Separating Real Superconductivity from Similar to Superconducting

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Professor Michael Fuhrer of Monash University explains the challenges to definitively prove superconductivity.

You’d think superconductivity would be easy to detect; it comes with zero electrical resistance, so if you measure resistance, and it’s zero, you’re done. Unfortunately there are many ways to get fooled.

Generally you’ll see multiple pieces of evidence for superconductivity in a new report: Meissner effect, AC susceptibility, temperature-dependent critical field and critical current, single-particle tunneling gap, jump in specific heat at T_c, Josephson tunnelling, AC Josephson effect, etc. (Probably not all of these in one paper, but usually at least a couple in addition to zero resistance.

There is a steady trickle of difficult-to-explain results that look a lot like superconductivity, sometimes at unexpectedly high temperatures. “Tantalizing” is often used.

6 thoughts on “Separating Real Superconductivity from Similar to Superconducting”

  2. The superconducting state and normal state of a substance are separate thermodynamic phases, analogous to the gas, liquid, and solid phases of a substance, with H (magnetic field strength) and M (magnetization or the level of field penetration into the material) being the relevant thermodynamic parameters instead of P (pressure) and V (volume). Does the material exhibit two critical magnetic fields – H1 and H2 – where there is partial penetration of the field into the material for an applied external field H where H1< H H2? This is a required property for any superconductor that exhibits zero resistance at temperatures that are not near zero degrees Kelvin, i.e. Type II superconductors.

  3. Hi Brett,

    I think you said this a few more places in comments. That said (pun intended) that would work if it is omnidirectional. For a unidirectional superconductivity (which would definitely be something new, but has been hinted at in modeling) I don’t think that would work. Maybe LK-99 isn’t a superconductor but just has some strange properties. Maybe it is but a new “type” with unidirectional superconductivity. I don’t think it was an intentional fraud; there is definitely something odd about this material. It is encouraging that other labs are starting to synthesize samples. Time will tell.

  4. The most straightforward test, though difficult to perform with tiny samples, is to just create a loop, and induce a persistent current. For such a current to last more than a few seconds requires effectively zero resistance, to a precision hard to measure otherwise.

    • Hi Brett,

      I think you said this a few more places in comments. That said (pun intended) that would work if it is omnidirectional. For a unidirectional superconductivity (which would definitely be something new, but has been hinted at in modeling) I don’t think that would work. Maybe LK-99 isn’t a superconductor but just has some strange properties. Maybe it is but a new “type” with unidirectional superconductivity. I don’t think it was an intentional fraud; there is definitely something odd about this material. It is encouraging that other labs are starting to synthesize samples. Time will tell.

    • My intuition about superconductivity, because it’s facilitated by low heat or extreme pressure, is that resistance as a property of molecular structure is dependent on geometry. That’s what makes LK99 so “tantalizing”. Zero resistance by geometry alone. I think, if it does superconduct, there might be limitations on creating this loop you describe.

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