167 research outputs found
A Green-function approach to transport phenomena in quantum pumps
We present a general treatment to study transport phenomena in systems
described by tight-binding Hamiltonians coupled to reservoirs and with one or
more time-periodic potentials. We apply this treatment to the study of
transport phenomena in a double barrier structure with one and two harmonic
potentials. Among other properties, we discuss the origin of the sign of the
net current.Comment: To appear in PR
Symmetry and environment effects on rectification mechanisms in quantum pumps
We consider a paradigmatic model of quantum pumps and discuss its
rectification properties in the framework of a symmetry analysis proposed for
ratchet systems. We discuss the role of the environment in breaking
time-reversal symmetry and the possibility of a finite directed current in the
Hamiltonian limit of annular systems.Comment: To appear as Rapid Communication in PR
Heat production and energy balance in nanoengines driven by time-dependent fields
We present a formalism to study the heat transport and the power developed by
the local driving fields on a quantum system coupled to macroscopic reservoirs.
We show that, quite generally, two important mechanisms can take place: (i)
directed heat transport between reservoirs induced by the ac potentials and
(ii) at slow driving, two oscillating out of phase forces perform work against
each other, while the energy dissipated into the reservoirs is negligibleComment: 5 pages, 4 figure
Rectification of displacement currents in an adiabatic electron pump
Rectification of ac displacement currents generated by periodic variation of
two independent gate voltages of a quantum dot can lead to a dc voltage linear
in the frequency. The presence of this rectified displacement current could
account for the magnetic field symmetry observed in a recent measurement on an
adiabatic quantum electron pump by Switkes et al. [Science 283, 1905 (1999)].Comment: 2 pages, RevTeX; 1 figur
High Bias Transport and Magnetometer Design in Open Quantum Dots
We report transport measurements as a function of bias in open semiconductor
quantum dots. These measurements are well described by an effective electron
temperature derived from Joule heating at the point contacts and cooling by
Wiedemann-Franz out-diffusion of thermal electrons. Using this model, we
propose and analyze a quantum dot based sensor which measures absolute magnetic
field at micron scales with a noise floor of
at 300 mK.Comment: 10 pages including 3 figure
Non-adiabatic effect on Laughlin's argument of the quantum Hall effect
We have numerically studied a non-adiabatic charge transport in the quantum
Hall system pumped by a magnetic flux, as one of the simplest theoretical
realizations of non-adiabatic Thouless pumping. In the adiabatic limit, a
pumped charge is quantized, known as Laughlin's argument in a cylindrical
lattice. In a uniform electric field, we obtained a formula connecting
quantized pumping in the adiabatic limit and no-pumping in the sudden limit.
The intermediate region between the two limits is determined by the Landau gap.
A randomness or impurity effect is also discussed.Comment: 4 pages, 6 figure
Nonequilibrium theory of Coulomb blockade in open quantum dots
We develop a non-equilibrium theory to describe weak Coulomb blockade effects
in open quantum dots. Working within the bosonized description of electrons in
the point contacts, we expose deficiencies in earlier applications of this
method, and address them using a 1/N expansion in the inverse number of
channels. At leading order this yields the self-consistent potential for the
charging interaction. Coulomb blockade effects arise as quantum corrections to
transport at the next order. Our approach unifies the phase functional and
bosonization approaches to the problem, as well as providing a simple picture
for the conductance corrections in terms of renormalization of the dot's
elastic scattering matrix, which is obtained also by elementary perturbation
theory. For the case of ideal contacts, a symmetry argument immediately allows
us to conclude that interactions give no signature in the averaged conductance.
Non-equilibrium applications to the pumped current in a quantum pump are worked
out in detail.Comment: Published versio
Time-reversal symmetry breaking by ac field: Effect of commensurability in the frequency domain
It is shown that the variance of the linear dc conductance fluctuations in an
open quantum dot under a high-frequency ac pumping depends significantly on the
spectral content of the ac field. For a sufficiently strong ac field the dc
conductance fluctuations are much stronger for the periodic pumping than in the
case of the noise ac field of the same intensity. The reduction factor r in a
static magnetic field takes the universal value of 2 only for the white-noise
pumping. In general r may deviate from 2 thus signalling on the time-reversal
symmetry breaking by the ac field. For the bi-harmonic ac field of the form
A(t)=A_{0} [cos(\omega_{1} t)+cos(\omega_{2} t)] we predict the enchancement of
effects of T-symmetry breaking at commensurate frequencies
\omega_{2}/\omega_{1}=P/Q. In the high-temperature limit there is also the
parity effect: the enchancement is only present if either P or Q is even.Comment: 8 pages, 6 figures, submitted for "Electronic Correlations: from
meso- to nano-physics", edited by G. Montambaux and T. Martin, Rencontres de
Morion
Scattering Theory of Dynamic Electrical Transport
We have developed a scattering matrix approach to coherent transport through
an adiabatically driven conductor based on photon-assisted processes. To
describe the energy exchange with the pumping fields we expand the Floquet
scattering matrix up to linear order in driving frequency.Comment: Proceedings QMath9, September 12th-16th, 2004, Giens, Franc
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