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Moreau N, Brun B, Somanchi S, Watanabe K, Taniguchi T, Stampfer C, Hackens B. Upstream modes and antidots poison graphene quantum Hall effect. Nat Commun 2021; 12:4265. [PMID: 34253725 PMCID: PMC8275581 DOI: 10.1038/s41467-021-24481-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 06/17/2021] [Indexed: 11/09/2022] Open
Abstract
The quantum Hall effect is the seminal example of topological protection, as charge carriers are transmitted through one-dimensional edge channels where backscattering is prohibited. Graphene has made its marks as an exceptional platform to reveal new facets of this remarkable property. However, in conventional Hall bar geometries, topological protection of graphene edge channels is found regrettably less robust than in high mobility semi-conductors. Here, we explore graphene quantum Hall regime at the local scale, using a scanning gate microscope. We reveal the detrimental influence of antidots along the graphene edges, mediating backscattering towards upstream edge channels, hence triggering topological breakdown. Combined with simulations, our experimental results provide further insights into graphene quantum Hall channels vulnerability. In turn, this may ease future developments towards precise manipulation of topologically protected edge channels hosted in various types of two-dimensional crystals.
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Affiliation(s)
- N Moreau
- IMCN/NAPS, Université catholique de Louvain (UCLouvain), Louvain-la-Neuve, Belgium
| | - B Brun
- IMCN/NAPS, Université catholique de Louvain (UCLouvain), Louvain-la-Neuve, Belgium
| | - S Somanchi
- JARA-FIT and 2nd Institute of Physics-RWTH Aachen, Aachen, Germany
| | - K Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - C Stampfer
- JARA-FIT and 2nd Institute of Physics-RWTH Aachen, Aachen, Germany
| | - B Hackens
- IMCN/NAPS, Université catholique de Louvain (UCLouvain), Louvain-la-Neuve, Belgium.
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2
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Schwenk J, Kim S, Berwanger J, Ghahari F, Walkup D, Slot MR, Le ST, Cullen WG, Blankenship SR, Vranjkovic S, Hug HJ, Kuk Y, Giessibl FJ, Stroscio JA. Achieving μeV tunneling resolution in an in-operando scanning tunneling microscopy, atomic force microscopy, and magnetotransport system for quantum materials research. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:071101. [PMID: 32752869 PMCID: PMC7678032 DOI: 10.1063/5.0005320] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 06/04/2020] [Indexed: 06/11/2023]
Abstract
Research in new quantum materials requires multi-mode measurements spanning length scales, correlations of atomic-scale variables with a macroscopic function, and spectroscopic energy resolution obtainable only at millikelvin temperatures, typically in a dilution refrigerator. In this article, we describe a multi-mode instrument achieving a μeV tunneling resolution with in-operando measurement capabilities of scanning tunneling microscopy, atomic force microscopy, and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design and sample and tip transport systems, along with wiring, radio-frequency filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulator-superconductor tunnel junctions, with Josephson tunneling as a noise metering detector. After extensive testing and optimization, we have achieved less than 8 μeV instrument resolving capability for tunneling spectroscopy, which is 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.
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Affiliation(s)
- Johannes Schwenk
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Sungmin Kim
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Julian Berwanger
- Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany
| | - Fereshte Ghahari
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Daniel Walkup
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
| | - Marlou R. Slot
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Department of Physics, Georgetown University, Washington, DC 20007, USA
| | - Son T. Le
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Theiss Research, La Jolla, CA 92037, USA
| | - William G. Cullen
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Steven R. Blankenship
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Sasa Vranjkovic
- Institute of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Hans J. Hug
- Institute of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Young Kuk
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
| | - Franz J. Giessibl
- Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany
| | - Joseph A. Stroscio
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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3
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On the origins of transport inefficiencies in mesoscopic networks. Sci Rep 2018; 8:3017. [PMID: 29445196 PMCID: PMC5812991 DOI: 10.1038/s41598-018-21250-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 02/01/2018] [Indexed: 11/13/2022] Open
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.
