ORCID Profile
0000-0003-2668-2401
Current Organisation
Hitachi Cambridge Laboratory
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Publisher: Springer Science and Business Media LLC
Date: 09-2201
DOI: 10.1038/NCOMMS1038
Abstract: In the quantum Hall regime, near integer filling factors, electrons should only be transmitted through spatially separated edge states. However, in mesoscopic systems, electronic transmission turns out to be more complex, giving rise to a large spectrum of magnetoresistance oscillations. To explain these observations, recent models put forward the theory that, as edge states come close to each other, electrons can hop between counterpropagating edge channels, or tunnel through Coulomb islands. Here, we use scanning gate microscopy to demonstrate the presence of QH Coulomb islands, and reveal the spatial structure of transport inside a QH interferometer. Locations of electron islands are found by modulating the tunnelling between edge states and confined electron orbits. Tuning the magnetic field, we unveil a continuous evolution of active electron islands. This allows to decrypt the complexity of high-magnetic-field magnetoresistance oscillations, and opens the way to further local-scale manipulations of QH localized states.
Publisher: Springer Science and Business Media LLC
Date: 11-03-2013
DOI: 10.1038/SREP01416
Abstract: The unique properties of quantum hall devices arise from the ideal one-dimensional edge states that form in a two-dimensional electron system at high magnetic field. Tunnelling between edge states across a quantum point contact (QPC) has already revealed rich physics, like fractionally charged excitations, or chiral Luttinger liquid. Thanks to scanning gate microscopy, we show that a single QPC can turn into an interferometer for specific potential landscapes. Spectroscopy, magnetic field and temperature dependences of electron transport reveal a quantitatively consistent interferometric behavior of the studied QPC. To explain this unexpected behavior, we put forward a new model which relies on the presence of a quantum Hall island at the centre of the constriction as well as on different tunnelling paths surrounding the island, thereby creating a new type of interferometer. This work sets the ground for new device concepts based on coherent tunnelling.
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4848369
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4848404
Publisher: American Physical Society (APS)
Date: 28-03-2016
Publisher: American Physical Society (APS)
Date: 28-03-2019
Publisher: American Physical Society (APS)
Date: 10-03-2008
Publisher: American Physical Society (APS)
Date: 18-05-2005
Publisher: American Physical Society (APS)
Date: 31-03-2022
Publisher: American Physical Society (APS)
Date: 24-03-2022
Publisher: Springer Science and Business Media LLC
Date: 03-06-2021
Publisher: American Physical Society (APS)
Date: 25-11-2014
Publisher: Springer Science and Business Media LLC
Date: 30-06-2014
DOI: 10.1038/NCOMMS5290
Abstract: Quantum point contacts exhibit mysterious conductance anomalies in addition to well-known conductance plateaus at multiples of 2e(2)/h. These 0.7 and zero-bias anomalies have been intensively studied, but their microscopic origin in terms of many-body effects is still highly debated. Here we use the charged tip of a scanning gate microscope to tune in situ the electrostatic potential of the point contact. While sweeping the tip distance, we observe repetitive splittings of the zero-bias anomaly, correlated with simultaneous appearances of the 0.7 anomaly. We interpret this behaviour in terms of alternating equilibrium and non-equilibrium Kondo screenings of different spin states localized in the channel. These alternating Kondo effects point towards the presence of a Wigner crystal containing several charges with different parities. Indeed, simulations show that the electron density in the channel is low enough to reach one-dimensional Wigner crystallization over a size controlled by the tip position.
Publisher: American Physical Society (APS)
Date: 30-11-2017
Publisher: American Physical Society (APS)
Date: 17-12-2021
Publisher: AIP
Date: 2003
DOI: 10.1063/1.1639808
Publisher: IOP Publishing
Date: 08-04-2011
Publisher: American Physical Society (APS)
Date: 13-02-2012
Publisher: IOP Publishing
Date: 10-06-2009
DOI: 10.1088/0957-4484/20/26/264021
Abstract: We study scanning gate microscopy (SGM) in open quantum rings obtained from buried semiconductor InGaAs/InAlAs heterostructures. By performing a theoretical analysis based on the Keldysh-Green function approach we interpret the radial fringes observed in experiments as the effect of randomly distributed charged defects. We associate SGM conductance images with the local density of states (LDOS) of the system. We show that such an association cannot be made with the current density distribution. By varying an external magnetic field we are able to reproduce recursive quasi-classical orbits in LDOS and conductance images, which bear the same periodicity as the Aharonov-Bohm effect.
