61,035 research outputs found
Dynamics of multiply charged ions in intense laser fields
We numerically investigate the dynamics of multiply charged hydrogenic ions
in near-optical linearly polarized laser fields with intensities of order 10^16
to 10^17 W/cm^2. Depending on the charge state Z of the ion the relation of
strength between laser field and ionic core changes. We find around Z=12
typical multiphoton dynamics and for Z=3 tunneling behaviour, however with
clear relativistic signatures. In first order in v/c the magnetic field
component of the laser field induces a Z-dependent drift in the laser
propagation direction and a substantial Z-dependent angular momentum with
repect to the ionic core. While spin oscillations occur already in first order
in v/c as described by the Pauli equation, spin induced forces via spin orbit
coupling only appear in the parameter regime where (v/c)^2 corrections are
significant. In this regime for Z=12 ions we show strong splittings of resonant
spectral lines due to spin-orbit coupling and substantial corrections to the
conventional Stark shift due to the relativistic mass shift while those to the
Darwin term are shown to be small. For smaller charges or higher laser
intensities, parts of the electronic wavepacket may tunnel through the
potential barrier of the ionic core, and when recombining are shown to give
rise to keV harmonics in the radiation spectrum. Some parts of the wavepacket
do not recombine after ionisation and we find very energetic electrons in the
weakly relativistic regime of above threshold ionization.Comment: submitte
Numerical Study of Universal Conductance Fluctuation in Three-dimensional Topological Semimetals
We study the conductance fluctuation in topological semimetals. Through
statistic distribution of energy levels of topological semimetals, we determine
the dominant parameters of universal conductance fluctuation (UCF), i.e., the
number of uncorrelated bands , the level degeneracy , and the symmetry
parameter . These parameters allow us to predict the zero-temperature
intrinsic UCF of topological semimetals by the Altshuler-Lee-Stone theory.
Then, we obtain numerically the conductance fluctuations for topological
semimetals of quasi-1D geometry. We find that for Dirac/Weyl semimetals, the
theoretical prediction coincides with the numerical results. However, a
non-universal conductance fluctuation behavior is found for topological nodal
line semimetals, i.e., the conductance fluctuation amplitude increases with the
enlargement of SOC strength. We find that such unexpected parameter-dependent
phenomena of conductance fluctuation are related to Fermi surface shape of 3D
topological semimetals. These results will help us to understand the existing
and future experimental results of UCF in 3D topological semimetals.Comment: 9 pages, 8 figure
Coherent population trapping in a dressed two-level atom via a bichromatic field
We show theoretically that by applying a bichromatic electromagnetic field,
the dressed states of a monochromatically driven two-level atom can be pumped
into a coherent superposition termed as dressed-state coherent population
trapping. Such effect can be viewed as a new doorknob to manipulate a two-level
system via its control over dressed-state populations. Application of this
effect in the precision measurement of Rabi frequency, the unexpected
population inversion and lasing without inversion are discussed to demonstrate
such controllability.Comment: 14 pages, 6 figure
Particle-continuum-medium duality of skyrmions
Topological solitons are crucial to many branches of physics, such as models
of fundamental particles in quantum field theory, information carriers in
nonlinear optics, and elementary entities in quantum and classical
computations. Chiral magnetic materials are a fertile ground for studying
solitons. In the past a few years, a huge number of all kinds of topologically
protected localized magnetic solitons have been found. The number is so large,
and a proper organization and classification is necessary for their future
developments. Here we show that many topological magnetic solitons can be
understood from the duality of particle and elastic continuum-medium nature of
skyrmions. In contrast to the common belief that a skyrmion is an elementary
particle that is indivisible, skyrmions behave like both particle and continuum
media that can be tore apart to bury other objects, reminiscing particle-wave
duality in quantum mechanics. Skyrmions, like indivisible particles, can be
building blocks for cascade skyrmion bags and target skyrmions. They can also
act as bags and glues to hold one or more skyrmions together. The principles
and rules for stable composite skyrmions are explained and presented, revealing
their rich and interesting physics.Comment: 14 pages, 8 figure
Bicritical and tetracritical phenomena and scaling properties of the SO(5) theory
By large scale Monte Carlo simulations it is shown that the stable fixed
point of the SO(5) theory is either bicritical or tetracritical depending on
the effective interaction between the antiferromagnetism and superconductivity
orders. There are no fluctuation-induced first-order transitions suggested by
epsilon expansions. Bicritical and tetracritical scaling functions are derived
for the first time and critical exponents are evaluated with high accuracy.
Suggestions on experiments are given.Comment: 11 pages, 8 postscript figures, Revtex, revised versio
Analytical Solution of Electron Spin Decoherence Through Hyperfine Interaction in a Quantum Dot
We analytically solve the {\it Non-Markovian} single electron spin dynamics
due to hyperfine interaction with surrounding nuclei in a quantum dot. We use
the equation-of-motion method assisted with a large field expansion, and find
that virtual nuclear spin flip-flops mediated by the electron contribute
significantly to a complete decoherence of transverse electron spin correlation
function. Our results show that a 90% nuclear polarization can enhance the
electron spin time by almost two orders of magnitude. In the long time
limit, the electron spin correlation function has a non-exponential
decay in the presence of both polarized and unpolarized nuclei.Comment: 4 pages, 3 figure
Instabilities at [110] Surfaces of d_{x^2-y^2} Superconductors
We compare different scenarios for the low temperature splitting of the
zero-energy peak in the local density of states at (110) surfaces of
d_{x^2-y^2}-wave superconductors, observed by Covington et al.
(Phys.Rev.Lett.79 (1997), 277). Using a tight binding model in the
Bogolyubov-de Gennes treatment we find a surface phase transition towards a
time-reversal symmetry breaking surface state carrying spontaneous currents and
an s+id-wave state. Alternatively, we show that electron correlation leads to a
surface phase transition towards a magnetic state corresponding to a local spin
density wave state.Comment: 4 pages, 5 figure
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