Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene

Shalom, M. Ben; Zhu, Mengjian; Fal’ko, Vladimir I.; Mishchenko, Artem; Kretinin, A. V.; Новоселов, К. С.; Woods, Colin R.; Watanabe, Kenji; Taniguchi, Takashi; Geǐm, A. K.; Prance, Jonathan

doi:10.1038/nphys3592

Cited by 225 publications

(294 citation statements)

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“…A PMMA mask defining the shape of the device was fabricated on top of the annealed hBN-graphene-hBN stack by electron-beam lithography. The stack was etched in O 2 /CHF 3 plasma with fast selective removal of hBN 46 . Metallic contacts (Niobium) were implemented in a second stage where an additional PMMA mask was used for both etching the stack and for the metal lift-off 46 .…”

Section: S12 Hbn Encapsulated Graphene Device Fabricationmentioning

confidence: 99%

“…The stack was etched in O 2 /CHF 3 plasma with fast selective removal of hBN 46 . Metallic contacts (Niobium) were implemented in a second stage where an additional PMMA mask was used for both etching the stack and for the metal lift-off 46 . This procedure is similar to previous reports and results in electrons mobility above 30 2 • ⁄ and ballistic transport on length scale of many microns 28,47 .…”

Section: S12 Hbn Encapsulated Graphene Device Fabricationmentioning

confidence: 99%

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Nanoscale thermal imaging of dissipation in quantum systems

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et al. 2016

Nature

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Energy dissipation is a fundamental process governing the dynamics of physical, chemical, and biological systems. It is also one of the main characteristics distinguishing quantum and classical phenomena. In condensed matter physics, in particular, scattering mechanisms, loss of quantum information, or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. Despite its vital importance the microscopic behavior of a system is usually not formulated in terms of dissipation because the latter is not a readily measureable quantity on the microscale. Although nanoscale thermometry is gaining much recent interest [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] , the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation required for study of quantum systems. Here we report a superconducting quantum interference nano-thermometer device with sub 50 nm diameter that resides at the apex of a sharp pipette and provides scanning cryogenic thermal sensing with four orders of magnitude improved thermal sensitivity of below 1 µK/Hz 1/2 . The non-contact non-invasive thermometry allows thermal imaging of very low nanoscale energy dissipation down to the fundamental Landauer limit [16][17][18] of 40 fW for continuous readout of a single qubit at 1 GHz at 4.2 K. These advances enable observation of dissipation due to single electron charging of individual quantum dots in carbon nanotubes and reveal a novel dissipation mechanism due to resonant localized states in hBN encapsulated graphene, opening the door to direct imaging of nanoscale dissipation processes in quantum matter. 2 Investigation of energy dissipation on the nanoscale is of major fundamental interest for a wide range of disciplines from biological processes, through chemical reactions, to energy-efficient computing [1][2][3][4][5] . Study of dissipation mechanisms in quantum systems is of particular importance because dissipation demolishes quantum information. In order to preserve a quantum state the dissipation has to be extremely weak and hence hard to measure. As a figure of merit for detection of low power dissipation in quantum systems 16 we consider an ideal qubit operating at a typical readout frequency of 1 GHz. Landauer's principle states the lowest bound on energy dissipation in an irreversible qubit operation to be 0 = B ln 2, where B is Boltzmann's constant and is the temperature 17,18 . At = 4.2 K, 0 = 410 -23 J, several orders of magnitude below 10 -19 J of dissipation per logical operation in present day superconducting electronics and 10 -15 J in CMOS devices 19,20 . Hence the power dissipated by an ideal qubit operating at a readout rate of = 1 GHz will be as low as = 0 = 40.2 fW. The resulting temperature increase of the qubit will depend on its size and the thermal properties of the substrate. For example, a 120 × 120 nm 2 device on a 1 µm thick SiO 2 /Si substrate dissipating 40 fW will heat up by about 3 µK (Fig. 1). Suc...

