Dear  Dinesh Kumar,

If you want to find something about flux creep in low T superconductors, you must look for it in papers of 1963-1980 years.  Now the most of LT colleagues know that  it was unsufficient idea of P.Anderson.  It is pity that my HT colleagues  have gotten their knowleges from antiquated monographies and are repeating all the mistakes.  You can find the modern view in my RG list. For example: "Resistance-Current curves of high Pinning Superconductors", "Electrodynamics of High Pinning Superconductors", "Electrodynamics of multifilament superconductors ".

With the best regards, E.Klimenko.

Different models were used to explain the dissipative behavior such as the collective creep model, thermally assisted flux flow, and thermal fluctuations, but none of them was successful in explaining exactly the dissipation mechanism. In most of the published papers, the thermally assisted flux flow (TAAF) theory is usually used, where the ρ(T,H) curves can be described by the Arrhenius equation ρ(T,H) = ρn exp(−U0/KBT ), with ρn being the normal state resistivity and U0 the activation energy.

@ E.Yu. Klimenko

Dear Sir,

I am going through number of old papers (e.g. by Beasley and by Palstra). I will also go through your papers and try to understand more.

Sincerely,

Dinesh

@Yazid Boudjadja

Dear Yazid,

I have gone through those papers that mentions about this relation, I still want to confirm if we can use it  for both HTSC and LTSCs. Basically I am trying to ask what are the do's and don'ts in using TAFF model.

Thanking you.

Sincerely,

Dinesh

@Yazid Boudjadja

Can I get a pdf copy of your thesis? if it is okay.

My email ID is 

[email protected]

Resistance measurements in applied magnetic field can be worked out by so-called Arrhenius plots, which enable to determine a pinning potential, U0. This works in all types of superconductors, but we have to consider the critical fields, Hc2(T) and Hirr(T). Hc2(T) is the thermodynamic upper critical field, where the superconductivity is destroyed. The irreversibility field, Hirr(T), is defined as the place where U0 -> 0; thus the flux pinning is vanishing above Hirr(T). H_irr(T) contains all the information about the flux pinning landscape (the various pinning potentials), and the dimensionality of the vortices (extended stiff vortices vs. layered pancake vortices, single vortices, vortex bundles, etc.).

As a result, for samples with stiff extended vortices and a large single vortex regime, Hirr(T) will be almost equal to Hc2(T). This is the case for most "conventional" superconductors having a low Tc, so there was no need to discuss the effects of flux creep so much as in the case of the HTSC systems.

But also the flux creep theory was established at the end of the 1960s (Anderson and Kim), which implies that also for conventional systems this may deliver important information. Layered low-Tc superconductors like NbSe2 or MoGe were studied quite often in this direction, and also artificially layered systems like Nb/Cu multilayers (see for example Y.G. Xiao et al., Physica  C 224 (1994) 240).

Dear Dinesh , recently we measured Uo by ac susceptibility. Please find enclosed our paper. If you need we can manage measurements in our laboratory

@Michael Rudolf Koblischka

Dear Sir,

First of all, let me thank you for coming straight to the point. My confidence on this topic have been boosted after reading your answer.

I still have some more questions for you,

"This works in all types of superconductors, but we have to consider the critical fields, Hc2(T) and Hirr(T)"

Does it mean that, Flux creep exist between Hirr to Hc2? Or, does only flux flow exist between these two fields?

"The irreversibility field, Hirr(T), is defined as the place where U0 -> 0; thus the flux pinning is vanishing above Hirr(T), thus the flux pinning is vanishing above Hirr(T)"

Can the Hirr be considered by 10% of the resistivity criteria, Just as we consider Hc2 by 90% criteria?

Sincerely,

Dinesh

@Daniele Rinaldi

Dear Sir,

Thank you so much for the paper you have sent.

Sincerely,

Dinesh

Dear Dinesh  and Daniele,

I have read the paper with interest. It is really high quality work.  However I have not found any approvement of thermal activation process.  And it was never approved anywhere!   It is possible to describe any experiment with any theory, if you allow dependence of theory constants on temperature, magnetic field an so on. A lot of our colleagues are doing it during a half of century  using  P.Anderson model.

I guess that it is pinning inhomogeneity that responsible for V(I) curve smoothness. So it is necessary to study pinning energy in a volume unit. The critical Lorentz force depends also on steepness of averaged potential barrier.  This notion allowed me to describe the anisotropy of critical Lorentz force.  It depends not only on  pinning energy (depending on magnetic field direction) but also on direction of magnetic flux movement.

My best regards, EK.

Dear Dinesh,

let me recommend you an article, where a comparison of critical current between LT and HT superconductors is given.

D. Dew-Hughes, Low Temp. Phys. v.27 (2001) p.713

Best regards,

Elena

Dear Dinesh,

Uo is parameter  from Anderson's flux creep  model. This joke of genius was incorrect from the very beginning. It was popular some time but never approved by experiment. Moreover it was ruled out by Mitin (Zh.Exp.Theor .Phys 93, 590,(1987)) who had discovered the finite rate of field decay at very low temperatures. To our regret he didn't resist the templation to invent a new equally incorrect mechanism (fluxoid tunnelling). Most of researchers understood uselessness of the model for experiments treatment  (1970-80).  So you hardly saw the papers. The new HTSC generation  had studied the problem from outdated books. And the history began once again. It is slightest misfortune from those  were brought by HTSC stock-jobbing to applied superconductivity. You will find some detailes in my paper "Resistance-Current Curves of High Pinning Superconductors", J.Exp.Theor.Phys. 100, 50-65(2005).

Various models were used to explain the dissipative behavior in superconducting materials; such as the flux creep model, thermally assisted flux flow, and thermal fluctuations. Resistance measurements in applied magnetic field can be worked out by so-called Arrhenius plots, which enable to determine a pinning potential, U0. The thermally assisted flux flow (TAAF) theory is usually used, where the ρ(T,H) curves can be described by the Arrhenius equation ρ(T,H) = ρn exp(−U0/KBT ), where ρn is the normal state resistivity and U0 is the activation energy.

Furthermore, none of these models was successful in explaining exactly the dissipation mechanism. Uo is parameter  from Anderson's flux creep  model. This joke of genius was incorrect from the very beginning. It was popular some time but never approved by experiment.

According to me, for most "conventional" superconductors having a low Tc, there was no need to discuss the effects of flux creep so much as in the case of the HTSC systems.