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 $\sim 50 \mu\phi_{0} / \sqrt{Hz}$ 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