1,650 research outputs found
Kramers polarization in strongly correlated carbon nanotube quantum dots
Ferromagnetic contacts put in proximity with carbon nanotubes induce spin and
orbital polarizations. These polarizations affect dramatically the Kondo
correlations occurring in quantum dots formed in a carbon nanotube, inducing
effective fields in both spin and orbital sectors. As a consequence, the carbon
nanotube quantum dot spectral density shows a four-fold split SU(4) Kondo
resonance. Furthermore, the presence of spin-orbit interactions leads to the
occurrence of an additional polarization among time-reversal electronic states
(polarization in the time-reversal symmetry or Kramers sector). Here, we
estimate the magnitude for the Kramer polarization in realistic carbon nanotube
samples and find that its contribution is comparable to the spin and orbital
polarizations. The Kramers polarization generates a new type of effective field
that affects only the time-reversal electronic states. We report new splittings
of the Kondo resonance in the dot spectral density which can be understood only
if Kramers polarization is taken into account. Importantly, we predict that the
existence of Kramers polarization can be experimentally detected by performing
nonlinear differential conductance measurements. We also find that, due to the
high symmetry required to build SU(4) Kondo correlations, its restoration by
applying an external field is not possible in contrast to the compensated SU(2)
Kondo state observed in conventional quantum dots.Comment: 8 pages, 4figure
Relativistic global and local divergences in hydrogenic systems: A study in position and momentum spaces
Relativistic effects in one-particle densities of hydrogenic systems are quantified by means of global and local density functionals: the Jensen-Shannon and the Jensen-Fisher divergences, respectively. The Schrödinger and Dirac radial densities are compared, providing complementary results in position and momentum spaces. While the electron cloud gets compressed towards the origin in the Dirac case, the momentum density spreads out over its domain, and the raising of minima in position space does not occur in the momentum space. Regarding the dependence on the nuclear charge and the state quantum numbers for all divergences here considered, as well as their mutual interconnection, accurate powerlike laws y˜Cxa are found systematically. The parameters {C,a} defining the respective dependences are extremely sensitive to the closeness of the system to the ground and/or the circular state. Particularly interesting are the analyses of (i) the plane subtended by the Jensen-Shannon and Jensen-Fisher divergences, in a given space (position or momentum), and (ii) either of the above two divergences in the position-momentum plane. These kinds of results show the complementary role of global and local divergences and that of both conjugate spaces
Cotunneling drag effect in Coulomb-coupled quantum dots
In Coulomb drag, a current flowing in one conductor can induce a voltage
across an adjacent conductor via the Coulomb interaction. The mechanisms
yielding drag effects are not always understood, even though drag effects are
sufficiently general to be seen in many low-dimensional systems. In this
Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot
(CC-DQD) and, through both experimental and theoretical arguments, identify
cotunneling as essential to obtaining a correct qualitative understanding of
the drag behavior.Comment: Main text: 5 pages, 5 figures; SM: 11 pages, 5 figures, 1 tabl
Complexity analysis of Klein-Gordon single-particle systems
The Fisher-Shannon complexity is used to quantitatively estimate the
contribution of relativistic effects to on the internal disorder of
Klein-Gordon single-particle Coulomb systems which is manifest in the rich
variety of three-dimensional geometries of its corresponding quantum-mechanical
probability density. It is observed that, contrary to the non-relativistic
case, the Fisher-Shannon complexity of these relativistic systems does depend
on the potential strength (nuclear charge). This is numerically illustrated for
pionic atoms. Moreover, its variation with the quantum numbers (n, l, m) is
analysed in various ground and excited states. It is found that the
relativistic effects enhance when n and/or l are decreasing.Comment: 4 pages, 3 figures, Accepted in EPL (Europhysics Letters
Information measures of hydrogenic systems, Laguerre polynomials and spherical harmonics
AbstractFisher's information and Shannon's entropy are two complementary information measures of a probability distribution. Here, the probability distributions which characterize the quantum-mechanical states of a hydrogenic system are analyzed by means of these two quantities. These distributions are described in terms of Laguerre polynomials and spherical harmonics, whose characteristics are controlled by the three integer quantum numbers of the corresponding states. We have found the explicit expression for the Fisher information, and a lower bound for the Shannon entropy with the help of an isoperimetric inequality
Casimir Force for Absorbing Media in an Open Quantum System Framework: Scalar Model
In this article we compute the Casimir force between two finite-width mirrors
at finite temperature, working in a simplified model in 1+1 dimensions. The
mirrors, considered as dissipative media, are modeled by a continuous set of
harmonic oscillators which in turn are coupled to an external environment at
thermal equilibrium. The calculation of the Casimir force is performed in the
framework of the theory of quantum open systems. It is shown that the Casimir
interaction has two different contributions: the usual radiation pressure from
vacuum, which is obtained for ideal mirrors without dissipation or losses, and
a Langevin force associated with the noise induced by the interaction between
dielectric atoms in the slabs and the thermal bath. Both contributions to the
Casimir force are needed in order to reproduce the analogous of Lifshitz
formula in 1+1 dimensions. We also discuss the relation between the
electromagnetic properties of the mirrors and the spectral density of the
environmentComment: Minor changes, version to appear in Phys. Rev.
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