3,673 research outputs found
Consistency Conditions of the Faddeev-Niemi-Periwal Ansatz for the SU(N) Gauge Field
The consistency condition of the Faddeev-Niemi ansatz for the gauge-fixed
massless SU(2) gauge field is discussed. The generality of the ansatz is
demonstrated by obtaining a sufficient condition for the existence of the
three-component field introduced by Faddeev and Niemi. It is also shown that
the consistency conditions determine this three-component field as a functional
of two arbitrary functions. The consistency conditions corresponding to the
Periwal ansatz for the SU(N) gauge field with N larger than 2 are also
obtained. It is shown that the gauge field obeying the Periwal ansatz must
satisfy extra (N-1)(N-2)/2 conditions.Comment: PTP Tex, 15 pages, Eq.(3.18) inserte
Non-Abelian Stokes Theorem for Loop Variables Associated with Nontrivial Loops
The non-Abelian Stokes theorem for loop variables associated with nontrivial
loops (knots and links) is derived. It is shown that a loop variable is in
general different from unity even if the field strength vanishes everywhere on
the surface surrounded by the loop.Comment: 18 pages,10 Postscript figures, PTP Tex, Journal-ref adde
Strain-driven light polarization switching in deep ultraviolet nitride emitters
Residual strain plays a critical role in determining the crystalline quality
of nitride epitaxial layers and in modifying their band structure; this often
leads to several interesting physical phenomena. It is found, for example, that
compressive strain in AlxGa1-xN layers grown on AlyGa1-yN (x<y) templates
results in an anti-crossing of the valence bands at considerably much higher Al
composition than expected. This happens even in the presence of large and
negative crystal field splitting energy for AlxGa1-xN layers. A judicious
magnitude of the compressive strain can support vertical light emission (out of
the c-plane) from AlxGa1-xN quantum wells up to x\approx 0.80, which is
desirable for the development of deep ultraviolet light-emitting diodes
designed to operate below 250nm with transverse electric polarization
characteristics
Landauer-B\"uttiker approach for hyperfine mediated electronic transport in the integer quantum Hall regime
The interplay of spin-polarized electronic edge states with the dynamics of
the host nuclei in quantum Hall systems presents rich and non-trivial transport
physics. Here, we develop a Landauer-B\"uttiker approach to understand various
experimental features observed in the integer quantum Hall set ups featuring
quantum point contacts. The approach developed here entails a phenomenological
description of spin resolved inter-edge scattering induced via hyperfine
assisted electron-nuclear spin flip-flop processes. A self-consistent
simulation framework between the nuclear spin dynamics and edge state
electronic transport is presented in order to gain crucial insights into the
dynamic nuclear polarization effects on electronic transport and in turn the
electron-spin polarization effects on the nuclear spin dynamics. In particular,
we show that the hysteresis noted experimentally in the conductance-voltage
trace as well as in the resistively detected NMR lineshape results from a lack
of quasi-equilibrium between electronic transport and nuclear polarization
evolution. In addition, we present circuit models to emulate such hyperfine
mediated transport effects to further facilitate a clear understanding of the
electronic transport processes occurring around the quantum point contact.
Finally, we extend our model to account for the effects of quadrupolar
splitting of nuclear levels and also depict the electronic transport signatures
that arise from single and multi-photon processes.Comment: 21 pages, 8 figure
A gate-defined silicon quantum dot molecule
We report electron transport measurements of a silicon double dot formed in
multi-gated metal-oxide-semiconductor structures with a 15-nm-thick
silicon-on-insulator layer. Tunable tunnel coupling enables us to observe an
excitation spectrum in weakly coupled dots and an energy level anticrossing in
strongly coupled ones. Such a quantum dot molecule with both charge and energy
quantization provides the essential prerequisite for future implementation of
silicon-based quantum computations.Comment: 11pages,3figure
Construction of a topological charge on fuzzy S^2 x S^2 via Ginsparg-Wilson relation
We construct a topological charge of gauge field configurations on a fuzzy
S^2xS^2 by using a Dirac operator satisfying the Ginsparg-Wilson relation. The
topological charge defined on the fuzzy S^2xS^2 can be interpreted as a
noncommutative (or matrix) generalization of the 2nd Chern character on
S^2xS^2. We further calculate the number of chiral zero modes of the Dirac
operator in topologically nontrivial gauge configurations. Generalizations of
our formulation to fuzzy (S^2)^k are also discussed.Comment: 30 pages, typo corrected, version published in Phys.Rev.
A Class of Exact Solutions of the Faddeev Model
A class of exact solutions of the Faddeev model, that is, the modified SO(3)
nonlinear sigma model with the Skyrme term, is obtained in the four dimensional
Minkowskian spacetime. The solutions are interpreted as the isothermal
coordinates of a Riemannian surface. One special solution of the static vortex
type is investigated numerically. It is also shown that the Faddeev model is
equivalent to the mesonic sector of the SU(2) Skyrme model where the baryon
number current vanishes.Comment: 20 pages, 7 figures, refs. adde
Coherent manipulation of electronic states in a double quantum dot
We investigate coherent time-evolution of charge states (pseudo-spin qubit)
in a semiconductor double quantum dot. This fully-tunable qubit is manipulated
with a high-speed voltage pulse that controls the energy and decoherence of the
system. Coherent oscillations of the qubit are observed for several
combinations of many-body ground and excited states of the quantum dots.
Possible decoherence mechanisms in the present device are also discussed.Comment: RevTe
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