fluctuations is shown to result in quantum critical behavior at
T=0, which manifests itself as a superconducting-normal metal phase transition
of first-order at a critical disorder strength.Comment: 12 pages, 3 figure
Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3
In the Peierls state very thin samples of TaS_3 (cross-section area \sim
10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the
threshold field. With approaching the Peierls transition temperature, T_P, the
smearing evolves into smooth growth of conductance from zero voltage
interpreted by us as the contribution of fluctuations to the non--linear
conductance. We identify independently the fluctuation contribution to the
linear conductance near T_P. Both linear and non-linear contributions depend on
temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently
reveal the same process. We reject creep of the {\it continuous} charge-density
waves (CDWs) as the origin of this effect and show that it is spontaneous phase
slippage that results in creep of the CDW. A model is proposed accounting for
both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR
Periodic sequences of arbitrage: a tale of four currencies
This paper investigates arbitrage chains involving four currencies and four foreign exchange trader‐arbitrageurs. In contrast with the three‐currency case, we find that arbitrage operations when four currencies are present may appear periodic in nature, and not involve smooth convergence to a ‘balanced’ ensemble of exchange rates in which the law of one price holds. The goal of this article is to understand some interesting features of sequences of arbitrage operations, features which might well be relevant in other contexts in finance and economics
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