V. Pellegrini

Publications (41)124.19 Total impact

• Article: A ballistic quantum ring Josephson interferometer.

  A Fornieri, M Amado, F Carillo, F Dolcini, G Biasiol, L Sorba, V Pellegrini, F Giazotto
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  ABSTRACT: We report the realization of a ballistic Josephson interferometer. The interferometer is made from a quantum ring etched in a nanofabricated two-dimensional electron gas confined in an InAs-based heterostructure laterally contacted to superconducting niobium leads. The Josephson current flowing through the structure shows oscillations with h/e flux periodicity when threading the loop with a perpendicular magnetic field. This periodicity, in sharp contrast with the h/2e one observed in conventional dc superconducting quantum interference devices, confirms the ballistic nature of the device in agreement with theoretical predictions. This system paves the way for the implementation of interferometric Josephson π-junctions, and for the investigation of Majorana fermions.
  Nanotechnology 05/2013; 24(24):245201. · 3.98 Impact Factor
• Article: Electrostatic tailoring of magnetic interference in quantum point contact ballistic Josephson junctions

  M. Amado, A. Fornieri, F. Carillo, G. Biasiol, L. Sorba, V. Pellegrini, F. Giazotto
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  ABSTRACT: The magneto-electrostatic tailoring of the supercurrent in quantum point contact ballistic Josephson junctions is demonstrated. An etched InAs-based heterostructure is laterally contacted to superconducting niobium leads and the existence of two etched side gates permits, in combination with the application of a perpendicular magnetic field, to modify continuously the magnetic interference pattern by depleting the weak link. For wider junctions the supercurrent presents a Fraunhofer-like interference pattern with periodicity h/2e whereas by shrinking electrostatically the weak link, the periodicity evolves continuously to a monotonic decay. These devices represent novel tunable structures that might lead to the study of the elusive Majorana fermions.
  02/2013;
• Article: Spin transition in the fractional quantum Hall regime: Effect of extent of the wave function

  V. V. Vanovsky, V. S. Khrapai, A. A. Shashkin, V. Pellegrini, L. Sorba, G. Biasiol
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  ABSTRACT: Using a magnetocapacitance technique, we determine the magnetic field of the spin transition, B*, at filling factor nu=2/3 in the 2D electron system in GaAs/AlGaAs heterojunctions. The field B* is found to decrease appreciably as the wave function extent controlled by back gate voltage is increased. Our calculations show that the contributions to the shift of B* from the change of the Coulomb energy and the g factor change due to nonparabolicity are approximately the same. The observed relative shift of B* is described with no fitting parameters.
  10/2012;
• Article: Graphene field-effect transistors as room-temperature terahertz detectors.

  L Vicarelli, M S Vitiello, D Coquillat, A Lombardo, A C Ferrari, W Knap, M Polini, V Pellegrini, A Tredicucci
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  ABSTRACT: The unique optoelectronic properties of graphene make it an ideal platform for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic modules, optical modulators, plasmonic devices, microcavities, and ultra-fast lasers. Owing to its high carrier mobility, gapless spectrum and frequency-independent absorption, graphene is a very promising material for the development of detectors and modulators operating in the terahertz region of the electromagnetic spectrum (wavelengths in the hundreds of micrometres), still severely lacking in terms of solid-state devices. Here we demonstrate terahertz detectors based on antenna-coupled graphene field-effect transistors. These exploit the nonlinear response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature operation at 0.3 THz, showing that our devices can already be used in realistic settings, enabling large-area, fast imaging of macroscopic samples.
  Nature Material 09/2012; 11(10):865-71. · 32.84 Impact Factor
• Source

  Available from: Giorgio Biasiol

  Article: Influence of e-e scattering on the temperature dependence of the resistance of a classical ballistic point contact in a two-dimensional electron system

