9,440 research outputs found
Time-dependent thermoelectric transport for nanoscale thermal machines
We analyze an electronic nanoscale thermal machine driven by time-dependent
environment: besides bias and gate voltage variations, we consider also the
less prevailing time modulation of the couplings between leads and dot. We
provide energy and heat current expressions in such situations, as well as
expressions for the power exchanged between the dot+leads system and its
outside. Calculations are made in the Keldysh nonequilibrium Green's function
framework. We apply these results to design a cyclic refrigerator,
circumventing the ambiguity of defining energy flows between subsystems in the
case of strong coupling. For fast lead-dot coupling modulation, we observe
transient currents which cannot be ascribed to charge tunneling.Comment: 9 pages, 6 figure
Powerful Coulomb-drag thermoelectric engine
We investigate a thermoelectric nano-engine whose properties are steered by
Coulomb interaction. The device whose design decouples charge and energy
currents is made up of two interacting quantum dots connected to three
different reservoirs. We show that, by tailoring the tunnel couplings, this
setup can be made very attractive for energy-harvesting prospects, due to a
delivered power that can be of the order of the quantum bound [R. S. Whitney,
Phys. Rev. Lett. 112, 130601 (2014); Entropy 18, 208 (2016)], with a
concomitant fair efficiency. To unveil its properties beyond the sequential
quantum master equation, we apply a nonequilibrium noncrossing approximation in
the Keldysh Green's function formalism, and a quantum master equation that
includes cotunneling processes. Both approaches are rather qualitatively
similar in a large operating regime where sequential tunneling alone fails.Comment: Published version. (The discussion about the energy current in QME
has been expanded
On strongly coupled quenched QED4, again: chiral symmetry breaking, Goldstone mechanism and the nature of the continuum limit
We explore the possibility of a trivial continuum limit of strongly coupled
quenched QED4 by contrasting our results with a Nambu--Jona Lasinio equation of
state. The data does not compare favorably with such scenario. We study in
detail the interplay of chiral symmetry breaking with the Goldstone mechanism,
and clarify some puzzling features of past results.Comment: Contribution to Lat94, 3 pages, tar-compressed uuencoded ps fil
On the Classification of Automorphic Lie Algebras
It is shown that the problem of reduction can be formulated in a uniform way
using the theory of invariants. This provides a powerful tool of analysis and
it opens the road to new applications of these algebras, beyond the context of
integrable systems. Moreover, it is proven that sl2-Automorphic Lie Algebras
associated to the icosahedral group I, the octahedral group O, the tetrahedral
group T, and the dihedral group Dn are isomorphic. The proof is based on
techniques from classical invariant theory and makes use of Clebsch-Gordan
decomposition and transvectants, Molien functions and the trace-form. This
result provides a complete classification of sl2-Automorphic Lie Algebras
associated to finite groups when the group representations are chosen to be the
same and it is a crucial step towards the complete classification of
Automorphic Lie Algebras.Comment: 29 pages, 1 diagram, 9 tables, standard LaTeX2e, submitted for
publicatio
Hund and pair-hopping signature in transport properties of degenerate nanoscale devices
We investigate the signature of a complete Coulomb interaction in transport
properties of double-orbital nanoscale devices. We analyze the specific effects
of Hund exchange and pair hopping terms, calculating in particular stability
diagrams. It turns out that a crude model, with partial Coulomb interaction,
may lead to a misinterpretation of experiments. In addition, it is shown that
spectral weight transfers induced by gate and bias voltages strongly influence
charge current. The low temperature regime is also investigated, displaying
inelastic cotunneling associated with the exchange term, as well as Kondo
conductance enhancement.Comment: 5 pages, 4 figure
Radiatively Induced Breaking of Conformal Symmetry in a Superpotential
Radiatively induced symmetry breaking is considered for a toy model with one
scalar and one fermion field unified in a superfield. It is shown that the
classical quartic self-interaction of the superfield possesses a quantum
infrared singularity. Application of the Coleman-Weinberg mechanism for
effective potential leads to the appearance of condensates and masses for both
scalar and fermion components. That induces a spontaneous breaking of the
initial classical symmetries: the supersymmetry and the conformal one. The
energy scales for the scalar and fermion condensates appear to be of the same
order, while the renormalization scale is many orders of magnitude higher. A
possibility to relate the considered toy model to conformal symmetry breaking
in the Standard Model is discussed.Comment: Improved final version with new references and misprints corrected, 9
pages , no figure
Higher dimensional Automorphic Lie Algebras
The paper presents the complete classification of Automorphic Lie Algebras
based on , where the symmetry group is finite
and the orbit is any of the exceptional -orbits in .
A key feature of the classification is the study of the algebras in the context
of classical invariant theory. This provides on one hand a powerful tool from
the computational point of view, on the other it opens new questions from an
algebraic perspective, which suggest further applications of these algebras,
beyond the context of integrable systems. In particular, the research shows
that Automorphic Lie Algebras associated to the
groups (tetrahedral, octahedral and
icosahedral groups) depend on the group through the automorphic functions only,
thus they are group independent as Lie algebras. This can be established by
defining a Chevalley normal form for these algebras, generalising this
classical notion to the case of Lie algebras over a polynomial ring.Comment: 43 pages, standard LaTeX2
Conditions for requiring nonlinear thermoelectric transport theory in nanodevices
In this paper, we examine the conditions under which the nonlinear transport
theory is inescapable, when a correlated quantum dot is symmetrically coupled
to two leads submitted to temperature and voltage biases. By detailed numerical
comparisons between nonlinear and linear currents, we show that the claimed
nonlinear behavior in a temperature gradient for the electric current is not so
genuine, and the linear theory made at the operating temperature is unexpectedly robust. This is demonstrated for the single
impurity Anderson model, in different regimes: resonant tunneling, Coulomb
blockade and Kondo regimes
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