Publisher: Institute of Physics, Polish Academy of Sciences
Date: 05-2011
Publisher: IOP Publishing
Date: 18-01-2013
Publisher: American Physical Society (APS)
Date: 21-03-2018
Publisher: Springer Berlin Heidelberg
Date: 29-08-2013
Publisher: American Physical Society (APS)
Date: 16-03-2016
Publisher: Springer Science and Business Media LLC
Date: 12-11-2006
DOI: 10.1038/NPHYS459
Publisher: American Physical Society (APS)
Date: 25-02-2015
Publisher: American Physical Society (APS)
Date: 28-09-2007
Publisher: AIP Publishing
Date: 23-01-2006
DOI: 10.1063/1.2168251
Abstract: When the tip-s le distance is small, Kelvin probe force microscopy is affected by parametric lification. This is due to the fact that the electric force has two components the higher one having a frequency exactly twice as high as the lower. The oscillation litude may substantially depart from what is usually expected. Those phenomena are analytically modeled and experimentally shown, and the optimal parameter values which must be used for voltage detection are established.
Publisher: Springer Science and Business Media LLC
Date: 14-02-2018
DOI: 10.1038/S41598-018-21250-Y
Abstract: A counter-intuitive behavior analogous to the Braess paradox is encountered in a two-terminal mesoscopic network patterned in a two-dimensional electron system (2DES). Decreasing locally the electron density of one channel of the network paradoxically leads to an increased network electrical conductance. Our low temperature scanning gate microscopy experiments reveal different occurrences of such puzzling conductance variations, thanks to tip-induced localized modifications of electron flow throughout the network’s channels in the ballistic and coherent regime of transport. The robustness of the puzzling behavior is inspected by varying the global 2DES density, magnetic field and the tip-surface distance. Depending on the overall 2DES density, we show that either Coulomb Blockade resonances due to disorder-induced localized states or Fabry-Perot interferences tuned by the tip-induced electrostatic perturbation are at the origin of transport inefficiencies in the network, which are lifted when gradually closing one channel of the network with the tip.
Publisher: American Physical Society (APS)
Date: 31-07-2017
Publisher: American Physical Society (APS)
Date: 28-04-2017
Publisher: Springer Science and Business Media LLC
Date: 03-10-2016
Abstract: Electron spins in gate-defined quantum dots provide a promising platform for quantum computation. In particular, spin-based quantum computing in gallium arsenide takes advantage of the high quality of semiconducting materials, reliability in fabricating arrays of quantum dots and accurate qubit operations. However, the effective magnetic noise arising from the hyperfine interaction with uncontrolled nuclear spins in the host lattice constitutes a major source of decoherence. Low-frequency nuclear noise, responsible for fast (10 ns) inhomogeneous dephasing, can be removed by echo techniques. High-frequency nuclear noise, recently studied via echo revivals, occurs in narrow-frequency bands related to differences in Larmor precession of the three isotopes
Publisher: American Physical Society (APS)
Date: 23-02-2023
Publisher: Springer Science and Business Media LLC
Date: 22-08-2012
Abstract: The Braess paradox, known for traffic and other classical networks, lies in the fact that adding a new route to a congested network in an attempt to relieve congestion can degrade counterintuitively the overall network performance. Recently, we have extended the concept of the Braess paradox to semiconductor mesoscopic networks, whose transport properties are governed by quantum physics. In this paper, we demonstrate theoretically that, alike in classical systems, congestion plays a key role in the occurrence of a Braess paradox in mesoscopic networks.
Publisher: American Physical Society (APS)
Date: 16-03-2016
Publisher: Springer Science and Business Media LLC
Date: 13-03-2019
DOI: 10.1038/S41467-019-09194-X
Abstract: Scalable quantum processors require tunable two-qubit gates that are fast, coherent and long-range. The Heisenberg exchange interaction offers fast and coherent couplings for spin qubits, but is intrinsically short-ranged. Here, we demonstrate that its range can be increased by employing a multielectron quantum dot as a mediator, while preserving speed and coherence of the resulting spin-spin coupling. We do this by placing a large quantum dot with 50–100 electrons between a pair of two-electron double quantum dots that can be operated and measured simultaneously. Two-spin correlations identify coherent spin-exchange processes across the multielectron quantum dot. We further show that different physical regimes of the mediated exchange interaction allow a reduced susceptibility to charge noise at sweet spots, as well as positive and negative coupling strengths up to several gigahertz. These properties make multielectron dots attractive as scalable, voltage-controlled coherent coupling elements.
Publisher: American Physical Society (APS)
Date: 07-2003
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Frederico Martins.