arXiv subjects

Elisa Molinari

Publications and source records attributed to Elisa Molinari.

At least 73 records · Page 4Linked to original sources

arXiv2004

Optical near-field mapping of excitons and biexcitons in naturally occurring semiconductor quantum dots

We calculate the near-field optical spectra of excitons and biexcitons in semiconductor quantum dots naturally occurring at interface fluctuations in GaAs-based quantum wells, using a non-local description of the response function to a spatially modulated electro-magnetic field. The relative intensity of the lowest, far-field forbidden excitonic states is predicted; the spatial extension of the ground biexciton state is found in agreement with recently published experiments.

cond-mat.mes-hall↗

arXiv2004

Electronic properties of guanine-based nanowires

We present a first-principle study of the electronic and conduction properties of a few classes of nanowires constituted of guanine (G) molecules, self-assembled in different geometries. We first analyze the effect of the vertical $π$-$π$ interaction in model G-stack columns. Then, we exploit the results obtained from those models to interpret the features of realistic stacked and hydrogen-bonded structures, namely the guanine quadruple helices and the planar ribbons. With respect to natural DNA, the different structures as well as the inclusion of metal cations, drastically affect the bonding pattern among the bases, introducing novel features in the electronic properties of the systems. These supramolecular G-aggregates, alternative to DNA, are expected to show intersting properties for molecular elec tronics applications.

cond-mat.soft↗

arXiv2004

Electron channels in biomolecular nanowires

We report a first-principle study of the electronic and conduction properties of a quadruple-helix guanine wire (G4-wire), a DNA-derivative, with inner potassium ions. The analysis of the electronic structure highlights the presence of energy manifolds that are equivalent to the bands of (semi)conducting materials, and reveals the formation of extended electron channels available for charge transport along the wire. The specific metal-nucleobase interactions affect the electronic properties at the Fermi level, leading the wire to behave as an intrinsically p-doped system.

cond-mat.soft↗

arXiv2002

Few-electron liquid and solid phases in artificial molecules at high magnetic field

Coupled semiconductor quantum dots form artificial molecules where relevant energy scales controlling the interacting ground state can be easily tuned. By applying an external magnetic field it is possible to drive the system from a weak to a strong correlation regime where eventually electrons localize in space in an ordered manner reminiscent of the two-dimensional Wigner crystal. We explore the phase diagram of such "Wigner molecules" analyzing the angular correlation function obtained by the Configuration Interaction solution of the full interacting Hamiltonian. Focus is on the role of tunneling in stabilizing different ground states.

cond-mat.mes-hall↗

arXiv2002

Solid state molecular rectifier based on self organized metalloproteins

Recently, great attention has been paid to the possibility of implementing hybrid electronic devices exploiting the self-assembling properties of single molecules. Impressive progress has been done in this field by using organic molecules and macromolecules. However, the use of biomolecules is of great interest because of their larger size (few nanometers) and of their intrinsic functional properties. Here, we show that electron-transfer proteins, such as the blue copper protein azurin (Az), can be used to fabricate biomolecular electronic devices exploiting their intrinsic redox properties, self assembly capability and surface charge distribution. The device implementation follows a bottom-up approach in which the self assembled protein layer interconnects nanoscale electrodes fabricated by electron beam lithography, and leads to efficient rectifying behavior at room temperature.

cond-mat.mtrl-sci↗

arXiv2002

Optically induced coherence effects in `artificial atoms and molecules'

Using a master-equation approach for the description of coherent and incoherent dynamics in `artificial atoms and molecules', we present a theoretical analysis of situations where intense laser fields lead to pronounced renormalizations of carrier states. Such enhanced light-matter interactions allow for the solid-state implementation of effects hitherto only observable in atomic systems. Two prototypical examples will be presented: first, we show how two intense laser pulses can be exploited for a robust and high-fidelity population transfer of carrier states in coupled quantum dots; second, we discuss the possibility of observing self-induced transparency in a sample of inhomogenously broadened quantum dots, a phenomenon where intense laser pulses propagate without suffering significant losses.

cond-mat.mes-hall↗

arXiv2002

Solid state effects on exciton states and optical properties of PPV

We perform ab initio calculations of optical properties for a typical semiconductor conjugated polymer, poly-para-phenylenevinylene, in both isolated chain and crystalline packing. In order to obtain results for excitonic energies and real-space wavefunctions we explicitly include electron-hole interaction within the density-matrix formalism. We find that the details of crystalline arrangement crucially affect the optical properties, leading to a richer exciton structure and opening non-radiative decay channels. This has implications for the optical activity and optoelectronic applications of polymer films.

cond-mat.mtrl-sci↗

arXiv2002

Electron-hole localization in coupled quantum dots

We theoretically investigate correlated electron-hole states in vertically coupled quantum dots. Employing a prototypical double-dot confinement and a configuration-interaction description for the electron-hole states, it is shown that the few-particle ground state undergoes transitions between different quantum states as a function of the interdot distance, resulting in unexpected spatial correlations among carriers and in electron-hole localization. Such transitions provide a direct manifestations of inter- and intradot correlations, which can be directly monitored in experiments.

cond-mat.mes-hall↗

arXiv2002

Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction

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.