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4
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Cabosart D, Felten A, Reckinger N, Iordanescu A, Toussaint S, Faniel S, Hackens B. Recurrent Quantum Scars in a Mesoscopic Graphene Ring. NANO LETTERS 2017; 17:1344-1349. [PMID: 28166405 DOI: 10.1021/acs.nanolett.6b03725] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
When coherent charge carriers cross micron-scale cavities, their dynamics can be governed by a few resonant states, also called "quantum scars", determined by the cavity geometry. Quantum scars can be described using theoretical tools but have also been directly imaged in the case of high-quality semiconductor cavities as well as in disordered graphene devices, thanks to scanning gate microscopy (SGM). Here, we discuss spatially resolved SGM images of low-temperature charge transport through a mesoscopic ring fabricated from high-quality monolayer graphene lying on top of hexagonal boron nitride. SGM images are decorated with a pattern of radial scars in the ring area, which is found to evolve smoothly and reappear when varying the charge-carrier energy. The energies separating recurrent patterns are found to be directly related to geometric dimensions of the ring. Moreover, a recurrence is also observed in simulations of the local density of states of a model graphene quantum ring. The observed recurrences are discussed in the light of recent predictions of relativistic quantum scars in mesoscopic graphene cavities.
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Affiliation(s)
- Damien Cabosart
- Nanoscopic Physics (NAPS), Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin du Cyclotron 2 bte L7.01.07, B-1348 Louvain-la-Neuve, Belgium
| | - Alexandre Felten
- Research Centre in Physics of Matter and Radiation (PMR), University of Namur (UNamur) , 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Nicolas Reckinger
- Research Centre in Physics of Matter and Radiation (PMR), University of Namur (UNamur) , 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Andra Iordanescu
- Nanoscopic Physics (NAPS), Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin du Cyclotron 2 bte L7.01.07, B-1348 Louvain-la-Neuve, Belgium
| | - Sébastien Toussaint
- Nanoscopic Physics (NAPS), Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin du Cyclotron 2 bte L7.01.07, B-1348 Louvain-la-Neuve, Belgium
| | - Sébastien Faniel
- Institute of Information and Communication Technologies, Electronics and Applied Mathematics/WINFAB, Université catholique de Louvain (UCL) , Place du Levant 3 bte L5.03.04, B-1348 Louvain-la-Neuve, Belgium
| | - Benoît Hackens
- Nanoscopic Physics (NAPS), Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain (UCL) , Chemin du Cyclotron 2 bte L7.01.07, B-1348 Louvain-la-Neuve, Belgium
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5
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Observation of interaction-induced modulations of a quantum Hall liquid's area. Nat Commun 2016; 7:12184. [PMID: 27396234 PMCID: PMC4942580 DOI: 10.1038/ncomms12184] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 06/08/2016] [Indexed: 11/30/2022] Open
Abstract
Studies of electronic interferometers, based on edge-channel transport in the quantum Hall effect regime, have been stimulated by the search for evidence of abelian and non-abelian anyonic statistics of fractional charges. In particular, the electronic Fabry–Pérot interferometer has been found to be Coulomb dominated, thus masking coherent Aharonov–Bohm interference patterns: the flux trapped within the interferometer remains unchanged as the applied magnetic field is varied, barring unobservable modulations of the interference area. Here we report on conductance measurements indicative of the interferometer's area ‘breathing' with the variation of the magnetic field, associated with observable (a fraction of a flux quantum) variations of the trapped flux. This is the result of partial (controlled) screening of Coulomb interactions. Our results introduce a novel experimental tool for probing anyonic statistics. Quantum Hall liquids play host to a wide range of unusual physics. Here, the authors use an electronic Fabry-Pérot interferometer to observe modulations of a quantum Hall liquid's area, which can offer a means to study the statistics of fractional charges.
