Browsing by Author "Bomze, Y"

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Open Access
Anomalous periodicity of magnetic interference patterns in encapsulated graphene Josephson junctions
(Physical Review Research) Ke, CT; Draelos, AW; Seredinski, A; Wei, MT; Li, H; Hernandez-Rivera, M; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Bomze, Y; Borzenets, IV; Amet, F; Finkelstein, G
Open Access
Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes.
(Physical review letters, 2016-12-02) Borzenets, IV; Amet, F; Ke, CT; Draelos, AW; Wei, MT; Seredinski, A; Watanabe, K; Taniguchi, T; Bomze, Y; Yamamoto, M; Tarucha, S; Finkelstein, G
We investigate the critical current I_{C} of ballistic Josephson junctions made of encapsulated graphene-boron-nitride heterostructures. We observe a crossover from the short to the long junction regimes as the length of the device increases. In long ballistic junctions, I_{C} is found to scale as ∝exp(-k_{B}T/δE). The extracted energies δE are independent of the carrier density and proportional to the level spacing of the ballistic cavity. As T→0 the critical current of a long (or short) junction saturates at a level determined by the product of δE (or Δ) and the number of the junction's transversal modes.
Open Access
Retrapping current, self-heating, and hysteretic current-voltage characteristics in ultranarrow superconducting aluminum nanowires
(Physical Review B - Condensed Matter and Materials Physics, 2011-11-08) Li, P; Wu, PM; Bomze, Y; Borzenets, IV; Finkelstein, G; Chang, AM
Hysteretic I-V (current-voltage) curves are studied in narrow Al nanowires. The nanowires have a cross section as small as 50 nm2. We focus on the retrapping current in a down-sweep of the current, at which a nanowire re-enters the superconducting state from a normal state. The retrapping current is found to be significantly smaller than the switching current at which the nanowire switches into the normal state from a superconducting state during a current up-sweep. For wires of different lengths, we analyze the heat removal due to various processes, including electron and phonon processes. For a short wire 1.5μm in length, electronic thermal conduction is effective; for longer wires 10μm in length, phonon conduction becomes important. We demonstrate that the measured retrapping current as a function of temperature can be quantitatively accounted for by the self-heating occurring in the normal portions of the nanowires to better than 20% accuracy. For the phonon processes, the extracted thermal conduction parameters support the notion of a reduced phase-space below three dimensions, consistent with the phonon thermal wavelength having exceeded the lateral dimensions at temperatures below ∼1.3 K. Nevertheless, surprisingly the best fit was achieved with a functional form corresponding to three-dimensional phonons, albeit requiring parameters far exceeding known values in the literature. © 2011 American Physical Society.
Open Access
Supercurrent in the quantum Hall regime.
(Science (New York, N.Y.), 2016-05) Amet, F; Ke, CT; Borzenets, IV; Wang, J; Watanabe, K; Taniguchi, T; Deacon, RS; Yamamoto, M; Bomze, Y; Tarucha, S; Finkelstein, G
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.
Open Access
Two-stage Kondo effect and Kondo-box level spectroscopy in a carbon nanotube
(Physical Review B - Condensed Matter and Materials Physics, 2010-10-18) Bomze, Y; Borzenets, I; Mebrahtu, H; Makarovski, A; Baranger, HU; Finkelstein, G
The concept of the "Kondo box" describes a single spin, antiferromagnetically coupled to a quantum dot with a finite level spacing. Here, a Kondo box is formed in a carbon nanotube interacting with a localized electron. We investigate the spins of its first few eigenstates and compare them to a recent theory. In an "open" Kondo-box, strongly coupled to the leads, we observe a nonmonotonic temperature dependence of the nanotube conductance, which results from a competition between the Kondo-box singlet and the "conventional" Kondo state that couples the nanotube to the leads. © 2010 The American Physical Society.