cond-mat.mes-hall↗

arXiv2001

Quantum phases in artificial molecules

The many-body state of carriers confined in a quantum dot is controlled by the balance between their kinetic energy and their Coulomb correlation. In coupled quantum dots, both can be tuned by varying the inter-dot tunneling and interactions. Using a theoretical approach based on the diagonalization of the exact Hamiltonian, we show that transitions between different quantum phases can be induced through inter-dot coupling both for a system of few electrons (or holes) and for aggregates of electrons and holes. We discuss their manifestations in addition energy spectra (accessible through capacitance or transport experiments) and optical spectra.

cond-mat.mes-hall↗

arXiv2001

Quantum-information processing in semiconductor quantum dots

We propose an all-optical implementation of quantum-information processing in semiconductor quantum dots, where electron-hole excitations (excitons) serve as the computational degrees of freedom (qubits). The strong dot confinement leads to a strong renormalization of excitonic states, which, in analogy to NMR-based implementations of quantum-information processing, can be exploited for performing conditional and unconditional qubit operations.

cond-mat.mes-hall↗

arXiv2000

Coherent population transfer in coupled semiconductor quantum dots

We propose a solid-state implementation of stimulated Raman adiabatic passage in two coupled semiconductor quantum dots. Proper combination of two pulsed laser fields allows the coherent carrier transfer between the two nanostructures without suffering significant losses due to environment coupling. By use of a general solution scheme for the carrier states in the double-dot structure, we identify the pertinent dot and laser parameters.

cond-mat.mes-hall↗

arXiv2000

Exploiting exciton-exciton interactions in semiconductor quantum dots for quantum-information processing

We propose an all-optical implementation of quantum-information processing in semiconductor quantum dots, where electron-hole excitations (excitons) serve as the computational degrees of freedom (qubits). We show that the strong dot confinement leads to an overall enhancement of Coulomb correlations and to a strong renormalization of the excitonic states, which can be exploited for performing conditional and unconditional qubit operations.

quant-ph↗

arXiv2000

Role of Coulomb correlations in the optical spectra of semiconductor quantum dots

We present a consistent theoretical description of few-particle effects in the optical spectra of semiconductor quantum dots, based on a direct-diagonalization approach. We show that, because of the strong Coulomb interaction among electrons and holes, each configuration of the confined few-particle system leads to its characteristic signature in the optical spectra. We discuss quantitative predictions and comparison with experiments for both absorption and luminescence.

cond-mat.mes-hall↗

arXiv2000

Few-Particle Effects in Semiconductor Quantum Dots: Observation of Multi-Charged-Excitons

We investigate experimentally and theoretically few-particle effects in the optical spectra of single quantum dots (QDs). Photo-depletion of the QD together with the slow hopping transport of impurity-bound electrons back to the QD are employed to efficiently control the number of electrons present in the QD. By investigating structurally identical QDs, we show that the spectral evolutions observed can be attributed to intrinsic, multi-particle-related effects, as opposed to extrinsic QD-impurity environment-related interactions. From our theoretical calculations we identify the distinct transitions related to excitons and excitons charged with up to five additional electrons, as well as neutral and charged biexcitons.

cond-mat.mes-hall↗

arXiv1998

Coulomb correlation effects in semiconductor quantum dots: The role of dimensionality

We study the energy spectra of small three-dimensional (3D) and two-dimensional (2D) semiconductor quantum dots through different theoretical approaches (single-site Hubbard and Hartree-Fock hamiltonians); in the smallest dots we also compare with exact results. We find that purely 2D models often lead to an inadequate description of the Coulomb interaction existing in realistic structures, as a consequence of the overestimated carrier localization. We show that the dimensionality of the dots has a crucial impact on (i) the accuracy of the predicted addition spectra; (ii) the range of validity of approximate theoretical schemes. When applied to realistic 3D geometries, the latter are found to be much more accurate than in the corresponding 2D cases for a large class of quantum dots; the single-site Hubbard hamiltonian is shown to provide a very effective and accurate scheme to describe quantum dot spectra, leading to good agreement with experiments.

cond-mat.mes-hall↗

arXiv1997

Addition energies in semiconductor quantum dots: Role of electron-electron interaction

We show that the addition spectra of semiconductor quantum dots in the presence of magnetic field can be studied through a theoretical scheme that allows an accurate and practical treatment of the single particle states and electron-electron interaction up to large numbers of electrons. The calculated addition spectra exhibit the typical structures of Hund-like shell filling, and account for recent experimental findings. A full three dimensional description of Coulomb interaction is found to be essential for predicting the conductance characteristics of few-electron semiconductor structures.

cond-mat.mes-hall↗

arXiv1997

Coulomb-correlation effects on the non-linear optical properties of realistic quantum wires

We review recent results on the linear and non-linear optical response of realistic quantum-wire structures. Our theoretical approach is based on a set of generalized semiconductor Bloch equations, and allows a full three-dimensional multisubband description of Coulomb correlation for any shape of the confinement profile, thus permitting a direct comparison with experiments for available state-of-the-art wire structures. Our results show that electron-hole Coulomb correlation removes the one-dimensional band-edge singularities from the absorption spectra, whose shape results to be heavily modified with respect to the ideal free-particle case over the whole range of photoexcited carrier densities.

cond-mat.mtrl-sci↗