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Search Results: 1 - 10 of 403322 matches for " J. H. Jefferson "
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Shot noise reduction in quantum wires with "0.7 structure"
A. Ramsak,J. H. Jefferson
Physics , 2005, DOI: 10.1103/PhysRevB.71.161311
Abstract: Shot noise reduction in quantum wires is interpreted within the model for the ''0.7 structure'' in the conductance of near perfect quantum wires [T. Rejec, A. Ramsak, and J.H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. It is shown how the Fano factor structure is related to the specific structure of the conductance as a consequence of the singlet--triplet nature of the resonances with the probability ratio 1:3. An additional feature in the Fano factor, related to the ''0.25 structure'' in conductance, is predicted.
Entanglement and transport anomalies in nanowires
J. H. Jefferson,A. Ramsak,T. Rejec
Physics , 2008, DOI: 10.1088/0953-8984/20/16/164206
Abstract: A shallow potential well in a near-perfect quantum wire will bind a single-electron and behave like a quantum dot, giving rise to spin-dependent resonances of propagating electrons due to Coulomb repulsion and Pauli blocking. It is shown how this may be used to generate full entanglement between static and flying spin-qubits near resonance in a two-electron system via singlet or triplet spin-filtering. In a quantum wire with many electrons, the same pairwise scattering may be used to explain conductance, thermopower and shot-noise anomalies, provided the temperature/energy scale is sufficiently high for Kondo-like many-body effects to be negligible.
Spin-dependent thermoelectric transport coefficients in near-perfect quantum wires
T. Rejec,A. Ramsak,J. H. Jefferson
Physics , 2002, DOI: 10.1103/PhysRevB.65.235301
Abstract: Thermoelectric transport coefficients are determined for semiconductor quantum wires with weak thickness fluctuations. Such systems exhibit anomalies in conductance near 1/4 and 3/4 of 2e^2/h on the rising edge to the first conductance plateau, explained by singlet and triplet resonances of conducting electrons with a single weakly bound electron in the wire [T. Rejec, A. Ramsak, and J.H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. We extend this work to study the Seebeck thermopower coefficient and linear thermal conductance within the framework of the Landauer-Buettiker formalism, which also exhibit anomalous structures. These features are generic and robust, surviving to temperatures of a few degrees. It is shown quantitatively how at elevated temperatures thermal conductance progressively deviates from the Wiedemann-Franz law.
Conductance anomalies and the extended Anderson model for nearly perfect quantum wires
T. Rejec,A. Ramsak,J. H. Jefferson
Physics , 2002, DOI: 10.1103/PhysRevB.67.075311
Abstract: Anomalies near the conductance threshold of nearly perfect semiconductor quantum wires are explained in terms of singlet and triplet resonances of conduction electrons with a single weakly-bound electron in the wire. This is shown to be a universal effect for a wide range of situations in which the effective single-electron confinement is weak. The robustness of this generic behavior is investigated numerically for a wide range of shapes and sizes of cylindrical wires with a bulge. The dependence on gate voltage, source-drain voltage and magnetic field is discussed within the framework of an extended Hubbard model. This model is mapped onto an extended Anderson model, which in the limit of low temperatures is expected to lead to Kondo resonance physics and pronounced many-body effects.
Effect of deconfinement on resonant transport in quantum wires
A. Ramsak,T. Rejec,J. H. Jefferson
Physics , 1998, DOI: 10.1103/PhysRevB.58.4014
Abstract: The effect of deconfinement due to finite band offsets on transport through quantum wires with two constrictions is investigated. It is shown that the increase in resonance linewidth becomes increasingly important as the size is reduced and ultimately places an upper limit on the energy (temperature) scale for which resonances may be observed.
Coulomb Blockade Resonances in Quantum Wires
T. Rejec,A. Ramsak,J. H. Jefferson
Physics , 1999, DOI: 10.1103/PhysRevB.62.12985
Abstract: The conductance through a quantum wire of cylindrical cross section and a weak bulge is solved exactly for two electrons within the Landauer-Buettiker formalism. We show that this 'open' quantum dot exhibits spin-dependent Coulomb blockade resonances resulting in two anomalous structure on the rising edge to the first conductance plateau, one near 0.25(2e^2/h), related to a singlet resonance, and one near 0.7(2e^2/h), related to a triplet resonance. These resonances are generic and robust, occurring for other types of quantum wire and surviving to temperatures of a few degrees.
Entanglement of two delocalised electrons
A. Ramsak,I. Sega,J. H. Jefferson
Physics , 2006, DOI: 10.1103/PhysRevA.74.010304
Abstract: Several convenient formulae for the entanglement of two indistinguishable delocalised spin-1/2 particles are introduced. This generalizes the standard formula for concurrence, valid only in the limit of localised or distinguishable particles. Several illustrative examples are given.
Interacting electrons in a nearly straight quantum wire
T. Rejec,A. Ramsak,J. H. Jefferson
Physics , 2000,
Abstract: The conductance threshold of a clean nearly straight quantum wire in which a single electron is bound is studied. This exhibits spin-dependent conductance anomalies on the rising edge to the first conductance plateau, near G=0.25(2e^{2}/h) and G=0.7(2e^{2}/h), related to a singlet and triplet resonances respectively. We show that the problem may be mapped on to an Anderson-type of Hamiltonian and calculate the energy dependence of the energy parameters in the resulting model.
Anomalies in the conduction edge of quantum wires
T. Rejec,A. Ramsak,J. H. Jefferson
Physics , 2000,
Abstract: We study the conductance threshold of clean nearly straight quantum wires in which an electron is bound. We show that such a system exhibits spin-dependent conductance structures on the rising edge to the first conductance plateau, one near 0.25(2e^2/h), related to a singlet resonance, and one near 0.75(2e^2/h), related to a triplet resonance. As a quantitative example we solve exactly the scattering problem for two-electrons in a wire with circular cross-section and a weak bulge. From the scattering matrix we determine conductance via the Landauer-Buettiker formalism. The conductance anomalies are robust and survive to temperatures of a few degrees. With increasing magnetic field the conductance exhibits a plateau at e^2/h, consistent with recent experiments.
Conductance anomalies in quantum wires
T. Rejec,A. Ramsak,J. H. Jefferson
Physics , 2000, DOI: 10.1088/0953-8984/12/13/101
Abstract: We study the conductance threshold of clean nearly straight quantum wires in the magnetic field. As a quantitative example we solve exactly the scattering problem for two-electrons in a wire with planar geometry and a weak bulge. From the scattering matrix we determine conductance via the Landauer-Buettiker formalism. The conductance anomalies found near 0.25(2e^2/h) and 0.75(2e^2/h) are related to a singlet resonance and a triplet resonance, respectively, and survive to temperatures of a few degrees. With increasing in-plane magnetic field the conductance exhibits a plateau at e^2/h, consistent with recent experiments.
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