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A Review on Graphene-Based Nano-Electromechanical Resonators: Fabrication, Performance, and Applications. MICROMACHINES 2022; 13:mi13020215. [PMID: 35208343 PMCID: PMC8880531 DOI: 10.3390/mi13020215] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 01/24/2022] [Accepted: 01/24/2022] [Indexed: 11/16/2022]
Abstract
The emergence of graphene and other two-dimensional materials overcomes the limitation in the characteristic size of silicon-based micro-resonators and paved the way in the realization of nano-mechanical resonators. In this paper, we review the progress to date of the research on the fabrication methods, resonant performance, and device applications of graphene-based nano-mechanical resonators, from theoretical simulation to experimental results, and summarize both the excitation and detection schemes of graphene resonators. In recent years, the applications of graphene resonators such as mass sensors, pressure sensors, and accelerometers gradually moved from theory to experiment, which are specially introduced in this review. To date, the resonance performance of graphene-based nano-mechanical resonators is widely studied by theoretical approaches, while the corresponding experiments are still in the preliminary stage. However, with the continuous progress of the device fabrication and detection technique, and with the improvement of the theoretical model, suspended graphene membranes will widen the potential for ultralow-loss and high-sensitivity mechanical resonators in the near future.
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Alaloul M, Khurgin JB. Electrical control of all-optical graphene switches. OPTICS EXPRESS 2022; 30:1950-1966. [PMID: 35209346 DOI: 10.1364/oe.441710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 10/14/2021] [Indexed: 06/14/2023]
Abstract
Graphene has emerged as an ultrafast photonic material for on-chip all-optical switching applications. However, its atomic thickness limits its interaction with guided optical modes, resulting in a high switching energy per bit. Herein, we propose a novel technique to electrically control the switching energy of an all-optical graphene switch on a silicon nitride waveguide. Using this technique, we theoretically demonstrate a 120 µm long all-optical graphene switch with an 8.9 dB extinction ratio, 2.4 dB insertion loss, a switching time of <100 fs, a fall time of <5 ps, and a 235 fJ switching energy at 2.5 V bias, where the applied voltage reduces the switching energy by ∼16×. This technique paves the way for the emergence of ultra-efficient all-optical graphene switches that will meet the energy demands of next-generation photonic computing systems, and it is a promising alternative to lossy plasmon-enhanced devices.
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Mikheev E, Rosen IT, Goldhaber-Gordon D. Quantized critical supercurrent in SrTiO 3-based quantum point contacts. SCIENCE ADVANCES 2021; 7:eabi6520. [PMID: 34597141 PMCID: PMC10938545 DOI: 10.1126/sciadv.abi6520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 08/11/2021] [Indexed: 06/13/2023]
Abstract
Superconductivity in SrTiO3 occurs at remarkably low carrier densities and therefore, unlike conventional superconductors, can be controlled by electrostatic gates. Here, we demonstrate nanoscale weak links connecting superconducting leads, all within a single material, SrTiO3. Ionic liquid gating accumulates carriers in the leads, and local electrostatic gates are tuned to open the weak link. These devices behave as superconducting quantum point contacts with a quantized critical supercurrent. This is a milestone toward establishing SrTiO3 as a single-material platform for mesoscopic superconducting transport experiments that also intrinsically contains the necessary ingredients to engineer topological superconductivity.
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Affiliation(s)
- Evgeny Mikheev
- Department of Physics, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Ilan T. Rosen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
| | - David Goldhaber-Gordon
- Department of Physics, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
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4
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Bhandari S, Lee GH, Watanabe K, Taniguchi T, Kim P, Westervelt RM. Imaging Andreev Reflection in Graphene. NANO LETTERS 2020; 20:4890-4894. [PMID: 32484357 DOI: 10.1021/acs.nanolett.0c00903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Coherent charge transport along ballistic paths can be introduced into graphene by Andreev reflection, for which an electron reflects from a superconducting contact as a hole, while a Cooper pair is transmitted. We use liquid-helium cooled scanning gate microscopy (SGM) to image Andreev reflection in graphene in the magnetic focusing regime, where carriers move along cyclotron orbits between contacts. Images of flow are obtained by deflecting carrier paths and displaying the resulting change in conductance. When electrons enter the superconductor, Andreev-reflected holes leave for the collecting contact. To test the results, we destroy Andreev reflection with a large current and by heating above the critical temperature. In both cases, the reflected carriers change from holes to electrons.
