87 research outputs found
Angular Conductance Resonances of Quantum Dots Non-Collinearly Coupled to Ferromagnetic Leads
The zero bias conductance of quantum dots coupled to ferromagnetic leads is
investigated. In the strong coupling regime, it is found that the conductance
is a non-monotonic function of the angle between the magnetisation directions
in the two contacts. This behaviour is an effect of the presence of the leads
which induces an angle dependent spin split of the quantum dot states, and spin
flip transitions between the quantum dot states whenever the magnetisation
directions of the leads are non-collinear which enhances the current density at
the chemical potential. In the weak coupling regime, the system reverts to
normal spin valve character.Comment: 4 pages, 4 figures. Europhysics Letters (accepted
Calculation of atomic spontaneous emission rate in 1D finite photonic crystal with defects
We derive the expression for spontaneous emission rate in finite
one-dimensional photonic crystal with arbitrary defects using the effective
resonator model to describe electromagnetic field distributions in the
structure. We obtain explicit formulas for contributions of different types of
modes, i.e. radiation, substrate and guided modes. Formal calculations are
illustrated with a few numerical examples, which demonstrate that the
application of effective resonator model simplifies interpretation of results.Comment: Cent. Eur. J. Phys, in pres
Relativistic, QED, and nuclear mass effects in the magnetic shielding of He
The magnetic shielding of He is studied. The complete
relativistic corrections of order , leading QED corrections of
order , and finite nuclear mass effects of order
are calculated with high numerical precision. The resulting
theoretical predictions for are the most
accurate to date among all elements and support the use of He as a NMR
standard.Comment: 10 pages, corrected minor errors in Eqs.(6,7
Transient heat generation in a quantum dot under a step-like pulse bias
We study the transient heat generation in a quantum dot system driven by a
step-like or a square-shaped pulse bias. We find that a periodically
oscillating heat generation arises after adding the sudden bias. One
particularly surprising result is that there exists a heat absorption from the
zero-temperature phonon subsystem. Thus the phonon population in
non-equilibrium can be less than that of the equilibrium electron-phonon
system. In addition, we also ascertain the optimal conditions for the operation
of a quantum dot with the minimum heat generation.Comment: 6 pages, 4 figure
Indium rich InGaN solar cells grown by MOCVD
This study focuses on both epitaxial growths of InxGa 1-xN epilayers with graded In content, and the performance of solar cells structures grown on sapphire substrate by using metal organic chemical vapor deposition. The high resolution X-ray and Hall Effect characterization were carried out after epitaxial InGaN solar cell structures growth. The In content of the graded InGaN layer was calculated from the X-ray reciprocal space mapping measurements. Indium contents of the graded InGaN epilayers change from 8.8 to 7.1 % in Sample A, 15.7-7.1 % in Sample B, and 26.6-15.1 % in Sample C. The current voltage measurements of the solar cell devices were carried out after a standard micro fabrication procedure. Sample B exhibits better performance with a short-circuit current density of 6 mA/cm2, open-circuit voltage of 0.25 V, fill factor of 39.13 %, and the best efficiency measured under a standard solar simulator with one-sun air mass 1.5 global light sources (100 mW/cm2) at room temperature for finished devices was 0.66 %. © 2014 Springer Science+Business Media New York
Spintronic transport and Kondo effect in quantum dots
We investigate the spin-dependent transport properties of quantum-dot based
structures where Kondo correlations dominate the electronic dynamics. The
coupling to ferromagnetic leads with parallel magnetizations is known to give
rise to nontrivial effects in the local density of states of a single quantum
dot. We show that this influence strongly depends on whether charge
fluctuations are present or absent in the dot. This result is confirmed with
numerical renormalization group calculations and perturbation theory in the
on-site interaction. In the Fermi-liquid fixed point, we determine the
correlations of the electric current at zero temperature (shot noise) and
demonstrate that the Fano factor is suppressed below the Poissonian limit for
the symmetric point of the Anderson Hamiltonian even for nonzero lead
magnetizations. We discuss possible avenues of future research in this field:
coupling to the low energy excitations of the ferromagnets (magnons), extension
to double quantum dot systems with interdot antiferromagnetic interaction and
effect of spin-polarized currents on higher symmetry Kondo states such as
SU(4).Comment: 11 pages, 5 figures. Proceedings of the 3rd Intl. Conf. on Physics
and Applications of Spin-Related Phenomena in Semiconductors, Santa Barbara,
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