Velocity shift of surface acoustic waves due to interaction with composite fermions in a modulated structure

We study the effect of a periodic density modulation on surface acoustic wave (SAW) propagation along a 2D electron gas near Landau level filling $\nu=1/2$. Within the composite fermion theory, the problem is described in terms of fermions subject to a spatially modulated magnetic field and scattered by a random magnetic field. We find that a few percent modulation induces a large peak in the SAW velocity shift, as has been observed recently by Willett et al. As further support of this theory we find the dc resistivity to be in good agreement with recent data of Smet et al.Comment: revised version resubmitted to PRL. Part concerning dc transport corrected and extended. A new figure showing dc resistivity in comparison with experiment of Smet et al include

Kondo effect in complex mesoscopic structures

We study the Kondo effect of a quantum dot placed in a complex mesoscopic structure. Assuming that electronic interactions are taking place solely on the dot, and focusing on the infinite Hubbard interaction limit, we use a decoupling scheme to obtain an explicit analytic approximate expression for the dot Green function, which fulfills certain Fermi-liquid relations at zero temperature. The details of the complex structure enter into this expression only via the self-energy for the non-interacting case. The effectiveness of the expression is demonstrated for the single impurity Anderson model and for the T-shaped network.Comment: 12 pages 6 figure

Magnetic field symmetry of pump currents of adiabatically driven mesoscopic structures

We examine the scattering properties of a slowly and periodically driven mesoscopic sample using the Floquet function approach. One might expect that at sufficiently low driving frequencies it is only the frozen scattering matrix which is important. The frozen scattering matrix reflects the properties of the sample at a given instant of time. Indeed many aspects of adiabatic scattering can be described in terms of the frozen scattering matrix. However, we demonstrate that the Floquet scattering matrix, to first order in the driving frequency, is determined by an additional matrix which reflects the fact that the scatterer is time-dependent. This low frequency irreducible part of the Floquet matrix has symmetry properties with respect to time and/or a magnetic field direction reversal opposite to that of the frozen scattering matrix. We investigate the quantum rectification properties of a pump which additionally is subject to an external dc voltage. We split the dc current flowing through the pump into several parts with well defined properties with respect to a magnetic field and/or an applied voltage inversion.Comment: 13 pages, 4 figure

DC spin generation by junctions with AC driven spin-orbit interaction

An unbiased one-dimensional weak link between two terminals, subjected to the Rashba spin-orbit interaction caused by an AC electric field which rotates periodically in the plane perpendicular to the link, is shown to inject spin-polarized electrons into the terminals. The injected spin-polarization has a DC component along the link and a rotating transverse component in the perpendicular plane. In the adiabatic, low rotation-frequency regime, these polarization components are proportional to the frequency. The DC component of the polarization vanishes for a linearly-polarized electric field.Comment: published versio

Quantized adiabatic quantum pumping due to interference

Recent theoretical calculations, demonstrating that quantized charge transfer due to adiabatically modulated potentials in mesoscopic devices can result purely from the interference of the electron wave functions (without invoking electron-electron interactions) are reviewed: (1) A new formula is derived for the pumped charge Q (per period); It reproduces the Brouwer formula without a bias, and also yields the effect of the modulating potential on the Landauer formula in the presence of a bias. (2) For a turnstile geometry, with time-dependent gate voltages V_L(t) and V_R(t), the magnitude and sign of Q are determined by the relative position and orientation of the closed contour traversed by the system in the {V_L-V_R} plane, relative to the transmission resonances in that plane. Integer values of Q (in units of e) are achieved when a transmission peak falls inside the contour, and are given by the winding number of the contour. (3) When the modulating potential is due to surface acoustic waves, Q exhibits a staircase structure, with integer values, reminiscent of experimental observations.Comment: Invited talk, Localization, Tokyo, August 200

Measuring the Kondo effect in the Aharonov-Bohm interferometer

The conductance ${\cal G}$ of an Aharonov-Bohm interferometer (ABI), with a strongly correlated quantum dot on one arm, is expressed in terms of the dot Green function, $G_{dd}$, the magnetic flux $\phi$ and the non-interacting parameters of the ABI. We show that one can extract $G_{dd}$ from the observed oscillations of ${\cal G}$ with $\phi$, for both closed and open ABI's. In the latter case, the phase shift $\beta$ deduced from ${\cal G} \approx A+B\cos(\phi+\beta)$ depends strongly on the ABI's parameters, and usually $\beta \ne \pi/2$. These parameters may also reduce the Kondo temperature, eliminating the Kondo behavior

Three-terminal thermoelectric transport through a molecule placed on an Aharonov-Bohm ring

The thermoelectric transport through a ring threaded by an Aharonov-Bohm flux, with a molecular bridge on one of its arms, is analyzed. The transport electrons also interact with the vibrational excitations of that molecule. This nano-system is connected to three terminals: two are electronic reservoirs, which supply the transport electrons, and the third is the phonon bath which thermalizes the molecular vibrations. Expressions for the transport coefficients, relating all charge and heat currents to the temperature and chemical potential differences between the terminals, are derived to second order in the electron-vibration coupling. At linear response, all these coefficients obey the full Onsager-Casimir relations. When the phonon bath is held at a temperature different from those of the electronic reservoirs, a heat current exchanged between the molecular vibrations and the transport electrons can be converted into electric and/or heat electronic currents. The related transport coefficients, which exist only due to the electron-vibration coupling, change sign under the interchange between the electronic terminals and the sign change of the magnetic flux. It is also demonstrated that the Aharonov-Bohm flux can enhance this type of conversion.Comment: Added clearer kists of the new result

Phonon Spectroscopy by Electric Measurements of Coupled Quantum Dots

We propose phonon spectroscopy by electric measurements of the low-temperature conductance of coupled-quantum dots, specifically employing dephasing of the quantum electronic transport by the phonons. The setup we consider consists of a T-shaped double-quantum-dot (DQD) system in which only one of the dots (dot 1) is connected to external leads and the other (dot 2) is coupled solely to the first one. For noninteracting electrons, the differential conductance of such a system vanishes at a voltage located in-between the energies of the bonding and the anti-bonding states, due to destructive interference. When electron-phonon (e-ph) on the DQD is invoked, we find that, at low temperatures, phonon emission taking place on dot 1 does not affect the interference, while phonon emission from dot 2 suppresses it. The amount of this suppression, as a function of the bias voltage, follows the effective e-ph coupling reflecting the phonon density of states and can be used for phonon spectroscopy.Comment: 9 pages, 6 figure