Publications (27)92.79 Total impact
-
Article: Coherent edge mixing and interferometry in quantum Hall bilayers
[show abstract] [hide abstract]
ABSTRACT: We discuss the implementation of a beam splitter for electron waves in a quantum Hall bilayer. Our architecture exploits inter-layer tunneling to mix edge states belonging to di?erent layers. We discuss the basic working principle of the proposed coherent edge mixer, possible interferometric implementations based on existing semiconductor-heterojunction technologies, and advantages with respect to canonical quantum Hall interferometers based on quantum point contacts.12/2012; -
Article: Imaging backscattering through impurity-induced antidots in quantum Hall constrictions
[show abstract] [hide abstract]
ABSTRACT: We exploit the biased tip of a scanning gate microscope (SGM) to induce a controlled backscattering between counter-propagating edge channels in a wide constriction in the quantum Hall regime. We compare our detailed conductance maps with a numerical percolation model and demonstrate that conductance fluctuations observed in these devices as a function of the gate voltage originate from backscattering events mediated by localized states pinned by potential fluctuations. Our imaging technique allows us to identify the necessary conditions for the activation of these backscattering processes and also to reconstruct the constriction confinement potential profile and the underlying disorder.09/2012; -
Article: Electrostatic Spin Control in InAs/InP Nanowire Quantum Dots.
[show abstract] [hide abstract]
ABSTRACT: Very robust voltage-controlled spin transitions in few-electron quantum dots are demonstrated. Two lateral-gate electrodes patterned on opposite sides of an InAs/InP nanowire are used to apply a transverse electric field and tune orbital energy separation down to level-pair degeneracy. Transport measurements in this regime allow us to demonstrate the breakdown of the standard alternate up/down spin filling scheme and unambiguously show singlet-triplet spin transitions. The strong confinement of the present devices leads to a large energy gain for the observed anomalous spin configurations that exceeds 4 meV. As a consequence, this behavior is well visible even at temperatures exceeding T = 20 K.Nano Letters 07/2012; 12(9):4490-4. · 13.20 Impact Factor -
Article: Imaging fractional incompressible stripes in integer quantum Hall systems
[show abstract] [hide abstract]
ABSTRACT: Transport experiments provide conflicting evidence on the possible existence of fractional order within integer quantum Hall systems. In fact integer edge states sometimes behave as monolithic objects with no inner structure, while other experiments clearly highlight the role of fractional substructures. Recently developed low-temperature scanning probe techniques offer today an opportunity for a deeper-than-ever investigation of spatial features of such edge systems. Here we use scanning gate microscopy and demonstrate that fractional features were unambiguously observed in every integer quantum Hall constriction studied. We present also an experimental estimate of the width of the fractional incompressible stripes corresponding to filling factors 1/3, 2/5, 3/5, and 2/3. Our results compare well with predictions of the edge-reconstruction theory.05/2012; -
Article: Hot-electron effects in InAs nanowire Josephson junctions
[show abstract] [hide abstract]
ABSTRACT: The controlled tailoring of the energy distribution in an electron system opens the way to interesting new physics and device concepts, as demonstrated by research on metallic nanodevices during recent years. Here we investigate how Josephson coupling in a superconductor-InAs nanowire junction can be tuned by means of hot-electron injection and we show that a complete suppression of superconductive effects can be achieved using a power as low as 100 pW. Nanowires offer a novel design freedom as they allow axial and radial heterostructures to be defined as well as control over doping profiles, which can be crucial in the development of devices—such as nanorefrigerators—where precisely controlled and predictable energy barriers are mandatory. Our work provides estimates for unknown key thermal and electrical parameters, such as the electron-phonon coupling, in our InAs nanostructures. KeywordsNanowire–hot-electron–Josephson effect–InAs–heat conductionNano Research 04/2012; 4(3):259-265. · 6.97 Impact Factor -
Article: Impact of electron heating on the equilibration between quantum Hall edge channels
[show abstract] [hide abstract]
ABSTRACT: When two separately contacted quantum Hall (QH) edge channels are brought into interaction, they can equilibrate their imbalance via scattering processes. In the present work we use a tunable QH circuit to implement a junction between co-propagating edge channels whose length can be controlled with continuity. Such a variable device allows us to investigate how current-voltage characteristics evolve when the junction length d is changed. Recent experiments with fixed geometry reported a significant reduction of the threshold voltage for the onset of photon emission, whose origin is still under debate. Our spatially resolved measurements reveal that this threshold shift depends on the junction length. We discuss this unexpected result on the basis of a model which demonstrates that a heating of electrons is the dominant process responsible for the observed reduction of the threshold voltage.12/2011; -
Article: Controlled coupling of spin-resolved quantum Hall edge states.
