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Search Results: 1 - 10 of 117897 matches for " T. Rejec "
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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.
Quantum entanglement of space domains occupied by interacting electrons
A. Ramsak,J. Mravlje,T. Rejec
Physics , 2008, DOI: 10.1002/pssb.200881570
Abstract: Spin-entanglement of two electrons occupying two spatial regions -- domains -- is expressed in a compact form in terms of spin-spin correlation functions. The power of the formalism is demonstrated on several examples ranging from generation of entanglement by scattering of two electrons to the entanglement of a pair of qubits represented by a double quantum dot coupled to leads. In the latter case the collapse of entanglement due to the Kondo effect is analyzed.
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 of deformable molecules with interaction
J. Mravlje,A. Ramsak,T. Rejec
Physics , 2005, DOI: 10.1103/PhysRevB.72.121403
Abstract: Zero temperature linear response conductance of molecules with Coulomb interaction and with various types of phonon modes is analysed together with local occupation, local moment, charge fluctuations and fluctuations of molecular deformation. Deformation fluctuations are quantitatively related to charge fluctuations which exhibit similarity also to static charge susceptibility.
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.
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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