My background: educated amateur. I can design simple to not-quite-simple analog circuits and have taken ordinary but fiddly material property measurements with electronics test equipment and gotten industrially-useful results.
One person alleges an online rumor that poorly connected electrical leads can produce the same graph. Is that a conventional view?
I’m not seeing it. With a bad enough setup, poor technique can do almost anything. I’m not seeing the authors as that awful, though. I don’t think they’re immune from mistakes, but I give low odds on the arbitrarily-awful end of mistakes.
You can model electrical mistakes as some mix of resistors and switches. Fiddly loose contacts are switches, actuated by forces. Those can be magnetic, thermal expansion, unknown gremlins, etc. So “critical magnetic field” could be “magnetic field adequate to move the thing”. Ditto temperature. But managing both problems at the same time in a way that looks like a plausible superconductor critical curve is… weird. The gremlins could be anything, but gremlins highly correlated with interesting properties demand explanation.
Materials with grains can have conducting and not-conducting regions. Those would likely have different thermal expansion behaviors. Complex oxides with grain boundaries are ripe for diode-like behavior. So you could have a fairly complex circuit with fairly complex temperature dependence.
I think this piece basically comes down to two things:
Can you get this level of complex behavior out of a simple model? One curve I’d believe, but the multiple curves with the relationship between temperature and critical current don’t seem right. The level of mistake to produce this seems complicated, with very low base rate.
Did they manage to demonstrate resistivity low enough to rule out simple conduction in the zero-voltage regime? (For example, lower resistivity than copper by an order of magnitude.) The papers are remarkably short on details to this effect. They claim yes, but details are hard to come by. (Copper has resistivity ~ 1.7e-6 ohm*cm, they claim < 10^-10 in the 3-author paper for the thin-film sample, but details are in short supply.) Four point probe technique to measure the resistivity of copper in a bulk sample is remarkably challenging. You measure the resistivity of copper with thin films or long thin wires if you want good data. I’d love to see more here.
If the noise floor doesn’t rule out copper, you can get the curves with adequately well chosen thermal and magnetic switches from loose contacts. But there are enough graphs that those errors have to be remarkably precisely targeted, if the graphs aren’t fraud.
Another thing I’d love to see on this front: multiple graphs of the same sort from the same sample (take it apart and put it back together), from different locations on the sample, from multiple samples. Bad measurement setups don’t repeat cleanly.
My question for the NO side: what does the schematic of the bad measurement look like? Where do you put the diodes? How do you manage the sharp transition out of the zero-resistance regime without arbitrarily-fine-tuned switches?
Do any other results from the 6-person or journal-submitted LK papers stand out as having the property, “This is either superconductivity or fraud?”
The field-cooled vs zero-field-cooled magnetization graph (1d in the 3-author paper, 4a in the 6-author paper). I’m far less confident in this than the above; I understand the physics much less well. I mostly mention it because it seems under-discussed from what I’ve seen on twitter and such. This is an extremely specific form of thermal/magnetic hysteresis that I don’t know of an alternate explanation for. I suspect this says more about my ignorance than anything else, but I’m surprised I haven’t seen a proposed explanation from the NO camp.
My background: educated amateur. I can design simple to not-quite-simple analog circuits and have taken ordinary but fiddly material property measurements with electronics test equipment and gotten industrially-useful results.
I’m not seeing it. With a bad enough setup, poor technique can do almost anything. I’m not seeing the authors as that awful, though. I don’t think they’re immune from mistakes, but I give low odds on the arbitrarily-awful end of mistakes.
You can model electrical mistakes as some mix of resistors and switches. Fiddly loose contacts are switches, actuated by forces. Those can be magnetic, thermal expansion, unknown gremlins, etc. So “critical magnetic field” could be “magnetic field adequate to move the thing”. Ditto temperature. But managing both problems at the same time in a way that looks like a plausible superconductor critical curve is… weird. The gremlins could be anything, but gremlins highly correlated with interesting properties demand explanation.
Materials with grains can have conducting and not-conducting regions. Those would likely have different thermal expansion behaviors. Complex oxides with grain boundaries are ripe for diode-like behavior. So you could have a fairly complex circuit with fairly complex temperature dependence.
I think this piece basically comes down to two things:
Can you get this level of complex behavior out of a simple model? One curve I’d believe, but the multiple curves with the relationship between temperature and critical current don’t seem right. The level of mistake to produce this seems complicated, with very low base rate.
Did they manage to demonstrate resistivity low enough to rule out simple conduction in the zero-voltage regime? (For example, lower resistivity than copper by an order of magnitude.) The papers are remarkably short on details to this effect. They claim yes, but details are hard to come by. (Copper has resistivity ~ 1.7e-6 ohm*cm, they claim < 10^-10 in the 3-author paper for the thin-film sample, but details are in short supply.) Four point probe technique to measure the resistivity of copper in a bulk sample is remarkably challenging. You measure the resistivity of copper with thin films or long thin wires if you want good data. I’d love to see more here.
If the noise floor doesn’t rule out copper, you can get the curves with adequately well chosen thermal and magnetic switches from loose contacts. But there are enough graphs that those errors have to be remarkably precisely targeted, if the graphs aren’t fraud.
Another thing I’d love to see on this front: multiple graphs of the same sort from the same sample (take it apart and put it back together), from different locations on the sample, from multiple samples. Bad measurement setups don’t repeat cleanly.
My question for the NO side: what does the schematic of the bad measurement look like? Where do you put the diodes? How do you manage the sharp transition out of the zero-resistance regime without arbitrarily-fine-tuned switches?
The field-cooled vs zero-field-cooled magnetization graph (1d in the 3-author paper, 4a in the 6-author paper). I’m far less confident in this than the above; I understand the physics much less well. I mostly mention it because it seems under-discussed from what I’ve seen on twitter and such. This is an extremely specific form of thermal/magnetic hysteresis that I don’t know of an alternate explanation for. I suspect this says more about my ignorance than anything else, but I’m surprised I haven’t seen a proposed explanation from the NO camp.