166 research outputs found
Electron-phonon coupling in metallic carbon nanotubes: Dispersionless electron propagation despite dissipation
A recent study [Rosati, Dolcini, and Rossi, Appl. Phys. Lett. 106, 243101
(2015)] has predicted that, while in semiconducting single-walled carbon
nanotubes (SWNTs) an electronic wave packet experiences the typical spatial
diffusion of conventional materials, in metallic SWNTs its shape remains
essentially unaltered up to micron distances at room temperature, even in the
presence of the electron-phonon coupling. Here, by utilizing a Lindblad-based
density-matrix approach enabling us to account for both dissipation and
decoherence effects, we test such prediction by analyzing various aspects that
were so far unexplored. In particular, accounting for initial nonequilibrium
excitations, characterized by an excess energy , and including both intra-
and interband phonon scattering, we show that for realistically high values of
the electronic diffusion is extremely small and nearly independent of its
energetic distribution, in spite of a significant energy-dissipation and
decoherence dynamics. Furthermore, we demonstrate that the effect is robust
with respect to the variation of the chemical potential. Our results thus
suggest that metallic SWNTs are a promising platform to realise quantum
channels for the non-dispersive transmission of electronic wave packets.Comment: 14 pages, 7 figure
Fractional charge in the noise of Luttinger liquid systems
The current noise of a voltage biased interacting quantum wire adiabatically
connected to metallic leads is computed in presence of an impurity in the wire.
We find that in the weak backscattering limit the Fano factor characterizing
the ratio between shot noise and backscattering current crucially depends on
the noise frequency relative to the ballistic frequency v_F/gL, where v_F is
the Fermi velocity, g the Luttinger liquid interaction parameter, and L the
length of the wire. In contrast to chiral Luttinger liquids, the noise is not
only due to the Poissonian backscattering of fractionally charged
quasiparticles at the impurity, but also depends on Andreev-type reflections of
plasmons at the contacts, so that the frequency dependence of the noise needs
to be analyzed to extract the fractional charge e*=e g of the bulk excitations.
We show that the frequencies needed to see interaction effects in the Fano
factor are within experimental reach.Comment: 9 pages, 4 figures, conference proceedings of Fluctuations and Noise
2005, Austin, Texa
Appearance of fractional charge in the noise of non-chiral Luttinger liquids
The current noise of a voltage biased interacting quantum wire adiabatically
connected to metallic leads is computed in presence of an impurity in the wire.
We find that in the weak backscattering limit the Fano factor characterizing
the ratio between noise and backscattered current crucially depends on the
noise frequency relative to the ballistic frequency , where
is the Fermi velocity, the Luttinger liquid interaction parameter,
and the length of the wire. In contrast to chiral Luttinger liquids the
noise is not only due to the Poissonian backscattering of fractionally charged
quasiparticles at the impurity, but also depends on Andreev-type reflections at
the contacts, so that the frequency dependence of the noise needs to be
analyzed to extract the fractional charge of the bulk excitations.Comment: 4 pages, 2 figures, final version, to appear in PR
Finite-temperature properties of the Hubbard chain with bond-charge interaction
We investigate the one-dimensional Hubbard model with an additional
bond-charge interaction, recently considered in the description of compounds
that exhibit strong 1D features above the temperature of ordered phases. The
partition function of the model is exactly calculated for a value of the
bond-charge coupling; the behavior of the specific heat and spin susceptibility
as a function of temperature is derived at arbitrary filling, and particularly
discussed across the occurring metal-insulator transition. The results show
that the bond-charge terms weaken the spin excitations of the system.Comment: 5 pages, 3 eps figure
Spin-fermion mappings for even Hamiltonian operators
We revisit the Jordan-Wigner transformation, showing that --rather than a
non-local isomorphism between different fermionic and spin Hamiltonian
operators-- it can be viewed in terms of local identities relating different
realizations of projection operators. The construction works for arbitrary
dimension of the ambient lattice, as well as of the on-site vector space,
generalizing Jordan-Wigner's result. It provides direct mapping of local
quantum spin problems into local fermionic problems (and viceversa), under the
(rather physical) requirement that the latter are described by Hamiltonian's
which are even products of fermionic operators. As an application, we
specialize to mappings between constrained-fermions models and spin 1 models on
chains, obtaining in particular some new integrable spin Hamiltonian, and the
corresponding ground state energies.Comment: 7 pages, ReVTeX file, no figure
Erratum to: Confinement versus interface bound states in spin-orbit coupled nanowires (The European Physical Journal Plus, (2020), 135, 7, (597), 10.1140/epjp/s13360-020-00614-2)
During production mistakes have been introduced
Switching the sign of Josephson current through Aharonov-Bohm interferometry
We investigate the DC Josephson effect in a superconductor-normal
metal-superconductor junction where the normal region consists of a ballistic
ring. We show that a fully controllable -junction can be realized through
the electro-magnetostatic Aharonov-Bohm effect in the ring. The sign and the
magnitude of the supercurrent can be tuned by varying the magnetic flux and the
gate voltage applied to one arm, around suitable values. The implementation in
a realistic set-up is discussed.Comment: 4 pages, 3 figure
Strongly Interacting Luttinger Liquid and Superconductivity in an Exactly Solvable Model
A new family of exactly solvable one dimensional models with a hard-core
repulsive potential is solved by the Bethe Ansatz for an arbitrary hard-core
radius. The exact ground state phase diagrams in a plane 'electron density -
on-site interaction' have been studied for several values of a hard-core
radius. It is shown that superconducting phase and strongly interacting
Luttinger liquid state are coexisted at a high electron density and unusually
high value of repulsive on-site Coulomb interaction.Comment: 4 pages, 2 figures, RevTe
Adiabatic Magnetization of Superconductors as a High-Performance Cooling Mechanism
The adiabatic magnetization of a superconductor is a cooling principle
proposed in the 30s, which has never been exploited up to now. Here we present
a detailed dynamic description of the effect, computing the achievable final
temperatures as well as the process timescales for different superconductors in
various regimes. We show that, although in the experimental conditions explored
so far the method is in fact inefficient, a suitable choice of initial
temperatures and metals can lead to unexpectedly large cooling effect, even in
the presence of dissipative phenomena. Our results suggest that this principle
can be re-envisaged today as a performing refrigeration method to access the
microK regime in nanodevices.Comment: 4 pages, 3 color figure
Wigner-function formalism applied to semiconductor quantum devices: Failure of the conventional boundary condition scheme
The Wigner-function formalism is a well-known approach to model charge transport in semiconductor nanodevices. The primary goal of the present article is to point out and explain the intrinsic limitations of the conventional quantum-device modeling based on such a Wigner-function paradigm, providing a definite answer to open questions related to the application of the conventional spatial boundary condition scheme to the Wigner transport equation. Our analysis shows that (i) in the absence of energy dissipation (coherent limit) the solution of the Wigner equation equipped with given boundary conditions is not unique, and (ii) when dissipation and decoherence phenomena are taken into account via a relaxation-time approximation, the solution, although unique, is not necessarily a physical Wigner function
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