Level Correlations and Persistent Currents in Mesoscopic Metals (Sitotaw, Serota 1999) seems to be the most cited work in this field. And, honestly, it's over my head. It appears the material forms a single quantum state, and the current flow is an effect of resonance.johanfprins wrote:Do you not know that one can generate a permanently flowing curent around a mesoscopic ring of gold when the circumference of the ring is less than the mean free path? How do you explain this?WizWom wrote: No, even with an average free path length >> length, you will see measurable resistivity; because the mean path is a mean, with path lengths above and below. Those that fall within the length will generate resistivity.
Also, this occurs below a transition temperature only, that is, it is a superconducting effect.
As a first approximation, I would say that if the scale is a half or full wavelength of the ionization photon, then the system would tend to be stable, with photons exciting another atom within the structure.
Leakage current in a semiconductor is typically modeled as a resistive load to the leak drain.johanfprins wrote:Leakage or resistvity?This applies even when you are getting into the realm of quantum effects, its been observed in the 20 nm research parts, where the uncertainty principle contributes significant leakage in FETs.
Ah, now, you're trying to lead me down the garden path. The exclusion of magnetic fields is a side effect; electric fields are necessary for current flow. Electric fields are normalized throughout a conductor (for distances << speed of light), and this should be the case for a superconductor, also.johanfprins wrote:You have an inkling but it is still woolly. So let me hone it a bit: A superconductor is a phase through which a current can flow while the applied electric-field is cancelled everywhere within the superconductor.R=0 implies I(in) = I(out) and V(in) = V(out).
However, it allows one to call a vacuum tube "zero resistivity" and a "superconductor" for the vacuum travel portion, which is somewhat absurd...
A superconductor is a conductor that exhibits no voltage differential across its entirety.
I beg to differ. The concept of a conductor is an important physics idea. I am somewhat out of my depth, but I understand a conductor to be a physical material which current flows through.johanfprins wrote:An "implication of zero resistivity" to which you merely add the word "conductor" can in no ways be a rational argument and does not constitute any physics-logic.Which, of course, merely adds "conductor" to the zero resistivity definition.
Since a superconductor is, by definition, a material in which resistivity is 0, you're just being strange. To say what a resistivity of 0 is, you need to say what resistivity is.johanfprins wrote:I have NOT asked for a model for resistivity: I have asked for a definition of zero resistivity which you could not give me. An "implication" is NOT a "definition".And, of course, the model for resistivity is NOT unknown.
Again, I'm out of my depth. It is clear that there is a definite energy transition at which superconductivity starts. It ALSO is clear that this effect is not evident above a transition temperature; that is, above T(c) the material exhibits a resistivity to any voltage, below T(c) the material will only conduct voltages above the excitation energy, but then it does so without losses.johanfprins wrote:The same happens in a semimetal, but the metal still has a resistivity. How are the electrons excited within a superconductor and why is the energy they gain by being excited not deposited as heat within the superconductor?In the band gap theory, a superconductor is a conductor in which the electrons continue to be excited above the valence energy of the material, and so don't undergo the resistivity mechanism.
As near as I can tell, this is because in that realm, the material is stable enough for quantum effects to dominate.