[show abstract] [hide abstract]
ABSTRACT: We introduce and experimentally demonstrate a new method that allows us to controllably couple copropagating spin-resolved edge states of a two-dimensional electron gas (2DEG) in the integer quantum Hall regime. The scheme exploits a spatially periodic in-plane magnetic field that is created by an array of Cobalt nanomagnets placed at the boundary of the 2DEG. A maximum charge or spin transfer of 28±1% is achieved at 250 mK.Physical Review Letters 12/2011; 107(23):236804. · 7.37 Impact Factor -
Article: Controlled coupling of spin-resolved quantum Hall edge states
[show abstract] [hide abstract]
ABSTRACT: Topologically-protected edge states are dissipationless conducting surface states immune to impurity scattering and geometrical defects that occur in electronic systems characterized by a bulk insulating gap. One example can be found in a two-dimensional electron gas (2DEG) under high magnetic field in the quantum Hall regime. Based on the coherent control of the coupling between these protected states, several theoretical proposals for the implementation of information processing architectures were proposed. Here we introduce and experimentally demonstrate a new method that allows us to controllably couple co-propagating spin-resolved edge states of a QH insulator. The scheme exploits a spatially-periodic in-plane magnetic field that is created by an array of Cobalt nano-magnets placed at the boundary of the 2DEG. A maximum charge/spin transfer of about 28% is achieved at 250 mK. This result may open the way to the realization of scalable quantum-information architectures exploiting the spin degree of freedom of topologically-protected states.06/2011; -
Article: Self-assembly and electron-beam-induced direct etching of suspended graphene nanostructures
[show abstract] [hide abstract]
ABSTRACT: We report on suspended single-layer graphene deposition by a transfer-printing approach based on polydimethylsiloxane stamps. The transfer printing method allows the exfoliation of graphite flakes from a bulk graphite sample and their residue-free deposition on a silicon dioxide substrate. This deposition system creates a blistered graphene surface due to strain induced by the transfer process itself. Single-layer-graphene deposition and its "blistering" on the substrate are demonstrated by a combination of Raman spectroscopy, scanning electron microscopy and atomic-force microscopy measurements. Finally, we demonstrate that blister-like suspended graphene are self-supporting single-layer structures and can be flattened by employing a spatially-resolved direct-lithography technique based on electron-beam induced etching.05/2011; -
Article: Manipulation of electron orbitals in hard-wall InAs/InP nanowire quantum dots.
[show abstract] [hide abstract]
ABSTRACT: We present a novel technique for the manipulation of the energy spectrum of hard-wall InAs/InP nanowire quantum dots. By using two local gate electrodes, we induce a strong transverse electric field in the dot and demonstrate the controlled modification of its electronic orbitals. Our approach allows us to dramatically enhance the single-particle energy spacing between the first two quantum levels in the dot and thus to increment the working temperature of our InAs/InP single-electron transistors. Our devices display a very robust modulation of the conductance even at liquid nitrogen temperature, while allowing an ultimate control of the electron filling down to the last free carrier. Potential further applications of the technique to time-resolved spin manipulation are also discussed.Nano Letters 03/2011; 11(4):1695-9. · 13.20 Impact Factor -
Article: Spatially-resolved analysis of edge-channel equilibration in quantum Hall circuits
[show abstract] [hide abstract]
ABSTRACT: We demonstrate an innovative quantum Hall circuit with variable geometry employing the moveable electrostatic potential induced by a biased atomic force microscope tip. We exploit this additional degree of freedom to identify the microscopic mechanisms that allow two co-propagating edge channels to equilibrate their charge imbalance. Experimental results are compared with tight-binding simulations based on a realistic model for the disorder potential. This work provides also an experimental realization of a beam mixer between co-propagating edge channels, a still elusive building block of a recently proposed new class of quantum interferometers.02/2011; -
Article: Probing the gate--voltage-dependent surface potential of individual InAs nanowires using random telegraph signals.
