33,832 research outputs found
Spin Fluctuation Induced Dephasing in a Mesoscopic Ring
We investigate the persistent current in a hybrid Aharonov-Bohm ring -
quantum dot system coupled to a reservoir which provides spin fluctuations. It
is shown that the spin exchange interaction between the quantum dot and the
reservoir induces dephasing in the absence of direct charge transfer. We
demonstrate an anomalous nature of this spin-fluctuation induced dephasing
which tends to enhance the persistent current. We explain our result in terms
of the separation of the spin from the charge degree of freedom. The nature of
the spin fluctuation induced dephasing is analyzed in detail.Comment: 4 pages, 4 figure
Electronic structure of YbB: Is it a Topological Insulator or not?
To resolve the controversial issue of the topological nature of the
electronic structure of YbB, we have made a combined study using density
functional theory (DFT) and angle resolved photoemission spectroscopy (ARPES).
Accurate determination of the low energy band topology in DFT requires the use
of modified Becke-Johnson exchange potential incorporating the spin-orbit
coupling and the on-site Coulomb interaction of Yb electrons as large
as 7 eV. We have double-checked the DFT result with the more precise GW band
calculation. ARPES is done with the non-polar (110) surface termination to
avoid band bending and quantum well confinement that have confused ARPES
spectra taken on the polar (001) surface termination. Thereby we show
definitively that YbB has a topologically trivial B 2-Yb 5
semiconductor band gap, and hence is a non-Kondo non-topological insulator
(TI). In agreement with theory, ARPES shows pure divalency for Yb and a -
band gap of 0.3 eV, which clearly rules out both of the previous scenarios of
- band inversion Kondo TI and - band inversion non-Kondo TI. We
have also examined the pressure-dependent electronic structure of YbB,
and found that the high pressure phase is not a Kondo TI but a
\emph{p}-\emph{d} overlap semimetal.Comment: The main text is 6 pages with 4 figures, and the supplementary
information contains 6 figures. 11 pages, 10 figures in total To be appeared
in Phys. Rev. Lett. (Online publication is around March 16 if no delays.
Self-Doping of Gold Chains on Silicon: A New Structural Model for Si(111)5x2-Au
A new structural model for the Si(111)5x2-Au reconstruction is proposed and
analyzed using first-principles calculations. The basic model consists of a
"double honeycomb chain" decorated by Si adatoms. The 5x1 periodicity of the
honeycomb chains is doubled by the presence of a half-occupied row of Si atoms
that partially rebonds the chains. Additional adatoms supply electrons that
dope the parent band structure and stabilize the period doubling; the optimal
doping corresponds to one adatom per four 5x2 cells, in agreement with
experiment. All the main features observed in scanning tunneling microscopy and
photoemission are well reproduced.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Lett. (preprint with high
quality figures available at
http://cst-www.nrl.navy.mil/~erwin/papers/ausi111
Effect of Charge Fluctuations on the Persistent Current through a Quantum Dot
We study coherent charge transfer between an Aharonov-Bohm ring and a
side-attached quantum dot. The charge fluctuation between the two
sub-structures is shown to give rise to algebraic suppression of the persistent
current circulating the ring as the size of the ring becomes relatively large.
The charge fluctuation at resonance provides transition between the diamagnetic
and the paramagnetic states.
Universal scaling, crossover behavior of the persistent current from a
continuous to a discrete energy limit in the ring is also discussed.Comment: 5 pages, 4 figure
Current-induced dendritic magnetic instability in superconducting MgB2 films
Magneto-optical imaging reveals that in superconducting films of MgB2 a
transport current creates avalanche-like flux dynamics where highly branching
dendritic penetration patterns are formed. The instability is triggered when
the current exceeds a threshold value, and the superconductor, shaped as a long
strip, is initially in the critical state. The instability exists up to 19 K,
which is a much wider temperature range than in previous experiments, where
dendrites were formed by applying a magnetic field. The instability is believed
to be of thermo-magnetic origin indicating that thermal stabilization may
become crucial in applications of MgB2.Comment: 3 pages, 3 figures, resubmitted to Appl.Phys.Let
A Novel Method for the Solution of the Schroedinger Eq. in the Presence of Exchange Terms
In the Hartree-Fock approximation the Pauli exclusion principle leads to a
Schroedinger Eq. of an integro-differential form. We describe a new spectral
noniterative method (S-IEM), previously developed for solving the
Lippman-Schwinger integral equation with local potentials, which has now been
extended so as to include the exchange nonlocality. We apply it to the
restricted case of electron-Hydrogen scattering in which the bound electron
remains in the ground state and the incident electron has zero angular
momentum, and we compare the acuracy and economy of the new method to three
other methods. One is a non-iterative solution (NIEM) of the integral equation
as described by Sams and Kouri in 1969. Another is an iterative method
introduced by Kim and Udagawa in 1990 for nuclear physics applications, which
makes an expansion of the solution into an especially favorable basis obtained
by a method of moments. The third one is based on the Singular Value
Decomposition of the exchange term followed by iterations over the remainder.
The S-IEM method turns out to be more accurate by many orders of magnitude than
any of the other three methods described above for the same number of mesh
points.Comment: 29 pages, 4 figures, submitted to Phys. Rev.
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