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Section: S12 Hbn Encapsulated Graphene Device Fabricationmentioning

confidence: 99%

Section: S12 Hbn Encapsulated Graphene Device Fabricationmentioning

confidence: 99%

Nanoscale thermal imaging of dissipation in quantum systems

Halbertal

Cuppens

Shalom

et al. 2016

Nature

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197

175

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“…These properties, combined with the ability to control the number of conduction channels with a gate voltage, make graphene an ideal test-bed for exploring Andreev physics in two dimensions (2D). Although the superconducting proximity effect in graphene has attracted considerable research interest [19][20][21][22][23][24][25][26][27][28][29] , most of the experimental studies have been limited to transport measurements of dissipationless supercurrent in graphene-based (S-G-S) Josephson junctions. Accessing the energy domain while controlling the superconducting phase difference is crucial for probing ABS, and it has been performed in just a few systems, such as silver wires 9 , carbon nanotubes 10 , semiconductor nanowires 11 , and atomic breakjunctions 12,13 .…”

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“…1c and depends on geometric and microscopic parameters 7,8 , such as the conductor dimensions that determine the number of ABS, the scattering processes in the conductor and the contact's transparency. Strong ABS phase dependence, and therefore a prominent proximity effect, is achieved in ballistic systems with transparent N/S interfaces 7,8 .Graphene (G) can exhibit low contact resistance and weak scattering when connected to superconducting electrodes 19,20 . These properties, combined with the ability to control the number of conduction channels with a gate voltage, make graphene an ideal test-bed for exploring Andreev physics in two dimensions (2D).…”

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Tunnelling spectroscopy of Andreev states in graphene

et al. 2017

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A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties 1,2 . This proximity e ect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states [3][4][5][6][7][8] . Spectroscopic studies of Andreev states have been performed in just a handful of systems 9-13 . The unique geometry, electronic structure and high mobility of graphene 14,15 make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity e ect in superconductor-graphenesuperconductor junctions. The measured energy spectra, which depend on the phase di erence between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between di erent mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent-phase relation in a tunnelling experiment, thus establishing the connection between Andreev physics at finite energy and the Josephson e ect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials [16][17][18] .When a normal quantum conductor (N) is sandwiched between two superconductors (S), a current can flow in the absence of any voltage, due to the Josephson effect 1 . This macroscopic supercurrent is driven by the difference between the order parameter phases of the two superconductors, ϕ. Microscopically, it corresponds to the coherent flow of Cooper pairs through the conductor, which is made possible by successive Andreev reflections at the N/S interfaces, where electrons (holes) are reflected as oppositespin holes (electrons) (Fig. 1a). Due to this process, resonant electron-hole states form in the central conductor, known as Andreev bound states (ABS) 3-6 . They lie as energy levels inside the superconducting gap [−∆, ∆], only negative-energy states being populated in the ground state (Fig. 1b). Crucially, the Andreev energy E n (ϕ) depends on ϕ, and each populated ABS carries in response a supercurrent (1/φ 0 )(∂E n /∂ϕ), where φ 0 = /2e is the reduced flux quantum, with the reduced Planck constant and e the elementary charge. The overall phase-dependent Andreev spectrum is shown in Fig. 1c and depends on geometric and microscopic parameters 7,8 , such as the conductor dimensions that determine the number of ABS, the scattering processes in the conductor and the contact's transparency. Strong ABS phase dependence, and therefore a prominent proximity effect, is achieved in ballistic systems with transparent N/S interfaces 7,8 .Graphene (G) can exhibit low contact resistance and weak scattering when connected to superconducting electrodes 19,20 . These properties, combined with t...

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Van der Waals Heterostructures for High‐Performance Device Applications: Challenges and Opportunities

et al. 2019

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Discovery of two-dimensional materials with unique electronic, superior optoelectronic or intrinsic magnetic order have triggered worldwide interests among the fields of material science, condensed matter physics and device physics. Vertically stacking of twodimensional materials with distinct electronic and optical as well as magnetic properties enables to create a large variety of van der Waals heterostructures. The diverse properties of the vertical heterostructures open up unprecedented opportunities for various kinds of device applications, e.g. vertical field effect transistors, ultrasensitive infrared photodetectors, spin-filtering devices and so on, which are inaccessible in the conventional material heterostructures. Here, we review the current status of vertical heterostructures device applications in vertical transistors, infrared photodetectors and spintronic memory/transistors. The relevant challenges for achieving highperformance devices are presented. We also provide outlook on future development of vertical heterostructure devices with integrated electronic and optoelectronic as well as spintronic functinalities.

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Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene

Cited by 225 publications

References 27 publications

Nanoscale thermal imaging of dissipation in quantum systems

Nanoscale thermal imaging of dissipation in quantum systems

Tunnelling spectroscopy of Andreev states in graphene

Van der Waals Heterostructures for High‐Performance Device Applications: Challenges and Opportunities

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