  M. Yu. Melnikov, J. P. Kotthaus, V. Pellegrini, L. Sorba, G. Biasiol, V. S. Khrapai
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  ABSTRACT: We experimentally investigate the temperature (T) dependence of the resistance of a classical ballistic point contact (PC) in a two-dimensional electron system (2DES). The split-gate PC is realized in a high-quality AlGaAs/GaAs heterostructure. The PC resistance is found to drop by more than 10% as T is raised from 0.5 K to 4.2 K. In the absence of a magnetic field, the T dependence is roughly linear below 2 K and tends to saturate at higher T. Perpendicular magnetic fields on the order of a few 10 mT suppress the T-dependent contribution dR. This effect is more pronounced at lower temperatures, causing a crossover to a nearly parabolic T dependence in a magnetic field. The normalized magnetic field dependencies dR(B) permit an empiric single parameter scaling in a wide range of PC gate voltages. These observations give strong evidence for the influence of electron-electron (e-e) scattering on the resistance of ballistic PCs. Our results are in qualitative agreement with a recent theory of the e-e scattering based T dependence of the conductance of classical ballistic PCs [ Phys. Rev. Lett. 101 216807 (2008) and Phys. Rev. B 81 125316 (2010)].
  02/2012;
• Article: Atomic and electronic structure of zerolayer and quasi-free standing monolayer graphene on SiC(0001)

  S. Goler, C. Coletti, V. Pellegrini, K. V. Emtsev, U. Starke, F. Beltram, S. Heun
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  ABSTRACT: Graphene epitaxially grown on the silicon face of silicon carbide resides on top of a carbon layer, known as zerolayer graphene. This layer is in part covalently bound to the SiC substrate and its structural and electronic properties are controversially debated. In the present work we report scanning tunnelling microscopy (STM) studies of zerolayer epitaxially grown on SiC(0001), and of the zerolayer decoupled from the substrate by hydrogen intercalation, the so called quasi-free standing monolayer graphene (QFMLG). Notably, atomically-resolved STM images of the zerolayer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of the atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no obvious defective sites.
  11/2011;
• Source

  Available from: Shengjun Yuan

  Article: Two-dimensional Mott-Hubbard electrons in an artificial honeycomb lattice.

  A Singha, M Gibertini, B Karmakar, S Yuan, M Polini, G Vignale, M I Katsnelson, A Pinczuk, L N Pfeiffer, K W West, V Pellegrini
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  ABSTRACT: Artificial crystal lattices can be used to tune repulsive Coulomb interactions between electrons. We trapped electrons, confined as a two-dimensional gas in a gallium arsenide quantum well, in a nanofabricated lattice with honeycomb geometry. We probed the excitation spectrum in a magnetic field, identifying collective modes that emerged from the Coulomb interaction in the artificial lattice, as predicted by the Mott-Hubbard model. These observations allow us to determine the Hubbard gap and suggest the existence of a Coulomb-driven ground state.
  Science 06/2011; 332(6034):1176-9. · 31.20 Impact Factor
• Source

  Available from: Francesco Giazotto

  Article: Quantum dot spectroscopy of proximity-induced superconductivity in a two-dimensional electron gas

  F. Deon, V. Pellegrini, F. Giazotto, G. Biasiol, L. Sorba, F. Beltram
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  ABSTRACT: We report the realization of a hybrid superconductor-quantum dot device by means of top-down nanofabrication starting from a two-dimensional electron gas in a InGaAs/InAlAs semiconductor heterostructure. The quantum dot is defined by electrostatic gates placed within the normal region of a planar Nb–InGaAs quantum well-Nb junction. Measurements in the regime of strong Coulomb blockade as well as cotunneling spectroscopy allow to directly probe the proximity-induced energy gap in a ballistic two-dimensional electron gas coupled to superconductors.
  Applied Physics Letters 03/2011; 98(13):132101-132101-3. · 3.84 Impact Factor
• Source

  Available from: ArXiv

  Article: Observation of magneto-phonon resonance of Dirac fermions in graphite

  J. Yan, S. Goler, T. D. Rhone, M. Han, R. He, P. Kim, V. Pellegrini, A. Pinczuk
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  ABSTRACT: Coherent coupling of Dirac fermion magneto-excitons with an optical phonon is observed in graphite as marked magnetic-field dependent splittings and anti-crossing behavior of the two coupled modes. The sharp magneto-phonon resonance occurs in regions of the graphite sample with properties of superior single-layer graphene having enhanced lifetimes of Dirac fermions. The greatly reduced carrier broadening to values below the graphene electron-phonon coupling constant explains the appearance of sharp resonances that reveal a fundamental interaction of Dirac fermions. Comment: 5 figures, supplementary material section included
  08/2010;
• Source

  Available from: Giorgio De Simoni

  Article: Delocalized-localized transition in a semiconductor two-dimensional honeycomb lattice