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Affiliation(s)
- Sagar Bhandari
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- Department of Physics and Engineering, Slippery Rock University, Slippery Rock, Pennsylvania 16057, United States
| | - Gil-Ho Lee
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Philip Kim
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Robert M Westervelt
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
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Liu Y, Abhilash TS, Laitinen A, Tan Z, Liu GJ, Hakonen P. Dry transfer method for suspended graphene on lift-off-resist: simple ballistic devices with Fabry-Pérot interference. NANOTECHNOLOGY 2019; 30:25LT01. [PMID: 30840930 DOI: 10.1088/1361-6528/ab0d30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We demonstrate a fabrication scheme for clean suspended structures using chemical-vapor-deposition-grown graphene and a dry transfer method on lift-off-resist-coated substrates to facilitate suspended graphene nanoelectronic devices for technological applications. It encompasses the demands for scalable fabrication as well as for ultra-fast response due to weak coupling to environment. The fabricated devices exhibited initially a weak field-effect response with substantial positive (p) doping which transformed into weak negative (n) doping upon current annealing at the temperature of 4 K. With increased annealing current, n-doping gradually decreased while the Dirac peak position approached zero in gate voltage. An ultra-low residual charge density of 9 × 108 cm-2 and a mobility of 1.9 × 105 cm2 V-1 s-1 were observed. Our samples display clear Fabry-Pérot (FP) conductance oscillation which indicates ballistic electron transport. The spacings of the FP oscillations are found to depend on the charge density in a manner that agrees with theoretical modeling based on Klein tunneling of Dirac particles. The ultra-low residual charge, the FP oscillations with density dependent period, and the high mobility prove the excellent quality of our suspended graphene devices. Owing to its simplicity, scalability and robustness, this fabrication scheme enhances possibilities for production of suspended, high-quality, two-dimensional-material structures for novel electronic applications.
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Affiliation(s)
- Ying Liu
- Science and Technology on Integrated Logistics Support Laboratory, National University of Defense Technology, Changsha, 410073, People's Republic of China. Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, FI-02150, Finland
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6
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Ridderbos J, Brauns M, Shen J, de Vries FK, Li A, Bakkers EPAM, Brinkman A, Zwanenburg FA. Josephson Effect in a Few-Hole Quantum Dot. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802257. [PMID: 30260519 DOI: 10.1002/adma.201802257] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 07/11/2018] [Indexed: 06/08/2023]
Abstract
A Ge-Si core-shell nanowire is used to realize a Josephson field-effect transistor with highly transparent contacts to superconducting leads. By changing the electric field, access to two distinct regimes, not combined before in a single device, is gained: in the accumulation mode the device is highly transparent and the supercurrent is carried by multiple subbands, while near depletion, the supercurrent is carried by single-particle levels of a strongly coupled quantum dot operating in the few-hole regime. These results establish Ge-Si nanowires as an important platform for hybrid superconductor-semiconductor physics and Majorana fermions.
