3 ms·

Novice question - does a material behaving as a superconductor occur all the sudden like a step function if resistance is plotted against temp and pressure - or

Novice question - does a material behaving as a superconductor occur all the sudden like a step function if resistance is plotted against temp and pressure - or does it ease into super conductor behavior? (edit) Also is it resistance (aka if I remember my EE degree correctly), DC only or also impedance where frequency also matters?

weard_beard 3y ago
all at once. It instantaneously expels the magnetic field. You can observe experiments on youtube: https://www.youtube.com/watch?v=RS7gyZJg5nc#t=32m30s https://www.youtube.com/watch?v=RS7gyZJg5nc#t=32m30s
- 4ad 3y ago
  Only type-I superconductors expel significant magnetic fields. Virtually everything you see on YouTube is a type-II superconductor. type-I superconductors require liquid helium. Also, only type-II superconductors can hover in a stable configuration near magnets. Flux pinning is required for that.
consilient 3y ago
> (edit) Also is it resistance (aka if I remember my EE degree correctly), DC only or also impedance where frequency also matters? Just resistance. Impedance in an ideal BCS superconductor goes roughly as the square of the AC frequency.
sema2 3y ago
I do find that interesting... I found a graph of another HTSC's (YBCO) resistance vs temperature [1], and the function is much more discontinuous looking than the one shown in the article. That would lead me (someone not at all trained in the physics of superconductors) to believe that perhaps the purity of the sample is a factor here, with different parts of the sample having different critical temperatures, gradually decreasing resistance until an inflection point is reached at 110K. 1. https://www.researchgate.net/figure/The-electrical-resistivity-vs-temperature-curve-of-pure-YBCO_fig5_241713900 https://www.researchgate.net/figure/The-electrical-resistivi...
- deleted 3y ago
  [deleted]
- floxy 3y ago
  The ResearchGate chart has a linearly scaled y-axis, the Southeast University chart has a logarithmic scaled y-axis.
marcosdumay 3y ago
It's like freezing water. It happens at a single temperature. It doesn't happen at once, there is a small amount of heat you must take from the material before it becomes a superconductor. Regions of it become superconductors on the process, and those grow until the entire material change. After the change, it becomes a stronger (yes, there is such a thing) superconductor the cooler it gets. (Or, at least that's what happens to the kinds I know about. The thing is complex enough that I wouldn't be too surprised to learn about one that behaves differently.)
- _0ffh 3y ago
  >After the change, it becomes a stronger (yes, there is such a thing) superconductor the cooler it gets Do you mean the tradeoff between temperature, field strength and current? Like, if you lower the temperature, the SC will be able to handle a stronger field or more current in return?
  - marcosdumay 3y ago
    Yes.

weard_beard 3y ago

all at once. It instantaneously expels the magnetic field. You can observe experiments on youtube: https://www.youtube.com/watch?v=RS7gyZJg5nc#t=32m30s https://www.youtube.com/watch?v=RS7gyZJg5nc#t=32m30s

4ad 3y ago
Only type-I superconductors expel significant magnetic fields. Virtually everything you see on YouTube is a type-II superconductor. type-I superconductors require liquid helium. Also, only type-II superconductors can hover in a stable configuration near magnets. Flux pinning is required for that.

consilient 3y ago

> (edit) Also is it resistance (aka if I remember my EE degree correctly), DC only or also impedance where frequency also matters? Just resistance. Impedance in an ideal BCS superconductor goes roughly as the square of the AC frequency.

sema2 3y ago

I do find that interesting... I found a graph of another HTSC's (YBCO) resistance vs temperature [1], and the function is much more discontinuous looking than the one shown in the article. That would lead me (someone not at all trained in the physics of superconductors) to believe that perhaps the purity of the sample is a factor here, with different parts of the sample having different critical temperatures, gradually decreasing resistance until an inflection point is reached at 110K. 1. https://www.researchgate.net/figure/The-electrical-resistivity-vs-temperature-curve-of-pure-YBCO_fig5_241713900 https://www.researchgate.net/figure/The-electrical-resistivi...

deleted 3y ago
[deleted]
floxy 3y ago
The ResearchGate chart has a linearly scaled y-axis, the Southeast University chart has a logarithmic scaled y-axis.

marcosdumay 3y ago

It's like freezing water. It happens at a single temperature. It doesn't happen at once, there is a small amount of heat you must take from the material before it becomes a superconductor. Regions of it become superconductors on the process, and those grow until the entire material change. After the change, it becomes a stronger (yes, there is such a thing) superconductor the cooler it gets. (Or, at least that's what happens to the kinds I know about. The thing is complex enough that I wouldn't be too surprised to learn about one that behaves differently.)

_0ffh 3y ago
>After the change, it becomes a stronger (yes, there is such a thing) superconductor the cooler it gets Do you mean the tradeoff between temperature, field strength and current? Like, if you lower the temperature, the SC will be able to handle a stronger field or more current in return?
- marcosdumay 3y ago
  Yes.