  G. De Simoni, A. Singha, M. Gibertini, B. Karmakar, M. Polini, V. Piazza, L. N. Pfeiffer, K. W. West, F. Beltram, V. Pellegrini
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  ABSTRACT: We report the magneto-transport properties of a two-dimensional electron gas in a modulation-doped AlGaAs/GaAs heterostructure subjected to a lateral potential with honeycomb geometry. Periodic oscillations of the magneto-resistance and a delocalized-localized transition are shown by applying a gate voltage. We argue that electrons in such artificial-graphene lattices offer a promising approach for the simulation of quantum phases dictated by Coulomb interactions.
  07/2010;
• Source

  Available from: F. Carillo

  Article: Singlet-triplet transition in a few-electron lateral InGaAs-InAlAs quantum dot

  F. Deon, V. Pellegrini, F. Carillo, F. Giazotto, L. Sorba, G. Biasiol, F. Beltram
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  ABSTRACT: The magnetic-field evolution of Coulomb blockade peaks in lateral InGaAs/InAlAs quantum dots in the few-electron regime is reported. Quantum dots are defined by gates evaporated onto a 60 nm-thick hydrogen silsesquioxane insulating film. A gyromagnetic factor of 4.4 is measured via zero-bias spin spectroscopy and a transition from singlet to triplet spin configuration is found at an in-plane magnetic field B = 0.7 T. This observation opens the way to the manipulation of singlet and triplet states at moderate fields and its relevance for quantum information applications will be discussed. Comment: 4 pages, 3 figures
  02/2010;
• Article: Singlet-triplet transition in a few-electron lateral In0.75 Ga0.25 As/ In0.75 Al0.25 As quantum dot

  F Deon, V Pellegrini, F Carillo, F Giazotto, G Biasiol, L Sorba, F Beltram
  Applied Physics Letters 01/2010; 96(14). · 3.84 Impact Factor
• Source

  Available from: ArXiv

  Article: Engineering artificial graphene in a two-dimensional electron gas

  M. Gibertini, A. Singha, V. Pellegrini, M. Polini, G. Vignale, A. Pinczuk, L. N. Pfeiffer, K. W. West
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  ABSTRACT: At low energy, electrons in doped graphene sheets behave like massless Dirac fermions with a Fermi velocity which does not depend on carrier density. Here we show that modulating a two-dimensional electron gas with a long-wavelength periodic potential with honeycomb symmetry can lead to the creation of isolated massless Dirac points with tunable Fermi velocity. We provide detailed theoretical estimates to realize such artificial graphene-like system and discuss an experimental realization in a modulation-doped GaAs quantum well. Ultra high-mobility electrons with linearly-dispersing bands might open new venues for the studies of Dirac-fermion physics in semiconductors. Comment: 4 + epsilon pages, 3 figures, submitted to PRB
  04/2009;
• Article: Probing collective modes of correlated states of few electrons in semiconductor quantum dots

  S. Kalliakos, M. Rontani, V. Pellegrini, A. Pinczuk, A. Shinga, C. P. Garcia, G. Goldoni, E. Molinari, L. N. Pfeiffer, K. W. West
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  ABSTRACT: A review. Low-lying collective excitations above highly correlated ground states of few interacting electrons confined in GaAs semiconductor quantum dots are probed by resonant inelastic light scattering. We highlight that sep. studies of the changes in the spin and charge degrees of freedom offer unique access to the fundamental interactions. The case of quantum dots with four electrons is found to be detd. by a competition between triplet and singlet ground states that is uncovered in the rich light scattering spectra of spin excitations. These light scattering results are described within a configuration-interaction framework that captures the role of electron correlation with quant. accuracy. Recent light scattering results that reveal the impact of anisotropic confining potentials in laterally coupled quantum dots are also reviewed. In these studies, inelastic light scattering methods emerge as powerful probes of collective phenomena and spin configurations in quantum dots with few electrons. [on SciFinder (R)]
  Solid State Commun. 01/2009; 149:1436-1442.
• Source

  Available from: Giorgio Biasiol

  Article: Filling factor dependence of the fractional quantum Hall effect gap.