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Affiliation(s)
- Joost Ridderbos
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
| | - Matthias Brauns
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
| | - Jie Shen
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, Delft, The Netherlands
| | - Folkert K de Vries
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, Delft, The Netherlands
| | - Ang Li
- Department of Applied Physics, Eindhoven University of Technology, Postbox 513, 5600 MB, Eindhoven, The Netherlands
| | - Erik P A M Bakkers
- QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, Delft, The Netherlands
- Department of Applied Physics, Eindhoven University of Technology, Postbox 513, 5600 MB, Eindhoven, The Netherlands
| | - Alexander Brinkman
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
| | - Floris A Zwanenburg
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
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7
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Macedo LJA, Iost RM, Hassan A, Balasubramanian K, Crespilho FN. Bioelectronics and Interfaces Using Monolayer Graphene. ChemElectroChem 2018. [DOI: 10.1002/celc.201800934] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Lucyano J. A. Macedo
- São Carlos Institute of Chemistry; University of São Paulo; São Carlos SP 13560-970 Brazil
| | - Rodrigo M. Iost
- Department of Chemistry School of Analytical Sciences Adlershof (SALSA) and IRIS Adlershof; Humboldt-Universität zu Berlin; Berlin 10099 Germany
| | - Ayaz Hassan
- São Carlos Institute of Chemistry; University of São Paulo; São Carlos SP 13560-970 Brazil
| | - Kannan Balasubramanian
- Department of Chemistry School of Analytical Sciences Adlershof (SALSA) and IRIS Adlershof; Humboldt-Universität zu Berlin; Berlin 10099 Germany
| | - Frank N. Crespilho
- São Carlos Institute of Chemistry; University of São Paulo; São Carlos SP 13560-970 Brazil
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8
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Lee GH, Lee HJ. Proximity coupling in superconductor-graphene heterostructures. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:056502. [PMID: 29451135 DOI: 10.1088/1361-6633/aaafe1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable 2D platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given.
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Affiliation(s)
- Gil-Ho Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea. Department of Physics, Harvard University, Cambridge, MA 02138, United States of America
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Tailoring supercurrent confinement in graphene bilayer weak links. Nat Commun 2018; 9:1722. [PMID: 29712916 PMCID: PMC5928064 DOI: 10.1038/s41467-018-04153-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Accepted: 04/11/2018] [Indexed: 11/08/2022] Open
Abstract
The Josephson effect is one of the most studied macroscopic quantum phenomena in condensed matter physics and has been an essential part of the quantum technologies development over the last decades. It is already used in many applications such as magnetometry, metrology, quantum computing, detectors or electronic refrigeration. However, developing devices in which the induced superconductivity can be monitored, both spatially and in its magnitude, remains a serious challenge. In this work, we have used local gates to control confinement, amplitude and density profile of the supercurrent induced in one-dimensional nanoscale constrictions, defined in bilayer graphene-hexagonal boron nitride van der Waals heterostructures. The combination of resistance gate maps, out-of-equilibrium transport, magnetic interferometry measurements, analytical and numerical modelling enables us to explore highly tunable superconducting weak links. Our study opens the path way to design more complex superconducting circuits based on this principle, such as electronic interferometers or transition-edge sensors.
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10
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Zhu M, Ben Shalom M, Mishchsenko A, Fal'ko V, Novoselov K, Geim A. Supercurrent and multiple Andreev reflections in micrometer-long ballistic graphene Josephson junctions. NANOSCALE 2018; 10:3020-3025. [PMID: 29372736 DOI: 10.1039/c7nr05904c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Ballistic Josephson junctions are predicted to support a number of exotic physics processess, providing an ideal system to inject the supercurrent in the quantum Hall regime. Herein, we demonstrate electrical transport measurements on ballistic superconductor-graphene-superconductor junctions by contacting graphene to niobium with a junction length up to 1.5 μm. Hexagonal boron nitride encapsulation and one-dimensional edge contacts guarantee high-quality graphene Josephson junctions with a mean free path of several micrometers and record-low contact resistance. Transports in normal states including the observation of Fabry-Pérot oscillations and Sharvin resistance conclusively witness the ballistic propagation in the junctions. The critical current density JC is over one order of magnitude larger than that of the previously reported junctions. Away from the charge neutrality point, the ICRN product (IC is the critical current and RN the normal state resistance of junction) is nearly a constant, independent of carrier density n, which agrees well with the theory for ballistic Josephson junctions. Multiple Andreev reflections up to the third order are observed for the first time by measuring the differential resistance in the micrometer-long ballistic graphene Josephson junctions.
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Affiliation(s)
- Mengjian Zhu
- School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK.
