604 research outputs found
Bistability of persistent currents in mesoscopic rings
We study the persistent currents flowing in a mesoscopic ring threaded by a
magnetic flux and connected to a stub of finite length. Multistability
processes and Coulomb blockade are demonstrated to be present in this system.
These properties are functions of the magnetic flux crossing the ring which
plays the role that the external applied potential fulfills in the
multistability behaviour of the standard mesoscopic heterostructures.Comment: 13 pages (Revtex), 4 PostScript figures. Send e-mail to:
[email protected]
Persistence of Dromiciops gliroides in landscapes dominated by Pinus radiata plantations
© The Author(s). 2017. Background: Monitos del monte (Dromiciops gliroides) are old-growth forest specialists and, thus, believed to be very sensitive to habitat transformation, although some recent studies show some level of plasticity of their habitat selection patterns. Findings: In this note we report on records of D. gliroides living in a very modified environment, composed mostly by industrial pine plantations and small fragments of Nothofagus spp. forests and we report the extension of the northernmost limit of its currently known distribution. Conclusions: Although highly reliant on native vegetation, Dromiciops gliroides has been able to persist in industrial forest landscapes dominated by pine plantations
Transport through quantum dots: A combined DMRG and cluster-embedding study
The numerical analysis of strongly interacting nanostructures requires
powerful techniques. Recently developed methods, such as the time-dependent
density matrix renormalization group (tDMRG) approach or the embedded-cluster
approximation (ECA), rely on the numerical solution of clusters of finite size.
For the interpretation of numerical results, it is therefore crucial to
understand finite-size effects in detail. In this work, we present a careful
finite-size analysis for the examples of one quantum dot, as well as three
serially connected quantum dots. Depending on odd-even effects, physically
quite different results may emerge from clusters that do not differ much in
their size. We provide a solution to a recent controversy over results obtained
with ECA for three quantum dots. In particular, using the optimum clusters
discussed in this paper, the parameter range in which ECA can reliably be
applied is increased, as we show for the case of three quantum dots. As a
practical procedure, we propose that a comparison of results for static
quantities against those of quasi-exact methods, such as the ground-state
density matrix renormalization group (DMRG) method or exact diagonalization,
serves to identify the optimum cluster type. In the examples studied here, we
find that to observe signatures of the Kondo effect in finite systems, the best
clusters involving dots and leads must have a total z-component of the spin
equal to zero.Comment: 16 pages, 14 figures, revised version to appear in Eur. Phys. J. B,
additional reference
Fractional Aharonov-Bohm effect in mesoscopic rings
We study the effects of correlations on a one dimensional ring threaded by a
uniform magnetic flux. In order to describe the interaction between particles,
we work in the framework of the U Hubbard and - models. We focus
on the dilute limit. Our results suggest the posibility that the persistent
current has an anomalous periodicity , where is an integer in
the range ( is the number of particles in the ring
and is the flux quantum). We found that this result depends neither
on disorder nor on the detailed form of the interaction, while remains the on
site infinite repulsion.Comment: 14 pages (Revtex), 5 postscript figures. Send e-mail to:
[email protected]
Pyrazolium- versus imidazolium-based ionic liquids: Structure, dynamics and physicochemical properties
Ionic liquids (ILs) composed of two different pyrazolium cations with dicyanamide and bis(trifluoromethanesulfonyl)imide anions have been synthesized and characterized by NMR, Kamlet-Taft solvatochromic parameters, conductivity and rheological measurements, as well as ab initio calculations. Density functional calculations for the two pyrazolium cations, 1-butyl-2- methylpyrazolium [bmpz] and 1-butyl-2,3,5-trimethylpyrazolium [bm 3pz], provide a full picture of their conformational states. Homo- and heteronuclear NOE show aggregation motives sensitive to steric hindrance and the anions' nature. Self-diffusion coefficients D for the anion and the cation have been measured by pulsed field gradient spin-echo NMR (PGSE-NMR). The ionic diffusivity is influenced by their chemical structure and steric hindrance, giving the order Dcation > Danion for all of the examined compounds. The measured ion diffusion coefficients, viscosities, and ionic conductivity follow the Vogel-Fulcher-Tammann (VFT) equation for the temperature dependencies, and the best-fit parameters have been determined. Solvatochromic parameters indicate an increased ion association upon going from bis(trifluoromethanesulfonyl)imide to dicyanamide-based pyrazolium salts, as well as specific hydrogen bond donor capability of H atoms on the pyrazolium ring. All of these physical properties are compared to those of an analogous series of imidazolium-based ILs
A Novel Approach to Study Highly Correlated Nanostructures: The Logarithmic Discretization Embedded Cluster Approximation
This work proposes a new approach to study transport properties of highly
correlated local structures. The method, dubbed the Logarithmic Discretization
Embedded Cluster Approximation (LDECA), consists of diagonalizing a finite
cluster containing the many-body terms of the Hamiltonian and embedding it into
the rest of the system, combined with Wilson's idea of a logarithmic
discretization of the representation of the Hamiltonian. The physics associated
with both one embedded dot and a double-dot side-coupled to leads is discussed
in detail. In the former case, the results perfectly agree with Bethe ansatz
data, while in the latter, the physics obtained is framed in the conceptual
background of a two-stage Kondo problem. A many-body formalism provides a solid
theoretical foundation to the method. We argue that LDECA is well suited to
study complicated problems such as transport through molecules or quantum dot
structures with complex ground states.Comment: 17 pages, 13 figure
Persistent currents in diffusive metallic cavities: Large values and anomalous scaling with disorder
The effect of disorder on confined metallic cavities with an Aharonov-Bohm
flux line is addressed. We find that, even deep in the diffusive regime, large
values of persistent currents may arise for a wide variety of geometries. We
present numerical results supporting an anomalous scaling law of the average
typical current with the strength of disorder , with . This is contrasted with previously
reported results obtained for cylindrical samples where a scaling has been found. Possible links to, up to date, unexplained
experimental data are finally discussed.Comment: 5 pages, 4 figure
Asymmetric transmission and anomalous refraction in metal nanowires metasurface
Here we investigated the asymmetric transmission and the anomalous refraction introduced by a metasurface of bent gold nanowires. The refraction follows the generalized Snell's law that takes into account the resonant behavior of metallic nanostructures located at the interface between two dielectrics. Measurements performed in the linear optical regime reveal a large sensitivity to the subwavelength features of the gold nanostructures
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