  V S Khrapai, A A Shashkin, M G Trokina, V T Dolgopolov, V Pellegrini, F Beltram, G Biasiol, L Sorba
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  ABSTRACT: We directly measure the chemical potential jump in the low-temperature limit when the filling factor traverses the nu=1/3 and nu=2/5 fractional gaps in two-dimensional (2D) electron system in GaAs/AlGaAs single heterojunctions. In high magnetic fields B, both gaps are linear functions of B with slopes proportional to the inverse fraction denominator, 1/q. The fractional gaps close partially when the Fermi level lies outside. An empirical analysis indicates that the chemical potential jump for an ideal 2D electron system, in the highest accessible magnetic fields, is proportional to q(-1) B(1/2).
  Physical Review Letters 05/2008; 100(19):196805. · 7.37 Impact Factor
• Article: The optical visibility of graphene: interference colors of ultrathin graphite on SiO(2).

  S Roddaro, P Pingue, V Piazza, V Pellegrini, F Beltram
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  ABSTRACT: Monatomic layers of graphite are emerging as building blocks for novel optoelectronic devices. Experimental studies on a single graphite layer (graphene) are today possible since very thin graphite can be identified on a dielectric substrate using a normal optical microscope. We investigate the mechanism behind the strong visibility of graphite, and we discuss the importance of substrates and of the microscope objective used for the imaging.
  Nano Letters 10/2007; 7(9):2707-10. · 13.20 Impact Factor
• Source

  Available from: Giorgio Biasiol

  Article: Direct measurements of fractional quantum Hall effect gaps.

  V S Khrapai, A A Shashkin, M G Trokina, V T Dolgopolov, V Pellegrini, F Beltram, G Biasiol, L Sorba
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  ABSTRACT: We measure the chemical potential jump across the fractional gap in the low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs single heterojunctions. In the fully spin-polarized regime, the gap for filling factor nu=1/3 increases linearly with the magnetic field and is coincident with that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau level. In low magnetic fields, at the ground-state spin transition for nu=2/3, a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed.
  Physical Review Letters 09/2007; 99(8):086802. · 7.37 Impact Factor
• Source

  Available from: Pasqualantonio Pingue

  Article: Colors Of Graphite On Silicon Dioxide

  S. Roddaro, P. Pingue, V. Piazza, V. Pellegrini, F. Beltram
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  ABSTRACT: Monoatomic layers of graphite can be electrically contacted and used as building blocks for new promising devices. These experiment are today possible thanks to the fact that very thin graphite can be identified on a dielectric substrate using a simple optical microscope. We investigate the mechanism behind the strong visibility of graphite and we discuss the importance of the substrate and of the microcope objective used for the imaging.
  06/2007;
• Source

  Available from: Stefano Luin

  Article: Resonant Rayleigh scattering from quantum phases of cold electrons in semiconductor heterostructures

  S. Luin, V. Pellegrini, A. Pinczuk, B. S. Dennis, L. N. Pfeiffer, K. W. West
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  ABSTRACT: Resonant Rayleigh scattering of light from electrons confined in gallium arsenide double quantum wells displays significant changes at temperatures that are below one degree Kelvin. The Rayleigh resonance occurs for photon energies that overlap a quantum well exciton and when electron bilayers condense into a quantum-Hall state. Marked changes in Rayleigh scattering intensities that occur in response to application of an in-plane magnetic field indicate that the unexpected temperature dependence is linked to formation of non-uniform electron fluids in a disordered quantum-Hall phase. These results demonstrate a new realm of study in which resonant Rayleigh scattering methods probe quantum phases of cold electrons in semiconductor heterostructures.
  07/2006;
• Article: Inelastic light scattering by low-lying excitations of electrons in low-dimensional semiconductors

  V. Pellegrini, A. Pinczuk
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  ABSTRACT: The low-dimensional electron systems that reside in artificial semiconductor heterostructures of great perfection are a contemporary materials base for explorations of collective phenomena. Studies of low-lying elementary excitations by inelastic light scattering offer insights on properties such energetics, interactions and spin magnetization. We review here recent light scattering results obtained from two-dimensional (2D) quantum fluids in semiconductor heterostructures under extreme conditions of low temp. and large magnetic field, where the quantum Hall phases are archetypes of novel behaviors. We also consider recent light scattering expts. that have probed the excitation spectra of few-electron states in semiconductor quantum dots. [on SciFinder (R)]
  Physica Status Solidi B: Basic Solid State Physics. 01/2006; 243:3617-3628.