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11
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Zulkefli MA, Mohamed MA, Siow KS, Yeop Majlis B, Kulothungan J, Muruganathan M, Mizuta H. Three-Dimensional Finite Element Method Simulation of Perforated Graphene Nano-Electro-Mechanical (NEM) Switches. MICROMACHINES 2017; 8:E236. [PMID: 30400428 PMCID: PMC6190186 DOI: 10.3390/mi8080236] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 07/24/2017] [Accepted: 07/25/2017] [Indexed: 11/30/2022]
Abstract
The miniaturization trend leads to the development of a graphene based nanoelectromechanical (NEM) switch to fulfill the high demand in low power device applications. In this article, we highlight the finite element (FEM) simulation of the graphene-based NEM switches of fixed-fixed ends design with beam structures which are perforated and intact. Pull-in and pull-out characteristics are analyzed by using the FEM approach provided by IntelliSuite software, version 8.8.5.1. The FEM results are consistent with the published experimental data. This analysis shows the possibility of achieving a low pull-in voltage that is below 2 V for a ratio below 15:0.03:0.7 value for the graphene beam length, thickness, and air gap thickness, respectively. The introduction of perforation in the graphene beam-based NEM switch further achieved the pull-in voltage as low as 1.5 V for a 250 nm hole length, 100 nm distance between each hole, and 12-number of hole column. Then, a von Mises stress analysis is conducted to investigate the mechanical stability of the intact and perforated graphene-based NEM switch. This analysis shows that a longer and thinner graphene beam reduced the von Mises stress. The introduction of perforation concept further reduced the von Mises stress at the graphene beam end and the beam center by approximately ~20⁻35% and ~10⁻20%, respectively. These theoretical results, performed by FEM simulation, are expected to expedite improvements in the working parameter and dimension for low voltage and better mechanical stability operation of graphene-based NEM switch device fabrication.
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Affiliation(s)
- Mohd Amir Zulkefli
- Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 UKM-Bangi, Selangor, Malaysia.
| | - Mohd Ambri Mohamed
- Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 UKM-Bangi, Selangor, Malaysia.
| | - Kim S Siow
- Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 UKM-Bangi, Selangor, Malaysia.
| | - Burhanuddin Yeop Majlis
- Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 UKM-Bangi, Selangor, Malaysia.
| | - Jothiramalingam Kulothungan
- School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292, Japan.
| | - Manoharan Muruganathan
- School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292, Japan.
| | - Hiroshi Mizuta
- School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292, Japan.
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12
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Legrand D, Le Cunff LO, Bruyant A, Salas-Montiel R, Liu Z, Tay BK, Maurer T, Bachelot R. Surface plasmons in suspended graphene: launching with in-plane gold nanoantenna and propagation properties. OPTICS EXPRESS 2017; 25:17306-17321. [PMID: 28789223 DOI: 10.1364/oe.25.017306] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Accepted: 06/15/2017] [Indexed: 06/07/2023]
Abstract
Graphene physics and plasmonics are two fields which, once combined, promise a variety of exciting applications. One of those applications is the integration of active nano-optoelectronic devices in electronic systems, using the fact that plasmons in graphene are tunable, highly confined and weakly damped. A crucial challenge remains before achieving these active devices: finding a platform enabling a high propagation of Graphene Plasmons Polaritons (GPPs). Suspended graphene presenting ultrahigh electron mobility has given rise to increasing interest. We numerically studied the plasmonic properties of suspended graphene. We propose a hybrid configuration and a set of conditions to launch graphene plasmons via an in-plane gold nanoantenna, for micrometric propagation of surface plasmons in suspended graphene. Finally, we propose a realistic optoelectronic device based on the use of suspended graphene.
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14
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Kubozono Y, Eguchi R, Goto H, Hamao S, Kambe T, Terao T, Nishiyama S, Zheng L, Miao X, Okamoto H. Recent progress on carbon-based superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:334001. [PMID: 27351938 DOI: 10.1088/0953-8984/28/33/334001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T c and interesting physical features.