[show abstract] [hide abstract]
ABSTRACT: We report a novel method for probing the gate-voltage dependence of the surface potential of individual semiconductor nanowires. The statistics of electronic occupation of a single defect on the surface of the nanowire, determined from a random telegraph signal, is used as a measure for the local potential. The method is demonstrated for the case of one or two switching defects in indium arsenide (InAs) nanowire field effect transistors at temperatures T=25-77 K. Comparison with a self-consistent model shows that surface potential variation is retarded in the conducting regime due to screening by surface states with density Dss≈10(12) cm(-2) eV(-1). Temperature-dependent dynamics of electron capture and emission producing the random telegraph signals are also analyzed, and multiphonon emission is identified as the process responsible for capture and emission of electrons from the surface traps. Two defects studied in detail had capture activation energies of EB≈50 meV and EB≈110 meV and cross sections of σ∞≈3×10(-19) cm2 and σ∞≈2×10(-17) cm2, respectively. A lattice relaxation energy of Sℏω=187±15 meV was found for the first defect.ACS Nano 02/2011; 5(3):2191-9. · 10.77 Impact Factor -
Article: InAs/InSb nanowire heterostructures grown by chemical beam epitaxy.
[show abstract] [hide abstract]
ABSTRACT: We report the Au-assisted chemical beam epitaxy growth of defect-free zincblende InSb nanowires. The grown InSb segments are the upper sections of InAs/InSb heterostructures on InAs(111)B substrates. We show, through HRTEM analysis, that zincblende InSb can be grown without any crystal defects such as stacking faults or twinning planes. Strain-map analysis demonstrates that the InSb segment is nearly relaxed within a few nanometers from the interface. By post-growth studies we have found that the catalyst particle composition is AuIn(2), and it can be varied to a AuIn alloy by cooling down the samples under TDMASb flux.Nanotechnology 11/2009; 20(50):505605. · 3.98 Impact Factor -
Article: Growth of vertical InAs nanowires on heterostructured substrates.
[show abstract] [hide abstract]
ABSTRACT: We investigate the Au-assisted growth of InAs nanowires on two different kinds of heterostructured substrates: GaAs/AlGaAs structures capped by a 50 nm thick InAs layer grown by molecular beam epitaxy and a 2 microm thick InAs buffer layer on Si(111) obtained by vapor phase epitaxy. Morphological and structural properties of substrates and nanowires are analyzed by atomic force and transmission electron microscopy. Our results indicate a promising direction for the integration of III-V nanostructures on Si-based electronics as well as for the development of novel micromechanical structures incorporating nanowires as their active elements.Nanotechnology 08/2009; 20(28):285303. · 3.98 Impact Factor -
Article: Tuning nonlinear charge transport between integer and fractional quantum Hall states.
