Archivio della ricerca dell'Università di Modena e Reggio Emiliahttps://iris.unimore.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Fri, 06 Dec 2019 05:18:28 GMT2019-12-06T05:18:28Z10171Pairing of a few Fermi atoms in one dimensionhttp://hdl.handle.net/11380/1077506Titolo: Pairing of a few Fermi atoms in one dimension
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11380/10775062015-01-01T00:00:00ZQuantum phases of correlated electrons in artificial molecules under magnetic fieldshttp://hdl.handle.net/11380/421418Titolo: Quantum phases of correlated electrons in artificial molecules under magnetic fields
Abstract: We investigate the stability of few-electron quantum phases in vertically coupled quantum dots under a magnetic field of arbitrary strength and direction. The orbital and spin stability diagrams of realistic devices containing up to five electrons, from strong to weak interdot coupling, is determined. Correlation effects and realistic sample geometries are fully taken into account within the full configuration interaction method. In general, the magnetic field drives the system into a strongly correlated regime by modulating the single-particle gaps. In coupled quantum dots different components of the field, either parallel or perpendicular to the tunneling direction, affect single-dot orbitals and tunneling energy, respectively. Therefore the stability of the quantum phases is related to different correlation mechanisms, depending on the field direction. Comparison of exact diagonalization results with simple models allows one to identify the specific role of correlations.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/11380/4214182006-01-01T00:00:00ZImaging correlated wave functions of few-electron quantum dots: theory and STS experimentshttp://hdl.handle.net/11380/421414Titolo: Imaging correlated wave functions of few-electron quantum dots: theory and STS experiments
Abstract: We show both theoretically and experimentally that scanning tunneling spectroscopy (STS) images of semiconductor quantum dots may display clear signatures of electron-electron correlation. We apply many-body tunneling theory to a realistic model, which fully takes into account correlation effects and dot anisotropy. Comparing measured STS images of freestanding InAs quantum dots with those calculated by the full configuration interaction method, we explain the wave-function sequence in terms of images of one- and two-electron states. The STS map corresponding to double charging is significantly distorted by electron correlation with respect to the noninteracting case.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/11380/4214142007-01-01T00:00:00ZCorrelation Effects in Wave Function Mapping of Molecular Beam Epitaxy Grown Quantum Dotshttp://hdl.handle.net/11380/737862Titolo: Correlation Effects in Wave Function Mapping of Molecular Beam Epitaxy Grown Quantum Dots
Abstract: We investigate correlation effects in the regime of a few electrons in uncapped InAs quantum dots by tunneling spectroscopy and wave function (WF) mapping at high tunneling currents where electron-electron interactions become relevant. Four clearly resolved states are found, whose approximate symmetries are roughly s and p, in order of increasing energy. Because the major axes of the p-like states coincide, the WF sequence is inconsistent with the imaging of independent-electron orbitals. The results are explained in terms of many-body tunneling theory, by comparing measured maps with those calculated by taking correlation effects into account.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/11380/7378622007-01-01T00:00:00ZRaman Signatures of Classical and Quantum Phases in Coupled Dots: a Theoretical Predictionhttp://hdl.handle.net/11380/455007Titolo: Raman Signatures of Classical and Quantum Phases in Coupled Dots: a Theoretical Prediction
Abstract: We study electron molecules in realistic vertically coupled quantum dots in a strong magnetic field. Computing the energy spectrum, pair correlation functions, and dynamical form factor as a function of inter-dot coupling via diagonalization of the many-body Hamiltonian, we identify structural transitions between different phases, some of which do not have a classical counterpart. The calculated Raman cross-section shows how such phases can be experimentally singled out.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/11380/4550072002-01-01T00:00:00ZImaging quasi-particle wavefunctions in quantum dots in via tunneling spectroscopyhttp://hdl.handle.net/11380/455016Titolo: Imaging quasi-particle wavefunctions in quantum dots in via tunneling spectroscopy
Abstract: We show that in quantum dots the physical quantities probed by local tunneling spectroscopies-namely, the quasiparticle wave functions of interacting electrons-can considerably deviate from their single-particle counterparts as an effect of Coulomb correlation. From the exact solution of the few-particle Hamiltonian for prototype dots, we find that such deviations are crucial to predict wave function images at low electron densities or high magnetic fields.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11380/4550162005-01-01T00:00:00ZField-controlled suppression of phonon-induced transitions in coupled quantum dotshttp://hdl.handle.net/11380/454995Titolo: Field-controlled suppression of phonon-induced transitions in coupled quantum dots