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Affiliation(s)
- Yoshihiro Kubozono
- Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
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15
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Amet F, Ke CT, Borzenets IV, Wang J, Watanabe K, Taniguchi T, Deacon RS, Yamamoto M, Bomze Y, Tarucha S, Finkelstein G. Supercurrent in the quantum Hall regime. Science 2016; 352:966-9. [PMID: 27199424 DOI: 10.1126/science.aad6203] [Citation(s) in RCA: 142] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 04/12/2016] [Indexed: 11/02/2022]
Abstract
A promising route for creating topological states and excitations is to combine superconductivity and the quantum Hall (QH) effect. Despite this potential, signatures of superconductivity in the QH regime remain scarce, and a superconducting current through a QH weak link has been challenging to observe. We demonstrate the existence of a distinct supercurrent mechanism in encapsulated graphene samples contacted by superconducting electrodes, in magnetic fields as high as 2 tesla. The observation of a supercurrent in the QH regime marks an important step in the quest for exotic topological excitations, such as Majorana fermions and parafermions, which may find applications in fault-tolerant quantum computing.
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Affiliation(s)
- F Amet
- Department of Physics, Duke University, Durham, NC 27708, USA. Department of Physics and Astronomy, Appalachian State University, Boone, NC 28607, USA.
| | - C T Ke
- Department of Physics, Duke University, Durham, NC 27708, USA
| | - I V Borzenets
- Department of Applied Physics, University of Tokyo, Bunkyo-ku,Tokyo, 113-8656, Japan
| | - J Wang
- Department of Physics, Duke University, Durham, NC 27708, USA
| | - K Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - T Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - R S Deacon
- Center for Emergent Matter Science (CEMS), RIKEN, Wako-shi, Saitama 351-0198, Japan
| | - M Yamamoto
- Department of Applied Physics, University of Tokyo, Bunkyo-ku,Tokyo, 113-8656, Japan. PRESTO, Japan Science and Technology Agency, Kawaguchi-shi, Saitama 332-0012, Japan
| | - Y Bomze
- Department of Physics, Duke University, Durham, NC 27708, USA
| | - S Tarucha
- Department of Applied Physics, University of Tokyo, Bunkyo-ku,Tokyo, 113-8656, Japan. Center for Emergent Matter Science (CEMS), RIKEN, Wako-shi, Saitama 351-0198, Japan
| | - G Finkelstein
- Department of Physics, Duke University, Durham, NC 27708, USA.
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A proposed experimental diagnosing of specular Andreev reflection using the spin orbit interaction. Sci Rep 2016; 6:29279. [PMID: 27388426 PMCID: PMC4937350 DOI: 10.1038/srep29279] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/14/2016] [Indexed: 11/23/2022] Open
Abstract
Based on the Dirac-Bogoliubov-de Gennes equation, we theoretically investigate the chirality-resolved transport properties through a superconducting heterojunction in the presence of both the Rashba spin orbit interaction (RSOI) and the Dresselhaus spin orbit interaction (DSOI). Our results show that, if only the RSOI is present, the chirality-resolved Andreev tunneling conductance can be enhanced in the superconducting gap, while it always shows a suppression effect for the case of the DSOI alone. In contrast to the similar dependence of the specular Andreev zero bias tunneling conductance on the SOI, the retro-Andreev zero bias tunneling conductance exhibit the distinct dependence on the RSOI and the DSOI. Moreover, the zero-bias tunneling conductances for the retro-Andreev reflection (RAR) and the specular Andreev reflection (SAR) also show a qualitative difference with respect to the barrier parameters. When the RSOI and the DSOI are finite, three orders of magnitude enhancement of specular Andreev tunneling conductance is revealed. Furthermore, by analyzing the balanced SOI case, we find that the RAR is in favor of a parabolic dispersion, but a linear dispersion is highly desired for the SAR. These results shed light on the diagnosing of the SAR in graphene when subjected to both kinds of SOI.
