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> Nanotech forum > Nanotech > Chakravarty-Schmid (CS) quantum transition in superconducting shunted wires and junctions
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Chakravarty-Schmid (CS) quantum transition in superconducting shunted wires and junctions |
Alexey
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Mon Apr 2 04:58:18 2007
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Chakravarty-Schmid (CS) quantum transition in superconducting shunted wires and junctions |
The Chakravarty-Schmid transition is a superconductor-insulator quantum transition, predicted for shunted Josephson junctions. It occurs as the shunting resistance becomes larger than h/(4e^2).
Intro taken from Khlebnikov and Pryadko paper PRL 95, 107007 (2005):
The possibility that quantum fluctuations destroy superconductivity
in thin wires has attracted the attention of both
experimentalists and theorists for a long time. Similarly to
Little’s analysis of thermal fluctuations, one concludes
that the requisite quantum fluctuation should be sufficiently large, so as to allow the Ginzburg-Landau (GL)
order parameter to vanish at the core, and the phase of
GL to unwind. Such fluctuations are known as quantum
phase slips (QPSs). On the experimental side, there has
been a bit of controversy over precisely how superconductivity disappears in thin wires at low temperatures. Some
experiments see a sharp superconducting-insulator transition
(SIT), while others do not.
One issue to be discussed:
The CS phase transition involves a power-law T-dependence of resistance on the superconducting side. Buchler et al. have found this universality class by attaching an effective resistor to the wire's ends. Pryadko and Khlebnikov have found an intrinsic mechanism for such behavior, published in PRL 95, 107007, 2005. The universality class is identified in this paper as that of the dissipative quantum mechanics. Plasmon mode (i.e. Mooij-Schon mode) is essentially involved in the Khlebnikov-Pryadko (KP) theory. The mode should be gapless. The questions to be discussed: should CS transition be observed in short wires also, even in weak links perhaps? The Mooij-Schon mode can be gapped in the wires, thus making QPS decoupled from the plasmons.
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| Created: Mon Apr 2 23:51:20 2007
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Alexey
Join Date:
Mon Apr 2 04:58:18 2007
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NEW THEORY OF SIT |
A new theory of QPS in nanowires was published recently:
http://www.nanogallery.info/filez/Meidan-Oreg-Refael%20PRL%20paper.pdf
See the link above where a theory by Meidan, Oreg, and Refael is presented.
The theory can generate R(T) curves which fit the Bollinger et al. data impressively well.
THUS THE EXISTENCE OF QPS IS STRONGLY SUGGESTED.
A QUESTION REMAINS: CAN ONE PERFORM AN MQT EXPERIMENT AS WAS DONE BY CLARKE, MARTINIS, AND DEVORET:
http://www.nanogallery.info/filez/Clarke-MQT.pdf
AND ESTABLISH THE EXISTENCE OF DISCRETE QUANTUM LEVELS IN NANOWIRES.
IN OTHER WORDS, CAN ONE EXPECT, BASED ON THE THEORY, THAT ENERGY STATES OF A SHORT NANOWIRES ARE QUANTIZED, AS IS THE CASE IN SMALL JOSEPHSON JUNCTIONS, AS WAS PROVEN BY CLARKE, MARTINIS, AND DEVORET?
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| Created: Fri May 4 08:36:05 2007
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AB
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Thu Jun 21 22:16:59 2007
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RE: Chakravarty-Schmid (CS) quantum transition in superconducting shunted wires and junctions |
| One more question: how the high-frequency resistance of the leads should be calculated? Why is it not 50 Ohms (as is usual for a transmission line) but a few kOhms? Is this a boundary effect? |
| Created: Thu Jun 21 22:21:28 2007
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AB
Join Date:
Thu Jun 21 22:16:59 2007
Posts:6
Reputation:10
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RE: Chakravarty-Schmid (CS) quantum transition in superconducting shunted wires and junctions |
| "boundary effect" means here the point of connection of the nanowire to the lead. At this point there may be a mismatch of impedances. Thus the waves might be reflected?? |
| Created: Thu Jun 21 22:22:53 2007
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