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> The Bath researchers conclude that while superconductivity is considerably weakened by the magnetic effect, it is not fully destroyed. I'm a bit confused by

> The Bath researchers conclude that while superconductivity is considerably weakened by the magnetic effect, it is not fully destroyed. I'm a bit confused by this, I thought that superconductivity is a 'yes or no' property, but here it is 'weakened', what does it mean in this context ? Is it that the material is either superconductor or magnetic, but not both at the same time and place, and that it can be reversed ?

adrianN 5y ago
Superconductivity is a phase change phenomenon so it is often characterized as binary, but, as I understand it, superconducting materials have properties like the maximum amount of current they tolerate before superconductivity breaks down that allow you to compare different materials as "more" or "less" superconducting.
magicalhippo 5y ago
Not an expert, but it seems the material they're talking about is a Type-2 superconductor[1], which has a more gradual transition in the presence of magnetic fields. [1]: https://en.wikipedia.org/wiki/Type-II_superconductor https://en.wikipedia.org/wiki/Type-II_superconductor
patrakov 5y ago
Superconductivity is not really a "yes or no" property. It can be destroyed by a too-strong external magnetic field, or, equivalently, a too-strong current. The quantitative side of this thing (i.e. what allows us to say "superconductivity is weakened") is "how strong is too-strong". We can also talk about the "order parameter", which is related to the fraction of conductivity electrons participating in Cooper pairs, and to the depth (usually ~100 nm) to which the external magnetic field does penetrate the superconductor. The arXiv link to the original research is https://arxiv.org/abs/2010.09901v2 https://arxiv.org/abs/2010.09901v2, and from Fig. 1, it follows that they are talking about a Type II superconductor, which does allow some magnetic field to pass through the bulk of it, in the form of vortices. Obviously, the volume occupied by the vortices is not superconductive, but they are shunted by the remaining bulk of the material, and therefore the resistance of the whole specimen is still zero.
- raziel2701 5y ago
  If a material is in the superconductive state it does not coexist with a non-conductive or regular conductive phase, all of the material is superconductive. In that sense, it is a "yes or no" property. What you're talking about is applying a magnetic field, which I'd argue is you're doing something to fuck with it, but if we're talking just lower the temperature and check its resistivity, then superconductivity is a yes or no state.
  - willis936 5y ago
    All of the material (that is below the critical temperature, critical current, and has no magnetic field penetrating it). Which is to say not all of the material. It is common to have pockets of non-superconducting material in superconductors. If they get too big in the wrong places then you quench. Applied magnetic fields are common because, unsurprisingly, superconductors often find themselves used to make large magnetic fields without having to pay the electric company or cooling ohmic losses. Some applications can get by with just one magnet. Many others cannot.
    - raziel2701 5y ago
      Having pockets of material being non-superconductive means they're a different phase (like crystallographic or stoichiometrically), that is a defect. I'm talking about a material that doesn't have any kind of phase segregation. In that case, the superconductive phase it 100% a "yes or no" property and that's that. You're wrong.
raziel2701 5y ago
The "weaker" part refers to how susceptible the state is to a magnetic field. A high enough magnetic field will remove the superconducting state, and this material is on the lower side of magnetic field threshold. Superconductivity is generally a "yes or no" property like you said, there's no phase coexistence within the material of a superconductive and regular conductor phase (unless an applied magnetic field is present, in which case there is latent heat).

adrianN 5y ago

Superconductivity is a phase change phenomenon so it is often characterized as binary, but, as I understand it, superconducting materials have properties like the maximum amount of current they tolerate before superconductivity breaks down that allow you to compare different materials as "more" or "less" superconducting.

magicalhippo 5y ago

Not an expert, but it seems the material they're talking about is a Type-2 superconductor[1], which has a more gradual transition in the presence of magnetic fields. [1]: https://en.wikipedia.org/wiki/Type-II_superconductor https://en.wikipedia.org/wiki/Type-II_superconductor

patrakov 5y ago

Superconductivity is not really a "yes or no" property. It can be destroyed by a too-strong external magnetic field, or, equivalently, a too-strong current. The quantitative side of this thing (i.e. what allows us to say "superconductivity is weakened") is "how strong is too-strong". We can also talk about the "order parameter", which is related to the fraction of conductivity electrons participating in Cooper pairs, and to the depth (usually ~100 nm) to which the external magnetic field does penetrate the superconductor. The arXiv link to the original research is https://arxiv.org/abs/2010.09901v2 https://arxiv.org/abs/2010.09901v2, and from Fig. 1, it follows that they are talking about a Type II superconductor, which does allow some magnetic field to pass through the bulk of it, in the form of vortices. Obviously, the volume occupied by the vortices is not superconductive, but they are shunted by the remaining bulk of the material, and therefore the resistance of the whole specimen is still zero.

raziel2701 5y ago
If a material is in the superconductive state it does not coexist with a non-conductive or regular conductive phase, all of the material is superconductive. In that sense, it is a "yes or no" property. What you're talking about is applying a magnetic field, which I'd argue is you're doing something to fuck with it, but if we're talking just lower the temperature and check its resistivity, then superconductivity is a yes or no state.
- willis936 5y ago
  All of the material (that is below the critical temperature, critical current, and has no magnetic field penetrating it). Which is to say not all of the material. It is common to have pockets of non-superconducting material in superconductors. If they get too big in the wrong places then you quench. Applied magnetic fields are common because, unsurprisingly, superconductors often find themselves used to make large magnetic fields without having to pay the electric company or cooling ohmic losses. Some applications can get by with just one magnet. Many others cannot.
  - raziel2701 5y ago
    Having pockets of material being non-superconductive means they're a different phase (like crystallographic or stoichiometrically), that is a defect. I'm talking about a material that doesn't have any kind of phase segregation. In that case, the superconductive phase it 100% a "yes or no" property and that's that. You're wrong.

raziel2701 5y ago

The "weaker" part refers to how susceptible the state is to a magnetic field. A high enough magnetic field will remove the superconducting state, and this material is on the lower side of magnetic field threshold. Superconductivity is generally a "yes or no" property like you said, there's no phase coexistence within the material of a superconductive and regular conductor phase (unless an applied magnetic field is present, in which case there is latent heat).