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6
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Brun B, Martins F, Faniel S, Hackens B, Cavanna A, Ulysse C, Ouerghi A, Gennser U, Mailly D, Simon P, Huant S, Bayot V, Sanquer M, Sellier H. Electron Phase Shift at the Zero-Bias Anomaly of Quantum Point Contacts. PHYSICAL REVIEW LETTERS 2016; 116:136801. [PMID: 27081995 DOI: 10.1103/physrevlett.116.136801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Indexed: 06/05/2023]
Abstract
The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts.
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Affiliation(s)
- B Brun
- Université Grenoble Alpes, F-38000 Grenoble, France
- CNRS, Institut NEEL, F-38042 Grenoble, France
| | - F Martins
- IMCN/NAPS, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
| | - S Faniel
- IMCN/NAPS, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
| | - B Hackens
- IMCN/NAPS, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
| | - A Cavanna
- CNRS, Laboratoire de Photonique et de Nanostructures, UPR20, F-91460 Marcoussis, France
| | - C Ulysse
- CNRS, Laboratoire de Photonique et de Nanostructures, UPR20, F-91460 Marcoussis, France
| | - A Ouerghi
- CNRS, Laboratoire de Photonique et de Nanostructures, UPR20, F-91460 Marcoussis, France
| | - U Gennser
- CNRS, Laboratoire de Photonique et de Nanostructures, UPR20, F-91460 Marcoussis, France
| | - D Mailly
- CNRS, Laboratoire de Photonique et de Nanostructures, UPR20, F-91460 Marcoussis, France
| | - P Simon
- Laboratoire de Physique des Solides, Université Paris-Sud, F-91405 Orsay, France
| | - S Huant
- Université Grenoble Alpes, F-38000 Grenoble, France
- CNRS, Institut NEEL, F-38042 Grenoble, France
| | - V Bayot
- Université Grenoble Alpes, F-38000 Grenoble, France
- IMCN/NAPS, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
| | - M Sanquer
- Université Grenoble Alpes, F-38000 Grenoble, France
- CEA, INAC-SPSMS, F-38054 Grenoble, France
| | - H Sellier
- Université Grenoble Alpes, F-38000 Grenoble, France
- CNRS, Institut NEEL, F-38042 Grenoble, France
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7
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Beukman AJA, Qu F, West KW, Pfeiffer LN, Kouwenhoven LP. A Noninvasive Method for Nanoscale Electrostatic Gating of Pristine Materials. NANO LETTERS 2015; 15:6883-6888. [PMID: 26375825 DOI: 10.1021/acs.nanolett.5b02800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Electrostatic gating is essential for defining and control of semiconducting devices. However, nanofabrication processes required for depositing gates inevitably degrade the pristine quality of the material of interest. Examples of materials that suffer from such degradation include ultrahigh mobility GaAs/AlGaAs two-dimensional electron gases (2DEGs), graphene, topological insulators, and nanowires. To preserve the pristine material properties, we have developed a flip-chip setup where gates are separated from the material by a vacuum, which allows nanoscale electrostatic gating of the material without exposing it to invasive nanoprocessing. An additional benefit is the vacuum between gates and material, which, unlike gate dielectrics, is free from charge traps. We demonstrate the operation and feasibility of the flip-chip setup by achieving quantum interference at integer quantum Hall states in a Fabry-Pérot interferometer based on a GaAs/AlGaAs 2DEG. Our results pave the way for the study of exotic phenomena including fragile fractional quantum Hall states by preserving the high quality of the material.
