955 research outputs found
Anderson-type model for a molecule adsorbed on a metal surface
We investigate a modified Anderson model to study the local density of states
(LDOS) of a molecular wire adsorbed on a metal. Using a self-consistent
mean-field type approach we find an exponential decay of the LDOS along the
molecule. A repulsive on-site interaction on the molecule suppresses the
tunneling and decreases the characteristic decay length.Comment: 7 pages (using europhys.sty), 5 EPS figures, To appear in Europhys.
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Spin-Dependent Josephson Current through Double Quantum Dots and Measurement of Entangled Electron States
We study a double quantum dot each dot of which is tunnel-coupled to
superconducting leads. In the Coulomb blockade regime, a spin-dependent
Josephson coupling between two superconductors is induced, as well as an
antiferromagnetic Heisenberg exchange coupling between the spins on the double
dot which can be tuned by the superconducting phase difference. We show that
the correlated spin states-singlet or triplets-on the double dot can be probed
via the Josephson current in a dc-SQUID setup.Comment: 4 pages, 4 figures; To appear in PRB; A few small changes including
reference
Quantum Key Distribution Using Quantum Faraday Rotators
We propose a new quantum key distribution (QKD) protocol based on the fully
quantum mechanical states of the Faraday rotators. The protocol is
unconditionally secure against collective attacks for multi-photon source up to
two photons on a noisy environment. It is also robust against impersonation
attacks. The protocol may be implemented experimentally with the current
spintronics technology on semiconductors.Comment: 7 pages, 7 EPS figure
Anomalous Transmission Phase of a Kondo-Correlated Quantum Dot
We study phase evolution of transmission through a quantum dot with Kondo
correlations. By considering a model that includes nonresonant transmission as
well as the Anderson impurity, we explain unusually large phase evolution of
about in the Kondo valley observed in recent experiments. We argue that
this anomalous phase evolution is a universal property that can be found in the
high-temperature Kondo phase in the presence of the time-reversal symmetry.Comment: 5 pages, 3 figure
Reverse Doppler Effect of Sound
We report observation of reverse Doppler effect in a double negative acoustic
metamaterial. The metamaterial exhibited negative phase velocity and positive
group velocity. The dispersion relation is such that the wavelength
corresponding to higher frequency is longer. We observed that the frequency was
down-shifted for the approaching source, and up-shifted when the source
receded
The prediction of flanking sound transmission below the critical frequency
Although reliable methods exist to predict the apparent sound reduction index of heavy, homogeneous isotopic building constructions, these methods are not appropriate for use with lightweight building constructions which typically have critical frequencies in or above the frequency range of interest. Three main methods have been proposed for extending the prediction of flanking sound transmission to frequencies below the critical frequency
Andreev Bound States in the Kondo Quantum Dots Coupled to Superconducting Leads
We have studied the Kondo quantum dot coupled to two superconducting leads
and investigated the subgap Andreev states using the NRG method. Contrary to
the recent NCA results [Clerk and Ambegaokar, Phys. Rev. B 61, 9109 (2000);
Sellier et al., Phys. Rev. B 72, 174502 (2005)], we observe Andreev states both
below and above the Fermi level.Comment: 5 pages, 5 figure
Josephson current in strongly correlated double quantum dots
We study the transport properties of a serial double quantum dot (DQD)
coupled to two superconducting leads, focusing on the Josephson current through
the DQD and the associated 0- transitions which result from the subtle
interplay between the superconductivity, the Kondo physics, and the inter-dot
superexchange interaction. We examine the competition between the
superconductivity and the Kondo physics by tuning the relative strength
of the superconducting gap and the Kondo temperature
, for different strengths of the superexchange coupling determined by the
interdot tunneling relative to the dot level broadening . We find
strong renormalization of , a significant role of the superexchange coupling
, and a rich phase diagram of the 0 and -junction regimes. In
particular, when both the superconductivity and the exchange interaction are in
close competion with the Kondo physics (), there appears
an island of -phase at large values of the superconducting phase
difference.Comment: 4 pages, 4 figure
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