240 research outputs found
Fano versus Kondo Resonances in a Multilevel "Semi-Open" Quantum Dot
Linear conductance across a large quantum dot via a single level e_0 with
large hybridization to the contacts is strongly sensitive to quasi-bound states
localized in the dot and weakly coupled to e_0. It oscillates with the gate
voltage due to interference of the Fano type. At low temperature and Coulomb
blockade, Kondo correlations damp the oscillations on an extended range of gate
voltage values, by freezing the occupancy of the e_0 level itself. As a
consequence, antiresonances of Fano origin are washed out. The results are in
good correspondence with experimental data for a large quantum dot in the
semi-open regime.Comment: 4 eps figures, RevTex format, revised version, to appear in Phys.
Rev. Letter
Quantum interference of electrons in a ring: tuning of the geometrical phase
We calculate the oscillations of the DC conductance across a mesoscopic ring,
simultaneously tuned by applied magnetic and electric fields orthogonal to the
ring. The oscillations depend on the Aharonov-Bohm flux and of the spin-orbit
coupling. They result from mixing of the dynamical phase, including the Zeeman
spin splitting, and of geometric phases. By changing the applied fields, the
geometric phase contribution to the conductance oscillations can be tuned from
the adiabatic (Berry) to the nonadiabatic (Ahronov-Anandan) regime. To model a
realistic device, we also include nonzero backscattering at the connection
between ring and contacts, and a random phase for electron wavefunction,
accounting for dephasing due to disorder.Comment: 4 pages, 3 figures, minor change
Spin Hall effect in a two-dimensional electron gas in the presence of a magnetic field
We study the spin Hall effect of a two-dimensional electron gas in the
presence of a magnetic field and both the Rashba and Dresselhaus spin-orbit
interactions. We show that the value of the spin Hall conductivity, which is
finite only if the Zeeman spin splitting is taken into account, may be tuned by
varying the ratio of the in-plane and out-of-plane components of the applied
magnetic field. We identify the origin of this behavior with the different role
played by the interplay of spin-orbit and Zeeman couplings for in-plane and
out-of-plane magnetic field components.Comment: 5 pages, 5 figures, submitte
Boundary quantum critical phenomena with entanglement renormalization
We extend the formalism of entanglement renormalization to the study of
boundary critical phenomena. The multi-scale entanglement renormalization
ansatz (MERA), in its scale invariant version, offers a very compact
approximation to quantum critical ground states. Here we show that, by adding a
boundary to the scale invariant MERA, an accurate approximation to the critical
ground state of an infinite chain with a boundary is obtained, from which one
can extract boundary scaling operators and their scaling dimensions. Our
construction, valid for arbitrary critical systems, produces an effective chain
with explicit separation of energy scales that relates to Wilson's RG
formulation of the Kondo problem. We test the approach by studying the quantum
critical Ising model with free and fixed boundary conditions.Comment: 8 pages, 12 figures, for a related work see arXiv:0912.289
Charge dynamics effects in conductance through a large semi-open quantum dot
Fano lineshapes in resonant transmission in a quantum dot imply interference
between localized and extended states. The influence of the charge accumulated
at the localized levels, which screens the external gate voltage acting on the
conduction channel is investigated. The modified Fano q parameter and the
resonant conduction is derived starting from a microscopic Hamiltonian. The
latest experiments on "charge sensing" and ``Coulomb modified Fano sensing ``
compare well with the results of the present model.Comment: 5 pages, 4 figures, RevTex styl
Influence of Topological Edge States on the Properties of Al/Bi2Se3/Al Hybrid Josephson Devices
In superconductor-topological insulator-superconductor hybrid junctions, the
barrier edge states are expected to be protected against backscattering, to
generate unconventional proximity effects, and, possibly, to signal the
presence of Majorana fermions. The standards of proximity modes for these types
of structures have to be settled for a neat identification of possible new
entities. Through a systematic and complete set of measurements of the
Josephson properties we find evidence of ballistic transport in coplanar
Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the
topological edge state. The shunting effect of the bulk only influences the
normal transport. This behavior, which can be considered to some extent
universal, is fairly independent of the specific features of superconducting
electrodes. A comparative study of Shubnikov - de Haas oscillations and
Scanning Tunneling Spectroscopy gave an experimental signature compatible with
a two dimensional electron transport channel with a Dirac dispersion relation.
A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable
step to drive Josephson junctions in the proper regime to detect possible
distinctive features of Majorana fermions.Comment: 11 pages, 14 figure
Hyperbolic Deformation on Quantum Lattice Hamiltonians
A group of non-uniform quantum lattice Hamiltonians in one dimension is
introduced, which is related to the hyperbolic -dimensional space. The
Hamiltonians contain only nearest neighbor interactions whose strength is
proportional to , where is the lattice index and where
is a deformation parameter. In the limit the
Hamiltonians become uniform. Spacial translation of the deformed Hamiltonians
is induced by the corner Hamiltonians. As a simple example, we investigate the
ground state of the deformed Heisenberg spin chain by use of the
density matrix renormalization group (DMRG) method. It is shown that the ground
state is dimerized when is finite. Spin correlation function show
exponential decay, and the boundary effect decreases with increasing .Comment: 5 pages, 4 figure
Information-seeking behavior of catalog users
This study is based on the data from a survey of catalog use at three university libraries and one public library. Both "known-item" searches and "subject" searches were analyzed. The characteristics of the user population were examined and methodological problems of the survey were discussed. A relation was found between the academic rank of the catalog users and type of search that they carry out. Some of the factors influencing the success or failure of the search were analyzed, and the meaning of "success" for the two types of search was discussed. The study investigated trends in search strategies as well as degree of perseverance of catalog searchers. Implications for the design of modern information retrieval systems were pointed out.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32647/1/0000010.pd
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