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Kumaravadivel P, Du X. Signatures of evanescent transport in ballistic suspended graphene-superconductor junctions. Sci Rep 2016; 6:24274. [PMID: 27080733 PMCID: PMC4832184 DOI: 10.1038/srep24274] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 03/16/2016] [Indexed: 11/17/2022] Open
Abstract
In Dirac materials, the low energy excitations behave like ultra-relativistic massless particles with linear energy dispersion. A particularly intriguing phenomenon arises with the intrinsic charge transport behavior at the Dirac point where the charge density approaches zero. In graphene, a 2-D Dirac fermion gas system, it was predicted that charge transport near the Dirac point is carried by evanescent modes, resulting in unconventional “pseudo-diffusive” charge transport even in the absence of disorder. In the past decade, experimental observation of this phenomenon remained challenging due to the presence of strong disorder in graphene devices which limits the accessibility of the low carrier density regime close enough to the Dirac point. Here we report transport measurements on ballistic suspended graphene-Niobium Josephson weak links that demonstrate a transition from ballistic to pseudo-diffusive like evanescent transport below a carrier density of ~1010 cm−2. Approaching the Dirac point, the sub-harmonic gap structures due to multiple Andreev reflections display a strong Fermi energy-dependence and become increasingly pronounced, while the normalized excess current through the superconductor-graphene interface decreases sharply. Our observations are in qualitative agreement with the long standing theoretical prediction for the emergence of evanescent transport mediated pseudo-diffusive transport in graphene.
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Affiliation(s)
| | - Xu Du
- Department of Physics and Astronomy, Stony Brook University, New York, USA
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Bartolomeo AD, Giubileo F, Romeo F, Sabatino P, Carapella G, Iemmo L, Schroeder T, Lupina G. Graphene field effect transistors with niobium contacts and asymmetric transfer characteristics. NANOTECHNOLOGY 2015; 26:475202. [PMID: 26535591 DOI: 10.1088/0957-4484/26/47/475202] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
We fabricate back-gated field effect transistors using niobium electrodes on mechanically exfoliated monolayer graphene and perform electrical characterization in the pressure range from atmospheric down to 10(-4) mbar. We study the effect of room temperature vacuum degassing and report asymmetric transfer characteristics with a resistance plateau in the n-branch. We show that weakly chemisorbed Nb acts as p-dopant on graphene and explain the transistor characteristics by Nb/graphene interaction with unpinned Fermi level at the interface.
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Affiliation(s)
- Antonio Di Bartolomeo
- Dipartimento di Fisica 'E.R. Caianiello' and Centro Interdipartimentale NanoMates, Università degli Studi di Salerno, Fisciano, Salerno, Italy. CNR-SPIN, Fisciano, Salerno, Italy
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Ong FR, Cui Z, Yurtalan MA, Vojvodin C, Papaj M, Orgiazzi JLFX, Deng C, Bal M, Lupascu A. Suspended graphene devices with local gate control on an insulating substrate. NANOTECHNOLOGY 2015; 26:405201. [PMID: 26377034 DOI: 10.1088/0957-4484/26/40/405201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present a fabrication process for graphene-based devices where a graphene monolayer is suspended above a local metallic gate placed in a trench. As an example we detail the fabrication steps of a graphene field-effect transistor. The devices are built on a bare high-resistivity silicon substrate. At temperatures of 77 K and below, we observe the field-effect modulation of the graphene resistivity by a voltage applied to the gate. This fabrication approach enables new experiments involving graphene-based superconducting qubits and nano-electromechanical resonators. The method is applicable to other two-dimensional materials.
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Affiliation(s)
- Florian R Ong
- Institute for Quantum Computing, Department of Physics and Astronomy, and Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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Montemurro D, Stornaiuolo D, Massarotti D, Ercolani D, Sorba L, Beltram F, Tafuri F, Roddaro S. Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis. NANOTECHNOLOGY 2015; 26:385302. [PMID: 26335273 DOI: 10.1088/0957-4484/26/38/385302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis, which allows one to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of hybrid Josephson junctions based on semiconducting nanowires coupled with high-temperature superconductors is discussed.
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Affiliation(s)
- D Montemurro
- Seconda Università degli Studi di Napoli, Dipartimento di Ingegneria dell'Informazione, I-81031 Aversa (CE) Italy. NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
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Ultimately short ballistic vertical graphene Josephson junctions. Nat Commun 2015; 6:6181. [PMID: 25635386 PMCID: PMC4317505 DOI: 10.1038/ncomms7181] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Accepted: 12/27/2014] [Indexed: 11/26/2022] Open
Abstract
Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale. The functionality of Josephson junctions—a thin insulating layer between two superconducting regions—is greatly enhanced by using hybrid material systems. Here, the authors incorporate graphene into a Josephson junction and demonstrate ballistic transport through the atom-thick layer.
