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> Nanotech forum > Nanotech > Size of phase slips in superconducting nanowires
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Size of phase slips in superconducting nanowires |
Alexey
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RE: Size of phase slips in superconducting nanowires |
| no contradiction I think. It is calculated using GL equations that the length of a phase slip is about 2ksi. But this is done in classical limit. In the quantum limit the queston is not so clear, since one does not minimize the GL free energy functional but one needs to minimize the action. This might give much large dimensions for phase slips. |
| Created: Mon Apr 30 01:46:36 2007
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Alexey
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RE: Size of phase slips in superconducting nanowires |
also, the formula I gave is an approximation. Langer and Ambegaokar did an exact calculation of the energy of a phase slip based on GL equations etc. They got the result which approximately agrees with the estimation deltaF=A*ksi(T)*Hc^2/8Pi.
But as I said, this was a classical (not quantum) calculation of course. |
| Created: Mon Apr 30 01:49:26 2007
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Physya The Cat
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RE: Size of phase slips in superconducting nanowires |
| also valid only near Tc |
| Created: Mon May 7 05:45:13 2007
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Kostia
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Fri May 25 18:59:39 2007
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RE: Size of phase slips in superconducting nanowires |
My understanding is that the whole concept of PS is defined in the limit
deltaF << Delta < kT ~ kTc. During each PS event this energy difference deltaF is released contributing to finite resitance or/and Josephson radiation and/or propagation of Mooij-Shoen wave etc. = dissipation. But the process happens on the scale of the responce time of the superconducting system h/Delta << h/deltaF.
Size of the PS is again "by definition" of a fluctuation is determined by the physical scale of the MINIMUM size of a statistically independent sub-system. Hence, it is ~ksi. If one starts to speak about domains >> ksi, than it is not already a fluctuation, but a hot-spot formation.
However, the most intriguing here is not the size of the core, but the effective size of the disturbance produced by the PS. This is related to the quasiparticle charge imbalance and might be indeed >> ksi. |
| Created: Fri May 25 20:08:37 2007
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Kostia
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ERRARTUM |
| Have written nonsence :) The correct applicability condition is deltaF > kT > Delta(T). If it would be opposite, superconductivity cannot be killed at all. Hence, the responce time of the superconducting system (when gap is restored) is h/Delta >> h/deltaF, where the last time characterises the transition time between two quantum states: 2pi x n and 2pi x (n+/-1). |
| Created: Fri May 25 21:09:57 2007
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Alexey
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RE: Size of phase slips in superconducting nanowires |
OK, but what about quantum phase slips? Do they have a normal core? Do you think it would be ~ksi also? I understand that this size scale is derived by minimizing the free energy of the wire, under the assumption that order parameter is zero at one point. But if you start talking about quantum phase slips, the result might be different since in this case one needs to minimize the action for an event, but not simply the free energy. This is what I understood after discussing with Khlebnikov some time ago.
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| Created: Wed May 30 22:46:22 2007
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Kostia
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RE: Size of phase slips in superconducting nanowires |
I do not understand such subtelness :) In my opinion PS momentary zeroes Delta somewhere along the wire. Minimum size is still ksi.
By the way exact answer on your former question about enegy difference before and after PS: Langer-Ambegaokar, Eq(2.10) |
| Created: Wed May 30 23:21:32 2007
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Kostia
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RE: Size of phase slips in superconducting nanowires |
| To the attention of experimentalists: PHYSICAL REVIEW B 75, 172509 2007 |
| Created: Thu May 31 16:59:57 2007
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Alexey
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RE: Size of phase slips in superconducting nanowires |
That is a very interesting paper. I see it touches the subject of homogeneity. This subjects interests me very much. We also did some work on this. We tried to see how the SIT observed in homogeneous wires changes if one goes to inhomogeneous wires. It turns out that in non-homogeneous wires there is no clear SIT transition and sample can show a mixed behavior, with signatures of superconducting and insulation types of behavior in the same sample. Some samples showed even some tails which could be understood as caused by QPS, but in our case it was probably weak links, since, as I said, we used a set of wires which were made inhomogeneous deliberately.
Here the link:
http://research.physics.uiuc.edu/Bezryadin/Pubs/Bollinger-RapidCom.pdf
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| Created: Sat Jun 9 18:54:15 2007
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