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Affiliation(s)
- Arjan J A Beukman
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology , GA 2600 Delft, The Netherlands
| | - Fanming Qu
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology , GA 2600 Delft, The Netherlands
| | - Ken W West
- Department of Electrical Engineering, Princeton University , Princeton, New Jersey 08544, United States
| | - Loren N Pfeiffer
- Department of Electrical Engineering, Princeton University , Princeton, New Jersey 08544, United States
| | - Leo P Kouwenhoven
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology , GA 2600 Delft, The Netherlands
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8
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Gowda MJ, Bhojani U, Devadasan N, Beerenahally TS. The rising burden of chronic conditions among urban poor: a three-year follow-up survey in Bengaluru, India. BMC Health Serv Res 2015; 15:330. [PMID: 26275608 PMCID: PMC4537574 DOI: 10.1186/s12913-015-0999-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Accepted: 08/11/2015] [Indexed: 11/13/2022] Open
Abstract
Background Chronic conditions are on rise globally and in India. Prevailing intra-urban inequities in access to healthcare services compounds the problems faced by urban poor. This paper reports the trends in self-reported prevalence of chronic conditions and health-seeking pattern among residents of a poor urban neighborhood in south India. Methods A cross sectional survey of 1099 households (5340 individuals) was conducted using a structured questionnaire. The prevalence and health-seeking pattern for chronic conditions in general and for hypertension and diabetes in particular were assessed and compared with a survey conducted in the same community three years ago. The predictors of prevalence and health-seeking pattern were analyzed through a multivariable logistic regression analysis. Results The overall self-reported prevalence of chronic conditions was 12 %, with hypertension (7 %) and diabetes (5.8 %) being the common conditions. The self-reported prevalence of chronic conditions increased by 3.8 percentage point over a period of three years (OR: 1.5). Older people, women and people living below the poverty line had greater odds of having chronic conditions across the two studies compared. Majority of patients (89.3 %) sought care from private health facilities indicating a decrease by 8.7 percentage points in use of government health facility compared to the earlier study (OR: 0.5). Patients seeking care from super specialty hospitals and those living below the poverty line were more likely to seek care from government health facilities. Conclusion There is need to strengthen health services with a preferential focus on government services to assure affordable care for chronic conditions to urban poor.
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Affiliation(s)
- Mrunalini J Gowda
- Institute of Public Health, 250, 2nd C Main, Girinagar 1st Phase, Bengaluru, 560085, India.
| | - Upendra Bhojani
- Institute of Public Health, 250, 2nd C Main, Girinagar 1st Phase, Bengaluru, 560085, India. .,Department of Public Health, Ghent University, De Pintelaan 185 4K3 9000, Ghent, Belgium.
| | - Narayanan Devadasan
- Institute of Public Health, 250, 2nd C Main, Girinagar 1st Phase, Bengaluru, 560085, India.
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9
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Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy. Nat Commun 2014; 5:4290. [DOI: 10.1038/ncomms5290] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 06/04/2014] [Indexed: 11/09/2022] Open
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10
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Aoki N, da Cunha CR, Akis R, Ferry DK, Ochiai Y. Scanning gate imaging of a disordered quantum point contact. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:193202. [PMID: 24763258 DOI: 10.1088/0953-8984/26/19/193202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Scanning gate microscopy (SGM) is a novel technique that has been used to image characteristic features related to the coherent electron flow in mesoscopic structures. For instance, SGM has successfully been applied to study peculiar electron transport properties that arise due to small levels of disorder in a system. The particular case of an InGaAs quantum well layer in a heterostructure, which is dominated by a quasi-ballistic regime, was analyzed. A quantum point contact fabricated onto this material exhibits conduction fluctuations that are not expected in typical high-mobility heterostructures such as AlGaAs/GaAs. SGM revealed not only interference patterns corresponding to specific conductance fluctuations but also mode-dependent resistance peaks corresponding to the first and second quantum levels of conductance (2e(2)/h) at zero magnetic field. On the other hand, clear conductance plateaus originating from the integer quantum Hall effect were observed at high magnetic fields. The physical size of incompressible edge channels was estimated from cross-sectional analysis of these images.
