15 research outputs found
Interplay between Josephson effect and magnetic interactions in double quantum dots
We analyze the magnetic and transport properties of a double quantum dot
coupled to superconducting leads. In addition to the possible phase transition
to a state, already present in the single dot case, this system exhibits
a richer magnetic behavior due to the competition between Kondo and inter-dot
antiferromagnetic coupling. We obtain results for the Josephson current which
may help to understand recent experiments on superconductor-metallofullerene
dimer junctions. We show that in such a system the Josephson effect can be used
to control its magnetic configuration.Comment: 5 pages, 4 figure
Equivalent bosonic theory for the massive Thirring model with non-local interaction
We study, through path-integral methods, an extension of the massive Thirring
model in which the interaction between currents is non-local. By examining the
mass-expansion of the partition function we show that this non-local massive
Thirring model is equivalent to a certain non-local extension of the
sine-Gordon theory. Thus, we establish a non-local generalization of the famous
Coleman's equivalence. We also discuss some possible applications of this
result in the context of one-dimensional strongly correlated systems and
finite-size Quantum Field Theories.Comment: 15 pages, latex, no figure
Resonant hyper-Raman scattering in spherical quantum dots
A theoretical model of resonant hyper-Raman scattering by an ensemble of
spherical semiconductor quantum dots has been developed. The electronic
intermediate states are described as Wannier-Mott excitons in the framework of
the envelope function approximation. The optical polar vibrational modes of the
nanocrystallites (vibrons) and their interaction with the electronic system are
analized with the help of a continuum model satisfying both the mechanical and
electrostatic matching conditions at the interface. An explicit expression for
the hyper-Raman scattering efficiency is derived, which is valid for incident
two-photon energy close to the exciton resonances. The dipole selection rules
for optical transitions and Fr\"ohlich-like exciton-lattice interaction are
derived: It is shown that only exciton states with total angular momentum
and vibrational modes with angular momentum contribute to the
hyper-Raman scattering process. The associated exciton energies, wavefunctions,
and vibron frequencies have been obtained for spherical CdSe zincblende-type
nanocrystals, and the corresponding hyper-Raman scattering spectrum and
resonance profile are calculated. Their dependence on the dot radius and the
influence of the size distribution on them are also discussed.Comment: 12 pages REVTeX (two columns), 2 tables, 8 figure
Probing Supergravity Models with Indirect Experimental Signatures
We explore the one-loop electroweak radiative corrections in the context of
the traditional minimal and the string-inspired
supergravity models by calculating explicitly vacuum-polarization and
vertex-correction contributions to the and
parameters. We also include in this analysis the constraint from whose inclusive branching ratio has been
actually measured very recently by CLEO. We find that by combining these three
most important indirect experimental signatures and using the most recent
experimental values for them, is excluded for
in both the minimal supergravity and the no-scale supergravity. We also find that is
excluded for any sign of in the minimal () supergravity
model.Comment: RevTeX 3.0, 16 Pages+4 figures(not included but available as a
uuencoded file from [email protected]), SNUTP-94-9
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
Charge and Spin Effects in Mesoscopic Josephson Junctions
We consider the charge and spin effects in low dimensional superconducting
weak links. The first part of the review deals with the effects of
electron-electron interaction in Superconductor/Luttinger liquid/Superconductor
junctions. The experimental realization of this mesoscopic hybrid system can be
the individual single wall carbon nanotube that bridges the gap between two
bulk superconductors. The dc Josephson current through a Luttinger liquid in
the limits of perfectly and poorly transmitting junctions is evaluated. The
relationship between the Josephson effect in a long SNS junction and the
Casimir effect is discussed. In the second part of the paper we review the
recent results concerning the influence of the Zeeman and Rashba interactions
on the thermodynamical properties of ballistic S/QW/S junction fabricated in
two dimensional electron gas. It is shown that in magnetically controlled
junction there are conditions for resonant Cooper pair transition which results
in giant supercurrent through a tunnel junction and a giant magnetic response
of a multichannel SNS junction. The supercurrent induced by the joint action of
the Zeeman and Rashba interactions in 1D quantum wires connected to bulk
superconductors is predicted.Comment: 36 pages, 8 figures; minor changes in reference
Study of Constrained Minimal Supersymmetry
Taking seriously phenomenological indications for supersymmetry, we have made
a detailed study of unified minimal SUSY, including effects at the few percent
level in a consistent fashion. We report here a general analysis without
choosing a particular unification gauge group. We find that the encouraging
SUSY unification results of recent years do survive the challenge of a more
complete and accurate analysis. Taking into account effects at the 5-10% level
leads to several improvements of previous results, and allows us to sharpen our
predictions for SUSY in the light of unification. We perform a thorough study
of the parameter space. The results form a well-defined basis for comparing the
physics potential of different facilities. Very little of the acceptable
parameter space has been excluded by LEP or FNAL so far, but a significant
fraction can be covered when these accelerators are upgraded. A number of
initial applications to the understanding of the SUSY spectrum, detectability
of SUSY at LEP II or FNAL, BR(), Width(), dark
matter, etc, are included in a separate section. We formulate an approach to
extracting SUSY parameters from data when superpartners are detected. For small
tan(beta) or large both and are entirely bounded from
above at O(1 tev) without having to use a fine-tuning constraint.Comment: Michigan preprint UM-TH-93-24, LaTeX, 60 pages without figures.
Complete paper with inline figures available by anonymous ftp to
williams.physics.lsa.umich.edu in /pub/preprints/UM-TH-93-24.ps.Z
(uncompresses to 10MB / 77 pages), or by e-mailing reques