29,639 research outputs found
Fabrication of nanometer-spaced electrodes using gold nanoparticles
A simple and highly reproducible technique is demonstrated for the
fabrication of metallic electrodes with nanometer separation. Commercially
available bare gold colloidal nanoparticles are first trapped between
prefabricated large-separation electrodes to form a low-resistance bridge by an
ac electric field. A large dc voltage is then applied to break the bridge via
electromigration at room temperature, which consistently produces gaps in the
sub-10 nm range. The technique is readily applied to prefabricated electrodes
with separation up to 1 micron, which can be defined using optical lithography.
The simple fabrication scheme will facilitate electronic transport studies of
individual nanostructures made by chemical synthesis. As an example,
measurement of a thiol-coated gold nanoparticle showing a clear Coulomb
staircase is presented.Comment: To appear in Appl. Phys. Lett. in Dec. 200
Q-operator and T-Q relation from the fusion hierarchy
We propose that the Baxter -operator for the spin-1/2 XXZ quantum spin
chain is given by the limit of the transfer matrix with spin-
(i.e., -dimensional) auxiliary space. Applying this observation to the
open chain with general (nondiagonal) integrable boundary terms, we obtain from
the fusion hierarchy the - relation for {\it generic} values (i.e. not
roots of unity) of the bulk anisotropy parameter. We use this relation to
determine the Bethe Ansatz solution of the eigenvalues of the fundamental
transfer matrix. This approach is complementary to the one used recently to
solve the same model for the roots of unity case.Comment: Latex file, 12 pages; V2, misprints corrected and references adde
Theoretical overview on tau physics
Precise measurements of the tau lepton properties provide stringent tests of
the Standard Model structure and accurate determinations of its parameters. We
overview the present status of a few selected topics: lepton universality, QCD
tests and the determination of alpha_s, m_s and V_us from hadronic tau decays,
and lepton flavor violation phenomena.Comment: Invited talk at the International Workshop on Tau-Charm Physics
(Charm2006), Beijing, China, June 5-7, 2006. 8 pages, 2 figure
Synchonisation of Resonances with Thresholds
The mechanism by which a resonance may be attracted to a sharp threshold is
described with several examples. It involves a threshold cusp interfering
constructively with either or both (i) a resonance produced via confinement,
(ii) attractive t- and u-channel exchanges. More generally, it is suggested
that resonances are eigenstates generated by mixing between confined states and
long-range meson and baryon exchanges.Comment: 8 pages, 4 figures. For Meson08 Proceedings. One important typo
correcte
Extended staggered-flux phases in two-dimensional lattices
Based on the so called - model in two-dimensional (2D) lattices, we
investigate the stabilities of a class of extended staggered-flux (SF) phases
(which are the extensions of the SF phase to
generalized spatial periods) against the Fermi-liquid phase. Surprisingly, when
away from the nesting electron filling, some extended-SF phases take over the
dominant SF phase (the SF phase for the square
lattice, a SF phase for the triangular one), compete with the
Fermi-liquid phase in nontrivial patterns, and still occupy significant space
in the phase diagram through the advantage in the total electronic kinetic
energies. The results can be termed as the generalized Perierls
orbital-antiferromagnetic instabilities of the Fermi-liquid phase in 2D
lattice-electron models.Comment: 5 pages, 5 figure
Nature of the Quantum Phase Transition in Quantum Compass Model
In this work, we show that the quantum compass model on an square lattice can
be mapped to a fermionic model with local density interaction. We introduce a
mean-field approximation where the most important fluctuations, those
perpendicular to the ordering direction, are taken into account exactly. It is
found that the quantum phase transition point at marks a first order
phase transition. We also show that the mean field result is robust against the
remaining fluctuation corrections up to the second order.Comment: 7 pages, 10 fig
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