38 research outputs found
Quantum fluctuations in thin superconducting wires of finite length
In one dimensional wires, fluctuations destroy superconducting long-range
order and stiffness at finite temperatures; in an infinite wire, quasi-long
range order and stiffness survive at zero temperature if the wire's
dimensionless admittance is large, . We analyze the
disappearance of this superconductor-insulator quantum phase transition in a
finite wire and its resurrection due to the wire's coupling to its environment
characterized through the dimensionless conductance . Integrating over phase
slips, we determine the flow of couplings and establish the -- phase
diagram.Comment: 4 pages, 2 figure
Negative magnetoresistance of ultra-narrow superconducting nanowires in the resistive state
We present a phenomenological model qualitatively explaining negative
magnetoresistance in quasi-one-dimensional superconducting channels in the
resistive state. The model is based on the assumption that fluctuations of the
order parameter (phase slips) are responsible for the finite effective
resistance of a narrow superconducting wire sufficiently close to the critical
temperature. Each fluctuation is accompanied by an instant formation of a
quasi-normal region of the order of the non-equilibrium quasiparticle
relaxation length 'pinned' to the core of the phase slip. The effective
time-averaged voltage measured in experiment is a sum of two terms. First one
is the conventional contribution linked to the rate of the fluctuations via the
Josephson relation. Second term is the Ohmic contribution of this quasi-normal
region. Depending on material properties of the wire, there might be a range of
magnetic fields where the first term is not much affected, while the second
term is effectively suppressed contributing to the experimentally observed
negative magnetoresistance.Comment: 10 pages including 2 figure
The Breakdown of Alfven's Theorem in Ideal Plasma Flows
This paper presents both rigorous results and physical theory on the
breakdown of magnetic flux conservation for ideal plasmas, by nonlinear
effects. Our analysis is based upon an effective equation for
magnetohydrodynamic (MHD) modes at length-scales with smaller scales
eliminated, as in renormalization-group methodology. We prove that
flux-conservation can be violated for an arbitrarily small length-scale
and in the absence of any non-ideality, but only if singular current sheets and
vortex sheets both exist and intersect in sets of large enough dimension. This
result gives analytical support to and rigorous constraints on theories of fast
turbulent reconnection. Mathematically, our theorem is analogous to Onsager's
result on energy dissipation anomaly in hydrodynamic turbulence. As a physical
phenomenon, the breakdown of magnetic-flux conservation in ideal MHD is similar
to the decay of magnetic flux through a narrow superconducting ring, by
phase-slip of quantized flux lines. The effect should be observable both in
numerical MHD simulations and in laboratory plasma experiments at moderately
high magnetic Reynolds numbers.Comment: 38 pages, 1 figur
Quantum Phase Slips in Superconducting Nanowires
We have measured the resistance vs. temperature of more than 20
superconducting nanowires with nominal widths ranging from 10 to 22 nm and
lengths from 100 nm to 1050 nm. With decreasing cross-sectional areas, the
wires display increasingly broad resistive transitions. The data are in very
good agreement with a model that includes both thermally activated phase slips
close to Tc and quantum phase slips (QPS) at low temperatures, but disagree
with an earlier model based on a critical value of R_n/Rq. Our measurements
provide strong evidence for QPS in thin superconducting wires.Comment: 9 pages, 3 figure
Quantum phase slip phenomenon in ultra-narrow superconducting nanorings
The smaller the system, typically - the higher is the impact of fluctuations.
In narrow superconducting wires sufficiently close to the critical temperature
Tc thermal fluctuations are responsible for the experimentally observable
finite resistance. Quite recently it became possible to fabricate sub-10 nm
superconducting structures, where the finite resistivity was reported within
the whole range of experimentally obtainable temperatures. The observation has
been associated with quantum fluctuations capable to quench zero resistivity in
superconducting nanowires even at temperatures T-->0. Here we demonstrate that
in tiny superconducting nanorings the same phenomenon is responsible for
suppression of another basic attribute of superconductivity - persistent
currents - dramatically affecting their magnitude, the period and the shape of
the current-phase relation. The effect is of fundamental importance
demonstrating the impact of quantum fluctuations on the ground state of a
macroscopically coherent system, and should be taken into consideration in
various nanoelectronic applications.Comment: 20 pages, 4 figure
Reply to the Comment on 'Quantum Phase Slips and Transport in Ultra-Thin Superconducting Wires'
We reply to the recent Comment [cond-mat/9702231] by J.-M. Duan. Our point of
view is markedly different on every issue raised. Much of the disagreement can
be traced to a different preception of experimentally relevant length scales.
i) We explain the difference between our formulation, which rests on a
microscopic basis, and the phenomenological one of the author. ii) Our
renormalization scheme is fundamentally right, as the "log(log)" interaction
appears only in wires of astronomical lengths. iii) The tunneling barrier is
profoundly reduced by the kinetic inductance. iv) We do make an appropriate
comparison to the data on the thinnest available wires.Comment: 1 page Revte
Gerda Newbower Collection 1998
The collection contains a questionnaire filled out by Gerda Newbower regarding her life in Austria before World War II, emigration from Austria to the United States, and life in the United States. Also included is a series of articles by Newbower about her emigration from Austria in 1938.digitizedGerda Newbower (formerly Neubauer) née Fantl was born on Feburary 6, 1910, in Vienna. She left Austria with her Leo Newbower husband in April 1938 and arrived in the United States in October 1938.An inventory is available in the folderAustrian Heritage Collectio