400 research outputs found
Quantum entanglement in strong-field ionization
We investigate the time-evolution of quantum entanglement between an
electron, liberated by a strong few-cycle laser pulse, and its parent ion-core.
Since the standard procedure is numerically prohibitive in this case, we
propose a novel way to quantify the quantum correlation in such a system: we
use the reduced density matrices of the directional subspaces along the
polarization of the laser pulse and along the transverse directions as building
blocks for an approximate entanglement entropy. We present our results, based
on accurate numerical simulations, in terms of several of these entropies, for
selected values of the peak electric field strength and the carrier-envelope
phase difference of the laser pulse. The time evolution of the mutual entropy
of the electron and the ion-core motion along the direction of the laser
polarization is similar to our earlier results based on a simple
one-dimensional model. However, taking into account also the dynamics
perpendicular to the laser polarization reveals a surprisingly different
entanglement dynamics above the laser intensity range corresponding to pure
tunneling: the quantum entanglement decreases with time in the over-the-barrier
ionization regime
Search for Magnetic Field Induced Gap in a High-Tc Superconductor
Break junctions made of the optimally doped high temperature superconductor
Bi2Sr2Ca2CuO8 with Tc of 90 K has been investigated in magnetic fields up to 12
T, at temperatures from 4.2 K to Tc. The junction resistance varied between
1kOhm and 300kOhm. The differential conductance at low biases did not exhibit a
significant magnetic field dependence, indicating that a magnetic-field-induced
gap (Krishana et al., Science 277 83 (1997)), if exists, must be smaller than
0.25 meV.Comment: 3 pages, 2 figure
Magnetic-field-induced transition in BaVS3
The metal-insulator transition (MIT) of BaVS3 is suppressed under pressure
and above the critical pressure of p~2GPa the metallic phase is stabilized. We
present the results of detailed magnetoresistivity measurements carried out at
pressures near the critical value, in magnetic fields up to B=12T. We found
that slightly below the critical pressure the structural tetramerization --
which drives the MIT -- is combined with the onset of magnetic correlations. If
the zero-field transition temperature is suppressed to a sufficiently low value
(T_MI<15K), the system can be driven into the metallic state by application of
magnetic field. The main effect is not the reduction of T_MI with increasing B,
but rather the broadening of the transition due to the applied magnetic field.
We tentatively ascribe this phenomenon to the influence on the magnetic
structure coupled to the bond-order of the tetramers.Comment: 5 pages, 5 figure
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