[show abstract] [hide abstract]
ABSTRACT: Controllable point junctions between different quantum Hall phases are a necessary building block for the development of mesoscopic circuits based on fractionally charged quasiparticles. We demonstrate how particle-hole duality can be exploited to realize such point-contact junctions. We show an implementation for the case of two quantum Hall liquids at filling factors nu=1 and nu*<or=1 in which both the fractional filling nu* and the coupling strength can be finely and independently tuned. A peculiar crossover from insulating to conducting behavior as nu* goes from 1/3 to 1 is observed. These results highlight the key role played on interedge tunneling by local charge depletion at the point contact.Physical Review Letters 07/2009; 103(1):016802. · 7.37 Impact Factor -
Article: Tuning non-linear charge transport between integer and fractional quantum Hall states
[show abstract] [hide abstract]
ABSTRACT: Controllable point junctions between different quantum Hall phases are a necessary building block for the development of mesoscopic circuits based on fractionally-charged quasiparticles. We demonstrate how particle-hole duality can be exploited to realize such point-contact junctions. We show an implementation for the case filling factors $\nu=1$ and $\nu^*\le1$ in which both the fractional filling $\nu^*$ and the coupling strength can be finely and independently tuned. A peculiar crossover from insulating to conducting behavior as $\nu^*$ goes from 1/3 to 1 is observed. These results highlight the key role played on inter-edge tunneling by local charge depletion at the point contact. Comment: 4 pages, 3 figures, suppl.mat03/2009; -
Article: Controlled growth of InAs nanowires on engineered substrates
[show abstract] [hide abstract]
ABSTRACT: We demonstrate the Au-assisted growth of semiconductor nanowires on different engineered substrates. Two relevant cases are investigated: GaAs/AlGaAs heterostructures capped by a $50 {\rm nm}$-thick InAs layer grown by molecular beam epitaxy and a $2 {\rm \mu m}$-thick InAs buffer layer on Si(111) obtained by vapor phase epitaxy. Morphological and structural properties of substrates and nanowires are analyzed by atomic force and transmission electron microscopy. Our results indicate a promising direction for the integration of III-V nanostructures on Si-based electronics as well as for the development of novel micromechanical structures. Comment: 5 pages, 5 figures, suppl.mat03/2009; -
Article: InAs Nanowire MOS Capacitors
[show abstract] [hide abstract]
ABSTRACT: We present a capacitance-voltage study for arrays of vertical InAs nanowires. MOS capacitors are obtained by insulating the nanowires with a conformal 10nm HfO2 layer and using a top Cr/Au metallization as one of the capacitor's electrodes. The described fabrication and characterization technique enables a systematic investigation of the carrier density in the nanowires as well as of the quality of the MOS interface.07/2008; -
Article: InAs nanowire metal-oxide-semiconductor capacitors
[show abstract] [hide abstract]
ABSTRACT: We present a capacitance-voltage study for arrays of vertical InAs nanowires. Metal-oxide-semiconductor (MOS) capacitors are obtained by insulating the nanowires with a conformal 10 nm HfO2 layer and using a top Cr/Au metallization as one of the capacitor’s electrodes. The described fabrication and characterization technique enables a systematic investigation of the carrier density in the nanowires as well as of the quality of the MOS interface.Applied Physics Letters 06/2008; 92(25):253509-253509-3. · 3.84 Impact Factor -
Article: Particle-hole symmetric Luttinger liquids in a quantum Hall circuit.
[show abstract] [hide abstract]
ABSTRACT: We report current transmission data through a split-gate constriction fabricated onto a two-dimensional electron system in the integer quantum Hall (QH) regime. Split-gate biasing drives interedge backscattering and is shown to lead to suppressed or enhanced transmission, in marked contrast to the expected linear Fermi-liquid behavior. This evolution is described in terms of particle-hole symmetry and allows us to conclude that an unexpected class of gate-controlled particle-hole-symmetric chiral Luttinger liquids (CLLs) can exist at the edges of our QH circuit. These results highlight the role of particle-hole symmetry on the properties of CLL edge states.Physical Review Letters 11/2005; 95(15):156804. · 7.37 Impact Factor
Top co-authors
Top Journals
- Physical Review Letters (4)
- Nanotechnology (2)
- Nano Letters (2)
- Applied Physics Letters (1)
- Physical Review Letters (1)
Institutions
-
2003–2012
-
Scuola Normale Superiore di Pisa
Pisa, Tuscany, Italy
-
-
2008
-
Lund University
- Division of Solid State Physics
Lund, Skane, Sweden
-