Abstract: We suggest that order-of-magnitude reduction of the longitudinal-acoustic phonon scattering rate, the dominant decoherence mechanism in quantum dots, can be achieved in coupled structures by the application of an external electric or magnetic field. Modulation of the scattering rate is traced to the relation between the wavelength of the emitted phonon and the length scale of delocalized electron wave functions. Explicit calculations for realistic devices, performed with a Fermi golden rule approach and a fully three-dimensional description of the electronic quantum states, show that the lifetime of specific states can achieve tens of microseconds. Our findings extend the feasibility basis of many proposals for quantum gates based on coupled quantum dots. (C) 2004 American Institute of Physics.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11380/4549952004-01-01T00:00:00ZSpin excitations in few-electrons AlGaAs/GaAs quantum dots probed by inelastic light scatteringhttp://hdl.handle.net/11380/421419Titolo: Spin excitations in few-electrons AlGaAs/GaAs quantum dots probed by inelastic light scattering
Abstract: We present recent studies of electronic excitations in nanofabricated AlGaAs/GaAs semiconductor quantum dots (QDs) by resonant inelastic light scattering. The resonant light scattering spectra are dominated by excitations from parity-allowed inter-shell transitions between Fock-Darwin levels. In QDs With very few electrons the resonant spectra are characterized by distinct charge and spin excitations that reveal the strong impact of both exchange and correlation effects. A sharp inter-shell spin excitation of the triplet spin QD state with four electrons is identified. (c) 2006 Elsevier B.V. All rights reserved.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/11380/4214192006-01-01T00:00:00ZCorrelated states and spin transitions in nanofabricated AlGaAs/GaAs few-electron quantum dots probed by inelastic light scatteringhttp://hdl.handle.net/11380/612029Titolo: Correlated states and spin transitions in nanofabricated AlGaAs/GaAs few-electron quantum dots probed by inelastic light scattering
Abstract: Spin transitions and correlated few-electron states are investigated by resonant inelastic light scattering in dilute arrays of GaAs/AlGaAs modulation-doped quantum dots (QDs) fabricated by electron-beam lithography and low impact reactive-ion etching. We focus on QDs with four electrons. We show that at moderate magnetic fields, the ground state is a singlet with total spin S = 0. A rich spectrum of distinct spin and charge inter-shell excitations is found, which cannot be described by a mean-field Hartree-Fock framework based on the quantum description of Fock-Darwin energy levels. Instead, the experimental results are well modeled by numerical evaluations within a full configuration interaction approach that highlights the impact of correlation effects in this configuration. This work demonstrates that the sensitivity reached by resonant inelastic light scattering enables the study of few-electron effects in QDs formed by state-of-the-art nanofabrication processes under the extreme conditions of low temperatures and high magnetic fields. (C) 2007 Elsevier B.V. All rights reserved.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/11380/6120292008-01-01T00:00:00ZEffect of the Coulomb interaction on the electron relaxation of weakly-confined quantum dot systems using the full configuration interaction approachhttp://hdl.handle.net/11380/421417Titolo: Effect of the Coulomb interaction on the electron relaxation of weakly-confined quantum dot systems using the full configuration interaction approach
Abstract: We study acoustic-phonon-induced relaxation of charge excitations in single and tunnel-coupled quantum dots containing few confined interacting electrons. The full configuration interaction approach is used to account for the electron-electron repulsion. Electron-phonon interaction is accounted for through both deformation potential and piezoelectric field mechanisms. We show that electronic correlations generally reduce intradot and interdot transition rates with respect to corresponding single-electron transitions, but this effect is lessened by external magnetic fields. On the other hand, piezoelectric field scattering is found to become the dominant relaxation mechanism as the number of confined electrons increases. Previous proposals to strongly suppress electron-phonon coupling in properly designed single-electron quantum dots are shown to hold also in multielectron devices. Our results indicate that few-electron orbital degrees of freedom are more stable than single-electron ones
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/11380/4214172006-01-01T00:00:00Z