133,970 research outputs found
Field-ionization threshold and its induced ionization-window phenomenon for Rydberg atoms in a short single-cycle pulse
We study the field-ionization threshold behavior when a Rydberg atom is
ionized by a short single-cycle pulse field. Both hydrogen and sodium atoms are
considered. The required threshold field amplitude is found to scale
\emph{inversely} with the binding energy when the pulse duration becomes
shorter than the classical Rydberg period, and, thus, more weakly bound
electrons require larger fields for ionization. This threshold scaling behavior
is confirmed by both 3D classical trajectory Monte Carlo simulations and
numerically solving the time-dependent Schr\"{o}dinger equation. More
surprisingly, the same scaling behavior in the short pulse limit is also
followed by the ionization thresholds for much lower bound states, including
the hydrogen ground state. An empirical formula is obtained from a simple
model, and the dominant ionization mechanism is identified as a nonzero spatial
displacement of the electron. This displacement ionization should be another
important mechanism beyond the tunneling ionization and the multiphoton
ionization. In addition, an "ionization window" is shown to exist for the
ionization of Rydberg states, which may have potential applications to
selectively modify and control the Rydberg-state population of atoms and
molecules
Temperature dependence of electron-phonon interactions in vanadium
First-principles calculations were used to study the Fermi surface of body-centered cubic vanadium at elevated temperatures. Supercell calculations accounted for effects of thermal atom displacements on band energies, and band unfolding was used to project the spectral weight of the electron states into the Brillouin zone of a standard bcc unit cell. An electronic topological transition (ETT, or Lifshitz transition) occurred near the Γ point with increasing temperature, but the large thermal smearings from the atomic disorder and the Fermi-Dirac distribution reduced the effect of this ETT on the electron-phonon interactions. The phonon dispersions showed thermal stiffening of their Kohn anomalies near the Γ point and of the longitudinal N phonon mode. In general the effects of the ETT were overcome by the thermal smearing of the Fermi surface that reduces the spanning vector densities for anomalous phonon modes
GAPS IN THE HEISENBERG-ISING MODEL
We report on the closing of gaps in the ground state of the critical
Heisenberg-Ising chain at momentum . For half-filling, the gap closes at
special values of the anisotropy , integer. We explain
this behavior with the help of the Bethe Ansatz and show that the gap scales as
a power of the system size with variable exponent depending on . We use
a finite-size analysis to calculate this exponent in the critical region,
supplemented by perturbation theory at . For rational
fillings, the gap is shown to be closed for {\em all} values of and
the corresponding perturbation expansion in shows a remarkable
cancellation of various diagrams.Comment: 12 RevTeX pages + 4 figures upon reques
Spinless Calogero-Sutherland model with twisted boundary condition
In this work, the spinless Calogero-Sutherland model with twisted boundary
condition is studied. The ground state wavefunctions, the ground state
energies, the full energy spectrum are provided in details.Comment: preprint of ETH-L, appearing in recent PR
Tunneling, dissipation, and superfluid transition in quantum Hall bilayers
We study bilayer quantum Hall systems at total Landau level filling factor
in the presence of interlayer tunneling and coupling to a dissipative
normal fluid. Describing the dynamics of the interlayer phase by an effective
quantum dissipative XY model, we show that there exists a critical dissipation
set by the conductance of the normal fluid. For ,
interlayer tunnel splitting drives the system to a quantum Hall state.
For , interlayer tunneling is irrelevant at low temperatures,
the system exhibits a superfluid transition to a collective quantum Hall state
supported by spontaneous interlayer phase coherence. The resulting phase
structure and the behavior of the in-plane and tunneling currents are studied
in connection to experiments.Comment: 4 RevTex pages, revised version, to appear in Phys. Rev. Let
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