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Li M, Yao Y, Ding J, Liu L, Qin J, Zhao Y, Hou H, Fan Y. Spectroscopic and crystallographic investigations of novel BODIPY-derived metal-organic frameworks. Inorg Chem 2015; 54:1346-53. [PMID: 25587884 DOI: 10.1021/ic502219y] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
To explore new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-derived metal-organic frameworks (MOFs), we employed 2,6-dicarboxyl-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene (H2L) as a ligand to successfully synthesize five coordination polymers, namely, {[Zn2(L)2(bpp)]·2H2O·2EtOH}n (1), {[Cd2(L)2(bpp)]·2H2O·EtOH}n (2), {[Cd2(L)(bpe)3(NO3)2]·2H2O·DMF·EtOH}n (3), {[Cd(L)(bpe)0.5(DMF)(H2O)]}n (4), and {[Cd(L)(bpe)0.5]·1.5H2O·DMF}n (5) (bpp = 1,3-bi(4-pyridyl)propane, bpe = 1,2-bi(4-pyridyl)ethane). Except for two 2D-layer coordination polymers 3 and 4, the rest samples exhibit 3D metal-organic frameworks with certain pore sizes, especially MOFs 1 and 5. Spectroscopic and crystallographic investigations demonstrate that the absorption and emission energies of the BODIPY chromophores are sensitive to the coordination modes. Moreover, in case 2, the transition metal centers coordinated with the dicarboxylate ligands L(2-) are capable of forming the two BODIPY units in coplanar arrangements (θ = 37.9°), simultaneously suppressing the uncommon J-dimer absorption band centered at 705 nm with a long tail into the near-infrared region at room temperature. On the other hand, in comparison with the ligand H2L, the emission of monomer-like BODIPY in case 3 is enhanced in the solid state by a considerably long distance between the parallel BODIPY planes (about 14.0 Å).
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Affiliation(s)
- Ming Li
- College of Chemistry and Molecular Engineering, Zhengzhou University , Henan 450001, China
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Ki DK, Fal'ko VI, Abanin DA, Morpurgo AF. Observation of even denominator fractional quantum Hall effect in suspended bilayer graphene. NANO LETTERS 2014; 14:2135-2139. [PMID: 24611523 DOI: 10.1021/nl5003922] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We investigate low-temperature magneto-transport in recently developed, high-quality multiterminal suspended bilayer graphene devices, enabling the independent measurement of the longitudinal and transverse resistance. We observe clear signatures of the fractional quantum Hall effect with different states that are either fully developed, and exhibit a clear plateau in the transverse resistance with a concomitant dip in longitudinal resistance or incipient, and exhibit only a longitudinal resistance minimum. All observed states scale as a function of filling factor ν, as expected. An unprecedented even-denominator fractional state is observed at ν = -1/2 on the hole side, exhibiting a clear plateau in Rxy quantized at the expected value of 2h/e(2) with a precision of ∼0.5%. Many of our observations, together with a recent electronic compressibility measurement performed in graphene bilayers on hexagonal boron-nitride (hBN) substrates, are consistent with a recent theory that accounts for the effect of the degeneracy between the N = 0 and N = 1 Landau levels in the fractional quantum Hall effect and predicts the occurrence of a Moore-Read type ν = -1/2 state. Owing to the experimental flexibility of bilayer graphene, which has a gate-dependent band structure, can be easily accessed by scanning probes, and can be contacted with materials such as superconductors, our findings offer new possibilities to explore the microscopic nature of even-denominator fractional quantum Hall effect.
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Affiliation(s)
- Dong-Keun Ki
- Départment de Physique de la Matiére Condensée (DPMC) and Group of Applied Physics (GAP), University of Geneva , 24 Quai Ernest-Ansermet, CH1211 Genéve 4 Switzerland
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