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Affiliation(s)
- N Aoki
- Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
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11
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Daniel OJ, Adejumo OA, Adejumo EN, Owolabi RS, Braimoh RW. Prevalence of hypertension among urban slum dwellers in Lagos, Nigeria. J Urban Health 2013; 90:1016-25. [PMID: 23440487 PMCID: PMC3853173 DOI: 10.1007/s11524-013-9795-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Urban slum dwellers are not only prone to develop communicable diseases but also to non-communicable disease (NCDs). The extent and magnitude of NCDs among slum dwellers is largely unknown in Nigeria. A total of 964 adults aged 20-81 years (male 330 and female 634) residing in the urban slum of Ajegunle in Lagos State, Nigeria were studied to determine the prevalence of hypertension and associated factors. The overall prevalence of hypertension was 38.2 %. Of the 368 respondents identified as having hypertension, only 50 (5.2 %) respondents were previously aware of their diagnosis. Of the 50 known hypertensive patients, 48(96 %) had poor control of their high blood pressure. The socio-demographic factors significantly associated with hypertension status were age, sex, education, religion, BMI, and marital status. The study concludes a high prevalence of hypertension among urban slums dwellers in Lagos. The need for government to develop policies for the control of hypertension, improve access to early diagnosis and provide an enabling socioeconomic environment while promoting healthy living.
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Affiliation(s)
- Olusoji James Daniel
- Department of Community Medicine and Primary Care, Olabisi Onabanjo University Teaching Hospital, Sagamu, Ogun State, Nigeria,
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12
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Coherent tunnelling across a quantum point contact in the quantum Hall regime. Sci Rep 2013; 3:1416. [PMID: 23475303 PMCID: PMC3593222 DOI: 10.1038/srep01416] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 02/22/2013] [Indexed: 12/03/2022] Open
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.
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13
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Pelliccione M, Sciambi A, Bartel J, Keller AJ, Goldhaber-Gordon D. Design of a scanning gate microscope for mesoscopic electron systems in a cryogen-free dilution refrigerator. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:033703. [PMID: 23556823 DOI: 10.1063/1.4794767] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We report on our design of a scanning gate microscope housed in a cryogen-free dilution refrigerator with a base temperature of 15 mK. The recent increase in efficiency of pulse tube cryocoolers has made cryogen-free systems popular in recent years. However, this new style of cryostat presents challenges for performing scanning probe measurements, mainly as a result of the vibrations introduced by the cryocooler. We demonstrate scanning with root-mean-square vibrations of 0.8 nm at 3 K and 2.1 nm at 15 mK in a 1 kHz bandwidth with our design. Using Coulomb blockade thermometry on a GaAs/AlGaAs gate-defined quantum dot, we demonstrate an electron temperature of 45 mK.
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Affiliation(s)
- M Pelliccione
- Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA
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14
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Can T, Morr DK. Atomic resolution imaging of currents in nanoscopic quantum networks via scanning tunneling microscopy. PHYSICAL REVIEW LETTERS 2013; 110:086802. [PMID: 23473184 DOI: 10.1103/physrevlett.110.086802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Indexed: 06/01/2023]
Abstract
We propose a new method for atomic-scale imaging of spatial current patterns in nanoscopic quantum networks by using scanning tunneling microscopy (STM). By measuring the current flowing from the STM tip into one of the leads attached to the network as a function of tip position, one obtains an atomically resolved spatial image of "current riverbeds" whose spatial structure reflects the coherent flow of electrons out of equilibrium. We show that this method can be successfully applied in a variety of network topologies and is robust against dephasing effects.
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Affiliation(s)
- Tankut Can
- Department of Physics and James Franck Institute, University of Chicago, Chicago, Illinois 60637, USA
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15
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Connolly MR, Puddy RK, Logoteta D, Marconcini P, Roy M, Griffiths JP, Jones GAC, Maksym PA, Macucci M, Smith CG. Unraveling quantum Hall breakdown in bilayer graphene with scanning gate microscopy. NANO LETTERS 2012; 12:5448-5454. [PMID: 23078572 DOI: 10.1021/nl3015395] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Investigating the structure of quantized plateaus in the Hall conductance of graphene is a powerful way of probing its crystalline and electronic structure and will also help to establish whether graphene can be used as a robust standard of resistance for quantum metrology. We use low-temperature scanning gate microscopy to image the interplateau breakdown of the quantum Hall effect in an exfoliated bilayer graphene flake. Scanning gate images captured during breakdown exhibit intricate patterns where the conductance is strongly affected by the presence of the scanning probe tip. The maximum density and intensity of the tip-induced conductance perturbations occur at half-integer filling factors, midway between consecutive quantum Hall plateau, while the intensity of individual sites shows a strong dependence on tip-voltage. Our results are well-described by a model based on quantum percolation which relates the points of high responsivity to tip-induced scattering in a network of saddle points separating localized states.
