11,982 research outputs found
Effective tuning of exciton polarization splitting in coupled quantum dots
The polarization splitting of the exciton ground state in two laterally
coupled quantum dots under an in-plane electric field is investigated and its
effective tuning is designed. It is found that there are significant Stark
effect and anticrossing in energy levels. Due to coupling between inter- and
intra-dot states, the absolute value of polarization splitting is significantly
reduced, and it could be tuned to zero by the electric field for proper
inter-dot separations. Our scheme is interesting for the research on the
quantum dots-based entangled-photon source.Comment: 4 pages, 2 figures, to appear in Appl. Phys. Let
Effects of arbitrarily directed field on spin phase oscillations in biaxial molecular magnets
Quantum phase interference and spin-parity effects are studied in biaxial
molecular magnets in a magnetic field at an arbitrarily directed angle. The
calculations of the ground-state tunnel splitting are performed on the basis of
the instanton technique in the spin-coherent-state path-integral
representation, and complemented by exactly numerical diagonalization. Both the
Wentzel-Kramers-Brillouin exponent and the preexponential factor are obtained
for the entire region of the direction of the field. Our results show that the
tunnel splitting oscillates with the field for the small field angle, while for
the large field angle the oscillation is completely suppressed. This distinct
angular dependence, together with the dependence of the tunnel splitting on the
field strengh, provide an independent test for spin-parity effects in biaxial
molecular magnets. The analytical results for the molecular Fe magnet,
are found to be in good areement with the numerical simulations, which suggests
that even the molecular magnet with total spin S=10 is large enough to be
treated as a giant spin system.Comment: 19 pages, 5 figure
Spin tunneling properties in mesoscopic magnets: effects of a magnetic field
The tunneling of a giant spin at excited levels is studied theoretically in
mesoscopic magnets with a magnetic field at an arbitrary angle in the easy
plane. Different structures of the tunneling barriers can be generated by the
magnetocrystalline anisotropy, the magnitude and the orientation of the field.
By calculating the nonvacuum instanton solution explicitly, we obtain the
tunnel splittings and the tunneling rates for different angle ranges of the
external magnetic field ( and ). The
temperature dependences of the decay rates are clearly shown for each case. It
is found that the tunneling rate and the crossover temperature depend on the
orientation of the external magnetic field. This feature can be tested with the
use of existing experimental techniques.Comment: 27 pages, 4 figures, accepted by Euro. Phys. J.
Field-dependent quantum nucleation of antiferromagnetic bubbles
The phenomenon of quantum nucleation is studied in a nanometer-scale
antiferromagnet with biaxial symmetry in the presence of a magnetic field at an
arbitrary angle. Within the instanton approach, we calculate the dependence of
the rate of quantum nucleation and the crossover temperature on the orientation
and strength of the field for bulk solids and two-dimensional films of
antiferromagnets, respectively. Our results show that the rate of quantum
nucleation and the crossover temperature from thermal-to-quantum transitions
depend on the orientation and strength of the field distinctly, which can be
tested with the use of existing experimental techniques.Comment: 21 pages, 5 figures, Final version and accepted by Eur. Phys. J
Low energy exciton states in a nanoscopic semiconducting ring
We consider an effective mass model for an electron-hole pair in a simplified
confinement potential, which is applicable to both a nanoscopic self-assembled
semiconducting InAs ring and a quantum dot. The linear optical susceptibility,
proportional to the absorption intensity of near-infrared transmission, is
calculated as a function of the ring radius . Compared with the
properties of the quantum dot corresponding to the model with a very small
radius , our results are in qualitative agreement with the recent
experimental measurements by Pettersson {\it et al}.Comment: 4 pages, 4 figures, revised and accepted by Phys. Rev.
Spin-dependent Rotating Wigner Molecules in Quantum dots
The spin-dependent trial wave functions with rotational symmetry are
introduced to describe rotating Wigner molecular states with spin degree of
freedom in four- and five-electron quantum dots under magnetic fields. The
functions are constructed with unrestricted Hartree-Fock orbits and projection
technique in long-range interaction limit. They highly overlap with the
exact-diagonalized ones and give the accurate energies in strong fields. The
zero points, i.e. vortices of the functions have straightforward relations to
the angular momenta of the states. The functions with different total spins
automatically satisfy the angular momentum transition rules with the increase
of magnetic fields and explicitly show magnetic couplings and characteristic
oscillations with respect to the angular momenta. Based on the functions, it is
demonstrated that the entanglement entropies of electrons depend on the
z-component of total spin and rise with the increase of angular momenta
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