One of the common threads seems to be that other scientists think that lk-99 is not a super conductor but just strongly diamagnetic.
As a non physicist i wonder if that is useful in and of itself? Skimming wikipedia it doesn't seem like there are that many strongly diamagnetic materials. Would discovering a new one still be a big discovery (just not earth shattering)
That depends on how the diamagnetism comes about. One way in which it could come about which would still make it a big discovery is if the material is locally superconducting but not globally. That would give you diamagnetism without superconductivity on a usable scale and might in turn open the door to modifying the material to increase the size of the superconducting regions. Pure speculation, obviously, the bigger chance is that if the material is 'just' diamagnetic that it is simply diamagnetic in the same way in which other materials are (all particles of which the samples are made are constructed such that all electrons are paired).
My understanding is that taking the paper at face value it seems like they’re saying the diamagnetism was an encouraging piece of supporting evidence beyond their other rationale for what they believe they’ve found. I’m not enough of a physicist (or one at all) to speak to that though so I guess I’ll just sit here wit ma popcorn for the next week with everyone else
I see. V=IR=0 means R can measure as 0, but they did measure small current. Presumably they know the voltage. That seems odd if they can’t measure the resistance accurately if their instrumentation is rated to measure that current.
It is not possible to determine that a resistance is exactly zero through direct measurement, because any kind of probes that can be used to contact the material will have a high contact resistance, which will vary from one probe contact to another.
Even when the resistance is measured with a 4-point probe, the only conclusion that can be reached is that the resistance is smaller than the experimental error.
However it should be possible to determine that the resistance is zero through various indirect effects, for instance by establishing a closed current in the material and verifying that it does not decrease in time.
Even such experiments must be done carefully because some materials with unusual magnetic properties may behave apparently in a similar way to superconductors in some experiments, e.g. both a magnetized ferromagnetic material and a superconductor ring carrying a current will have a remanent magnetic field that is constant in time and in both cases the magnetic field will disappear when the temperature is raised above a threshold.
Thanks that’s interesting. If it’s so hard to determine if a substance is superconducting, does that mean many substances that are apparently but not quite superconducting have similar applicability? I.e., if you need superconductors for X application, can you not just put the substance in question in that application and observe if it works or not? Sorry for the dumb questions.
As a non physicist i wonder if that is useful in and of itself? Skimming wikipedia it doesn't seem like there are that many strongly diamagnetic materials. Would discovering a new one still be a big discovery (just not earth shattering)