Browsing by Subject "WIRES"

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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
Switching currents limited by single phase slips in one-dimensional superconducting Al nanowires.
(Physical review letters, 2011-09-21) Li, Peng; Wu, Phillip M; Bomze, Yuriy; Borzenets, Ivan V; Finkelstein, Gleb; Chang, AM
An aluminum nanowire switches from superconducting to normal as the current is increased in an upsweep. The switching current (I(s)) averaged over upsweeps approximately follows the depairing critical current (I(c)) but falls below it. Fluctuations in I(s) exhibit three distinct regions of behaviors and are nonmonotonic in temperature: saturation well below the critical temperature T(c), an increase as T(2/3) at intermediate temperatures, and a rapid decrease close to T(c). Heat dissipation analysis indicates that a single phase slip is able to trigger switching at low and intermediate temperatures, whereby the T(2/3) dependence arises from the thermal activation of a phase slip, while saturation at low temperatures provides striking evidence that the phase slips by macroscopic quantum tunneling.