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Affiliation(s)
- M R Connolly
- Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, United Kingdom.
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Pala M, Sellier H, Hackens B, Martins F, Bayot V, Huant S. A new transport phenomenon in nanostructures: a mesoscopic analog of the Braess paradox encountered in road networks. NANOSCALE RESEARCH LETTERS 2012; 7:472. [PMID: 22913510 PMCID: PMC3492112 DOI: 10.1186/1556-276x-7-472] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Accepted: 08/02/2012] [Indexed: 06/01/2023]
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.
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Affiliation(s)
- Marco Pala
- IMEP-LAHC, Grenoble INP, Minatec, BP 257, Grenoble, F-38016, France
| | - Hermann Sellier
- Institut Néel, CNRS and Université Joseph Fourier, BP 166, Grenoble, F-38042, France
| | - Benoit Hackens
- IMCN/NAPS, UCLouvain, 2 Chemin du Cyclotron, Louvain-la-Neuve, B-1348, Belgium
| | - Frederico Martins
- IMCN/NAPS, UCLouvain, 2 Chemin du Cyclotron, Louvain-la-Neuve, B-1348, Belgium
| | - Vincent Bayot
- Institut Néel, CNRS and Université Joseph Fourier, BP 166, Grenoble, F-38042, France
- IMCN/NAPS, UCLouvain, 2 Chemin du Cyclotron, Louvain-la-Neuve, B-1348, Belgium
| | - Serge Huant
- Institut Néel, CNRS and Université Joseph Fourier, BP 166, Grenoble, F-38042, France
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McClure DT, Chang W, Marcus CM, Pfeiffer LN, West KW. Fabry-Perot interferometry with fractional charges. PHYSICAL REVIEW LETTERS 2012; 108:256804. [PMID: 23004633 DOI: 10.1103/physrevlett.108.256804] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Indexed: 06/01/2023]
Abstract
Resistance oscillations in electronic Fabry-Perot interferometers near fractional quantum Hall (FQH) filling factors 1/3, 2/3, 4/3, and 5/3 in the constrictions are compared to those near integer quantum Hall (IQH) filling factors in the same devices and at the same gate voltages. Two-dimensional plots of resistance versus gate voltage and magnetic field indicate that all oscillations are Coulomb dominated. A charging-model analysis of gate-voltage periods yields an effective tunneling charge e* ≈ e/3 for all FQH states and e* ≈ e for IQH states. Temperature decay of the oscillations appears exponential, qualitatively consistent with a recent prediction, and the surprising filling-factor dependence of the associated energy scale may shed light on edge structure.
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Affiliation(s)
- D T McClure
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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Pala MG, Baltazar S, Liu P, Sellier H, Hackens B, Martins F, Bayot V, Wallart X, Desplanque L, Huant S. Transport inefficiency in branched-out mesoscopic networks: an analog of the Braess paradox. PHYSICAL REVIEW LETTERS 2012; 108:076802. [PMID: 22401236 DOI: 10.1103/physrevlett.108.076802] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Indexed: 05/31/2023]
Abstract
We present evidence for a counterintuitive behavior of semiconductor mesoscopic networks that is the analog of the Braess paradox encountered in classical networks. A numerical simulation of quantum transport in a two-branch mesoscopic network reveals that adding a third branch can paradoxically induce transport inefficiency that manifests itself in a sizable conductance drop of the network. A scanning-probe experiment using a biased tip to modulate the transmission of one branch in the network reveals the occurrence of this paradox by mapping the conductance variation as a function of the tip voltage and position.
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Affiliation(s)
- M G Pala
- IMEP-LAHC, Grenoble INP, Minatec, BP 257, Grenoble, France.
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