Experimental Evidence for Anisotropic Double-Gap Behavior in M g B 2Cubitt, R; Levett, S
doi: 10.1103/PhysRevLett.90.157002pmid: 12732063
The behavior of a type II superconductor in the presence of a magnetic field is governed by two characteristic length scales, the London penetration depth and the coherence length. We present magnetization measurements on M g B 2 powder showing an anisotropy in the upper critical field and hence the coherence length of 6. Using the technique of small angle neutron scattering we show that this anisotropy is not mirrored in the London penetration depth, which is almost isotropic. This result can be explained by the superconductivity residing in two distinct electronic bands of the material, only one of which is highly anisotropic.
Eavesdropping on the “Ping-Pong” Quantum Communication ProtocolWójcik, Antoni
doi: 10.1103/PhysRevLett.90.157901pmid: 12732070
Security of the “ping-pong” quantum communication protocol recently proposed by Boström and Felbinger Phys. Rev. Lett. 89 , 187902 ( 2002 ) is analyzed in the case of considerable quantum channel losses. The eavesdropping scheme is presented, which reveals that the ping-pong protocol is not secure for transmission efficiencies lower than 60%. Our scheme induces 50% losses, which, however, can be hidden in the channel losses if one replaces the original lossy channel with a less lossy one. Finally, a possible improvement of the ping-pong protocol security is proposed.
Ultrahot Electron Formation under Excess Electron Drift through Solid XeUsenko, A; Frossati, G
doi: 10.1103/PhysRevLett.90.153201pmid: 12732035
The formation of “hot” (8 eV) electrons under excess electron drift in a moderate electrostatic field through solid xenon has been experimentally proved by observation of secondary electrons emitted from the photocathode. At T = 77 K and U = 1000 V one drifting electron produces about 20 (172 nm) photons, the efficiency of electric field–to–vacuum ultraviolet emission conversion is 15% tending to grow with temperature. A self-sustained electric discharge has been generated in solid Xe using a three-electrode cell with a zinc cathode.
Definition and Properties of Ideal Amorphous SolidsStachurski, Zbigniew H
doi: 10.1103/PhysRevLett.90.155502pmid: 12732045
It is proposed that two ideal amorphous structures, type I and type II, based on maximally random jammed packing of spheres of equal size, form a distinct class of ideal amorphous solids. The ideal amorphous structures contain wide variations in local density, limited by the condition of solidity. Four distinct characteristics, based on statistical geometry and topology, are shown to define this class. Voronoi tessellations carried out on simulated cells of random packed spheres and amorphous polymers give a broad distribution of individual volumes, skewed, with a tail at the high volume end.
Inflationary Spacetimes Are Incomplete in Past DirectionsBorde, Arvind ; Guth, Alan H; Vilenkin, Alexander H
doi: 10.1103/PhysRevLett.90.151301pmid: 12732026
Many inflating spacetimes are likely to violate the weak energy condition, a key assumption of singularity theorems. Here we offer a simple kinematical argument, requiring no energy condition, that a cosmological model which is inflating—or just expanding sufficiently fast—must be incomplete in null and timelike past directions. Specifically, we obtain a bound on the integral of the Hubble parameter over a past-directed timelike or null geodesic. Thus inflationary models require physics other than inflation to describe the past boundary of the inflating region of spacetime.
Anomalous Resistivity Resulting from MeV-Electron Transport in Overdense PlasmaSentoku, Y; Mima, K; Kaw, P; Nishikawa, K
doi: 10.1103/PhysRevLett.90.155001pmid: 12732040
Laser produced hot electron transport in an overdense plasma is studied by three-dimensional particle-in-cell simulations. Hot electron currents into the plasma generate neutralizing return currents in the cold plasma electrons, leading to a configuration which is unstable to electromagnetic Weibel and tearing instabilities. The resulting current filaments self-organize through a coalescence process finally settling into a single global current channel. The plasma return current experiences a strong anomalous resistivity due to diffusive flow of cold electrons in the magnetic perturbations. The resulting electrostatic field leads to an anomalously rapid stopping of fast MeV electrons (almost 3 orders of magnitude stronger than that through classical collisional effects).