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Clem, John R

Publications and source records attributed to Clem, John R.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Inductances and attenuation constant for a thin-film superconducting coplanar waveguide resonator

The geometric, kinetic, and total inductances and the attenuation constant are theoretically analyzed for a thin-film superconducting coplanar waveguide resonator consisting of a current-carrying central conductor, adjacent slots, and ground planes that return the current. The analysis focuses on films of thickness d obeying d<2λ (λ is the London penetration depth), for which the material properties are characterized by the two-dimensional screening length Λ = 2λ2/d. Introducing a cut-off procedure that guarantees that the magnitudes of the currents in the central conductor and the ground planes are equal, new and simpler results are obtained for the kinetic inductance and the attenuation constant for small Λ. Exact results for arbitrary Λ are presented for the geometric, kinetic, and total inductances in the limit of tiny slot widths, and approximate results are presented for arbitrary slot widths.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Geometry-dependent critical currents in superconducting nanocircuits

In this paper, we calculate the critical currents in thin superconducting strips with sharp right-angle turns, 180{sup o} turnarounds, and more complicated geometries, where all the line widths are much smaller than the Pearl length {Lambda} = 2{lambda}{sup 2}/d. We define the critical current as the current that reduces the Gibbs-free-energy barrier to zero. We show that current crowding, which occurs whenever the current rounds a sharp turn, tends to reduce the critical current, but we also show that when the radius of curvature is less than the coherence length, this effect is partially compensated by a radius-of-curvature effect. We propose several patterns with rounded corners to avoid critical-current reduction due to current crowding. These results are relevant to superconducting nanowire single-photon detectors, where they suggest a means of improving the bias conditions and reducing dark counts. These results also have relevance to normal-metal nanocircuits, as these patterns can reduce the electrical resistance, electromigration, and hot spots caused by nonuniform heating.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

A nanoscale SQUID operating at high magnetic fields

A washer-free Nb nanoSQUID has been developed for measuring magnetization changes from nanoscale objects. The SQUID loop is etched into a 250 nm wide Au/Nb bilayer track and the diameter of the SQUID hole is ~ 70 nm. In the presence of a magnetic field perpendicular to the plane of the SQUID, vortex penetration into the 250 nm wide track can be observed via the critical current–applied field characteristic and the value at which vortex first penetrates is consistent with the theoretical prediction. Upon removing the applied field, the penetrated vortices escape the track and the critical current at zero field is restored.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Effect of nearby Pearl vortices upon the Ic versus B characteristics of planar Josephson junctions in thin and narrow superconducting strips

In this paper I show how to calculate the effect of a nearby Pearl vortex or antivortex upon the critical current I{sub c}(B) when a perpendicular magnetic induction B is applied to a planar Josephson junction in a long, thin, superconducting strip of width W much less than the Pearl length {Lambda} = 2{lambda}2/d, where {lambda} is the London penetration depth and d is the thickness (d < {lambda}). The theoretical results provide a qualitative explanation of unusual features recently observed experimentally by Golod et al. [ Phys. Rev. Lett. 104 227003 (2010)] in a device with a similar geometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Corbino-geometry Josephson weak links in thin superconducting films

I consider a Corbino-geometry superconducting-normal-superconducting Josephson weak link in a thin superconducting film, in which current enters at the origin, flows outward, passes through an annular Josephson weak link, and leaves radially. In contrast to sandwich-type annular Josephson junctions, in which the gauge-invariant phase difference obeys the sine-Gordon equation, here the gauge-invariant phase difference obeys an integral equation. I present exact solutions for the gauge-invariant phase difference across the weak link when it contains an integral number N of Josephson vortices and the current is zero. I then study the dynamics when a current is applied, and I derive the effective resistance and the viscous drag coefficient; I compare these results with those in sandwich-type junctions. I also calculate the critical current when there is no Josephson vortex in the weak link but there is a Pearl vortex nearby.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

Josephson junctions in thin and narrow rectangular superconducting strips

I consider a Josephson junction crossing the middle of a thin rectangular superconducting strip of length L and width W subjected to a perpendicular magnetic induction B. I calculate the spatial dependence of the gauge-invariant phase difference across the junction and the resulting B dependence of the critical current I{sub c}(B).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