Browsing by Author "Wei, MT"
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Item 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, GItem 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, GWe 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.Item Open Access Chiral quasiparticle tunneling between quantum Hall edges in proximity with a superconductor(Physical Review B, 2019-09-10) Wei, MT; Draelos, AW; Seredinski, A; Ke, CT; Li, H; Mehta, Y; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Finkelstein, G; Amet, F; Borzenets, IV© 2019 American Physical Society. We study a two-terminal graphene Josephson junction with contacts shaped to form a narrow constriction, less than 100nm in length. The contacts are made from type-II superconducting contacts and able to withstand magnetic fields high enough to reach the quantum Hall regime in graphene. In this regime, the device conductance is determined by edge states, plus the contribution from the constricted region. In particular, the constriction area can support supercurrents up to fields of ∼2.5T. Additionally, enhanced conductance is observed through a wide range of magnetic fields and gate voltages. This additional conductance and the appearance of supercurrent is attributed to the tunneling between counterpropagating quantum Hall edge states along opposite superconducting contacts.Item Open Access Investigation of Supercurrent in the Quantum Hall Regime in Graphene Josephson Junctions(Journal of Low Temperature Physics, 2018-06-01) Draelos, A; Wei, MT; Seredinski, A; Ke, C; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Borzenets, I; Amet, F; Finkelstein, G© 2018, Springer Science+Business Media, LLC, part of Springer Nature. In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: (a) supercurrents independently flowing along both non-contacted edges of graphene mesa, and (b) opposite sides of the mesa being coupled by hybrid electron–hole modes flowing along the superconductor/graphene boundary. The supercurrent appears suppressed in extended junctions, suggesting the latter mechanism.Item Open Access Non-stokes drag coefficient in single-particle electrophoresis: New insights on a classical problem(Chinese Physics B, 2019-01-01) Liao, MJ; Wei, MT; Xu, SX; Daniel Ou-Yang, H; Sheng, PWe measured the intrinsic electrophoretic drag coefficient of a single charged particle by optically trapping the particle and applying an AC electric field, and found it to be markedly different from that of the Stokes drag. The drag coefficient, along with the measured electrical force, yield a mobility-zeta potential relation that agrees with the literature. By using the measured mobility as input, numerical calculations based on the Poisson-Nernst-Planck equations, coupled to the Navier-Stokes equation, reveal an intriguing microscopic electroosmotic flow near the particle surface, with a well-defined transition between an inner flow field and an outer flow field in the vicinity of electric double layer's outer boundary. This distinctive interface delineates the surface that gives the correct drag coefficient and the effective electric charge. The consistency between experiments and theoretical predictions provides new insights into the classic electrophoresis problem, and can shed light on new applications of electrophoresis to investigate biological nanoparticles.Item Open Access Subkelvin lateral thermal transport in diffusive graphene(Physical Review B, 2019-03-29) Draelos, AW; Silverman, A; Eniwaye, B; Arnault, EG; Ke, CT; Wei, MT; Vlassiouk, I; Borzenets, IV; Amet, F; Finkelstein, G© 2019 American Physical Society. In this work, we report on hot carrier diffusion in graphene across large enough length scales that the carriers are not thermalized across the crystal. The carriers are injected into graphene at one site and their thermal transport is studied as a function of applied power and distance from the heating source, up to tens of micrometers away. Superconducting contacts prevent out-diffusion of hot carriers to isolate the electron-phonon coupling as the sole channel for thermal relaxation. As local thermometers, we use the amplitude of the universal conductance fluctuations, which varies monotonically as a function of temperature. By measuring the electron temperature simultaneously along the length we observe a thermal gradient which results from the competition between electron-phonon cooling and lateral heat flow.Item Open Access Supercurrent in Graphene Josephson Junctions with Narrow Trenches in the Quantum Hall Regime(MRS Advances, 2018-01-01) Seredinski, A; Draelos, A; Wei, MT; Ke, CT; Fleming, T; Mehta, Y; Mancil, E; Li, H; Taniguchi, T; Watanabe, K; Tarucha, S; Yamamoto, M; Borzenets, IV; Amet, F; Finkelstein, G© 2018 Materials Research Society. Coupling superconductors to quantum Hall edge states is the subject of intense investigation as part of the ongoing search for non-abelian excitations. Our group has previously observed supercurrents of hundreds of picoamperes in graphene Josephson junctions in the quantum Hall regime. One of the explanations of this phenomenon involves the coupling of an electron edge state on one side of the junction to a hole edge state on the opposite side. In our previous samples, these states are separated by several microns. Here, a narrow trench perpendicular to the contacts creates counterpropagating quantum Hall edge channels tens of nanometres from each other. Transport measurements demonstrate a change in the low-field Fraunhofer interference pattern for trench devices and show a supercurrent in both trench and reference junctions in the quantum Hall regime. The trench junctions show no enhancement of quantum Hall supercurrent and an unexpected supercurrent periodicity with applied field, suggesting the need for further optimization of device parameters.