4 ms·

There have been quite a few papers about LK-99, but the only thing I want to see is whether we observer sudden drop of resistance to zero below the critical tem

There have been quite a few papers about LK-99, but the only thing I want to see is whether we observer sudden drop of resistance to zero below the critical temperature that is well above the room temperature at ambient pressure or not. So far, I haven't seen one.

jacquesm 3y ago
That's not a trivial measurement with a small sample. Typically you measure resistance that small like this: +<-------sample------>- ---------p p-------- The + and - leads send a reference current (using something called a 'current source[1]', a specialist supply that cranks the voltage up and down to maintain a steady current, within some arbitrary range, usually from a few mV to 10's or even 100's of volts) that you pick (not so low that you won't get a voltage, not so high that you exceed the expected maximum current for the cross section that you are measuring) down the two leads to the sample and then you measure the voltage across the two points 'p' using the other two leads. This is similar to using a shunt for measuring a current, only now you are interested in the resistance of 'sample'. It also elegantly rules out accidentally measuring the resistance of the probe wires and has the added advantage that you can measure the voltage almost without drawing a current (though at such low resistance you have to take great care to ensure that your measurement doesn't consume a disproportionally large chunk of the reference current). If 'sample' is a nice fat chunk of material you can expect an accurate result because it will be easy to attach to in a reliable way, you can use a lot of current and the sample is large enough to have a resistance high enough that the voltage you are measuring is well outside of the noise. But for a small sample the resistance is almost always going to be very small and the difference between a few nanovolts and zero are hard to distinguish. So that's why you won't be seeing any conclusive measurements of the real resistance (or zero) until larger samples can be made, long enough to show a sizeable voltage drop or none at all. [1] https://en.wikipedia.org/wiki/Current_source https://en.wikipedia.org/wiki/Current_source
httpz 3y ago
This can take a while. With the current fabrication process, they're only getting a chunk with LK-99 particles sprinkled in. Since nobody yet knows how to fabricate a pure chunk of LK-99, it'll be hard to measure the true resistance of LK-99.

jacquesm 3y ago

That's not a trivial measurement with a small sample. Typically you measure resistance that small like this: +<-------sample------>- ---------p p-------- The + and - leads send a reference current (using something called a 'current source[1]', a specialist supply that cranks the voltage up and down to maintain a steady current, within some arbitrary range, usually from a few mV to 10's or even 100's of volts) that you pick (not so low that you won't get a voltage, not so high that you exceed the expected maximum current for the cross section that you are measuring) down the two leads to the sample and then you measure the voltage across the two points 'p' using the other two leads. This is similar to using a shunt for measuring a current, only now you are interested in the resistance of 'sample'. It also elegantly rules out accidentally measuring the resistance of the probe wires and has the added advantage that you can measure the voltage almost without drawing a current (though at such low resistance you have to take great care to ensure that your measurement doesn't consume a disproportionally large chunk of the reference current). If 'sample' is a nice fat chunk of material you can expect an accurate result because it will be easy to attach to in a reliable way, you can use a lot of current and the sample is large enough to have a resistance high enough that the voltage you are measuring is well outside of the noise. But for a small sample the resistance is almost always going to be very small and the difference between a few nanovolts and zero are hard to distinguish. So that's why you won't be seeing any conclusive measurements of the real resistance (or zero) until larger samples can be made, long enough to show a sizeable voltage drop or none at all. [1] https://en.wikipedia.org/wiki/Current_source https://en.wikipedia.org/wiki/Current_source

httpz 3y ago

This can take a while. With the current fabrication process, they're only getting a chunk with LK-99 particles sprinkled in. Since nobody yet knows how to fabricate a pure chunk of LK-99, it'll be hard to measure the true resistance of LK-99.