Electronic Aharonov-Bohm Effect Induced by Quantum Vibrations

Mechanical displacements of a nanoelectromechanical system (NEMS) shift the electron trajectories and hence perturb phase coherent charge transport through the device. We show theoretically that in the presence of a magnetic feld such quantum-coherent displacements may give rise to an Aharonov-Bohm-type of effect. In particular, we demonstrate that quantum vibrations of a suspended carbon nanotube result in a positive nanotube magnetoresistance, which decreases slowly with the increase of temperature. This effect may enable one to detect quantum displacement fluctuations of a nanomechanical device.Comment: 4 pages, 3 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

Mechanically Induced Thermal Breakdown in Magnetic Shuttle Structures

A theory of a thermally induced single-electron "shuttling" instability in a magnetic nanomechanical device subject to an external magnetic field is presented in the Coulomb blockade regime of electron transport. The model magnetic shuttle device considered comprises a movable metallic grain suspended between two magnetic leads, which are kept at different temperatures and assumed to be fully spin polarized with antiparallel magnetizations. For a given temperature difference shuttling is found to occur for a region of external magnetic fields between a lower and an upper critical field strength, which separate the shuttling regime from normal small-amplitude "vibronic" regimes. We find that (i) the upper critical magnetic field saturates to a constant value in the high temperature limit and that the shuttle instability domain expands with a decrease of the temperature, (ii) the lower critical magnetic field depends not only on the temperature independent phenomenological friction coefficient used in the model but also on intrinsic friction (which vanishes in the high temperature limit) caused by magnetic exchange forces and electron tunneling between the quantum dot and the leads. The feasibility of using thermally driven magnetic shuttle systems to harvest thermal breakdown phenomena is discussed.Comment: 9 pages, 2 figure

Mechanical Cooper pair transportation as a source of long distance superconducting phase coherence

Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote superconductors is shown to establish coherent coupling between them. This coupling is due to entanglement of the movable box with the leads and is manifested in the supression of quantum fluctuations of the relative phase of the order parameters of the leads. It can be probed by attaching a high resistance Josephson junction between the leads and measuring the current through this junction. The current is suppressed with increasing temperature.Comment: 4 pages, 4 figures, RevTeX; Updated version, typos correcte

Quantum Spin Fluctuations as a Source of Long-Range Proximity Effects in Diffusive Ferromagnet-Superconductor Structures

We show that quantum spin fluctuations in inhomogeneous ferromagnets drastically affect the Andreev reflection of electrons and holes at a ferromagnet-superconductor interface. As a result a strong long-range proximity effect appears, associated with electron-hole spin triplet correlations and persisting on a lenght scale typical for non-magnetic materials, but anomalously large for ferromagnets.Comment: 4 pages, 2 figure

Coulomb correlations and coherent charge tunneling in mesoscopic coupled rings

We study the effect of a strong electron-electron (e-e) interaction in a system of two concentric one-dimensional rings with incommensurate areas A_1 and A_2, coupled by a tunnel amplitude. For noninteracting particles the magnetic moment (persistent current) m of the many-body ground state and first excited states is an irregular function of the external magnetic field. In contrast, we show that when strong e-e interactions are present the magnetic field dependence of m becomes periodic. In such a strongly correlated system disorder can only be caused by inter-ring charge fluctuations, controllable by a gate voltage. The oscillation period of m is proportional to 1/(A_1 + A_2) if fluctuations are suppressed. Coherent inter-ring tunneling doubles the period when charge fluctuations are allowed.Comment: 4 pages, 4 eps figure

Influence of Long-Range Coulomb Interactions on the Metal-Insulator Transition in One-Dimensional Strongly Correlated Electron Systems

The influence of long-range Coulomb interactions on the properties of one-dimensional (1D) strongly correlated electron systems in vicinity of the metal-insulator phase transition is considered. It is shown that unscreened repulsive Coulomb forces lead to the formation of a 1D Wigner crystal in the metallic phase and to the transformation of the square-root singularity of the compressibility (characterizing the commensurate-incommensurate transition) to a logarithmic singularity. The properties of the insulating (Mott) phase depend on the character of the short-wavelength screening of the Coulomb forces. For a sufficiently short screening length the characteristics of the charge excitations in the insulating phase are totally determined by the Coulomb interaction and these quasipartic les can be described as quasiclassical Coulomb solitons.Comment: 14 pages, LaTeX, G{\"o}teborg preprint APR 94-3

Diffusion Thermopower at Even Denominator Fractions

We compute the electron diffusion thermopower at compressible Quantum Hall states corresponding to even denominator fractions in the framework of the composite fermion approach. It is shown that the deviation from the linear low temperature behavior of the termopower is dominated by the logarithmic temperature corrections to the conductivity and not to the thermoelectric coefficient, although such terms are present in both quantities. The enhanced magnitude of this effect compared to the zero field case may allow its observation with the existing experimental techniques.Comment: Latex, 12 pages, Nordita repor

Optimizing thermal transport in the Falicov-Kimball model: binary-alloy picture

We analyze the thermal transport properties of the Falicov-Kimball model concentrating on locating regions of parameter space where the thermoelectric figure-of-merit ZT is large. We focus on high temperature for power generation applications and low temperature for cooling applications. We constrain the static particles (ions) to have a fixed concentration, and vary the conduction electron concentration as in the binary-alloy picture of the Falicov-Kimball model. We find a large region of parameter space with ZT>1 at high temperature and we find a small region of parameter space with ZT>1 at low temperature for correlated systems, but we believe inclusion of the lattice thermal conductivity will greatly reduce the low-temperature figure-of-merit.Comment: 13 pages, 14 figures, typeset with ReVTe

Spectroscopy of the Potential Profile in a Ballistic Quantum Constriction

We present a theory for the nonlinear current-voltage characteristics of a ballistic quantum constriction. Nonlinear features first develop because of above-barrier reflection from the potential profile, created by impurities in the vicinity of the constriction. The nonlinearity appears on a small voltage scale and makes it possible to determine distances between impurities as well as the magnitude of the impurity potentials.Comment: 3 pages, 4 figures (availiable upon request), REVTEX, Applied Physics Report 93-5