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coolgod

coolgod

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I don't get the excessive hype of this LK-99 on twitter or Chinese social media, wacky papers are a dime a dozen on the internet. The aphorism extraordinary claims require extraordinary evidence fits well here, no evidence of the sort was presented in the original two papers on Arxiv.

latenlazy said:
Second, since this doesn’t seem to be a type II superconductor, it may not be usable as a superconducting magnet because the superconducting state might get disrupted by strong magnetic fields.
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Even if LK-99 is indeed some sort of exotic superconducting material at room temperature ambient pressure which has no practical uses, the authors of those papers would get very famous since they made a breakthrough in superconductivity in both theory and experimental, very Nobel worthy.

Also this discussion should probably move to Science thread, all the LK-99 discussion is tainting China's actually scientific achievements.

Science Thread

Discuss general scientific developments here. (Some may be related to Sino Defence.) I'll start: https://phys.org/news/2020-04-laws-nature-downright-weird-constant.html New findings suggest laws of nature 'downright weird,' not as constant as previously thought In a paper published in Science...
www.sinodefenceforum.com
 
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Sincho

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The thing is if this discovery of a room temperature superconductor is borne out and we can know the mechanism that underpins the existence of this room temperature superconductivity, we can look into other materials that possess this mechanism but carry better features eg can carry bigger current.
 
sunnymaxi

sunnymaxi

Major
Registered Member
interesting ..

https://twitter.com/i/web/status/1686799780830420992

Researchers at the Department of Physics, Southeast University, Nanjing have synthesized the LK-99 superconductor and have measured 0 resistance until 110 Kelvin and confirmed structural consistency with xray diffraction.


Image
 
coolgod

coolgod

Colonel
Registered Member
sunnymaxi said:
interesting ..

https://twitter.com/i/web/status/1686799780830420992

Researchers at the Department of Physics, Southeast University, Nanjing have synthesized the LK-99 superconductor and have measured 0 resistance until 110 Kelvin and confirmed structural consistency with xray diffraction.


Image
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I couldn't find the paper on arXiv, but I have my doubts about it due to the small irregularly shaped sample, this may not be a bulk superconducting effect. Looking at spacebattle forums recommended here, they claim only 1/6 samples exhibited this behaviour, no Meissner effect observed, and the "zero" resistance is likely due to measurement limitations. The observed "zero" resistance is actually inline with that of a similar sized solid copper conductor at 100K. I would call this a nothing burger, probably explains why I can't find this preprint online.
 
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azn_cyniq

Junior Member
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sunnymaxi said:
interesting ..

https://twitter.com/i/web/status/1686799780830420992

Researchers at the Department of Physics, Southeast University, Nanjing have synthesized the LK-99 superconductor and have measured 0 resistance until 110 Kelvin and confirmed structural consistency with xray diffraction.


Image
Click to expand...
I apologize for bursting this balloon, but they did not actually see "zero resistance." They got 10E-5 Ohms, which is close to the resistance of a similarly-shaped piece of copper (not particularly low). 10E-5 Ohms appears to be the lowest resistance their apparatus can measure. They will need much more sophisticated equipment to actually see zero resistance if LK-99 is actually a superconductor.
 
FairAndUnbiased

FairAndUnbiased

Brigadier
Registered Member
coolgod said:
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I couldn't find the paper on arXiv, but I have my doubts about it due to the small irregularly shaped sample, this may not be a bulk superconducting effect. Looking at spacebattle forums recommended here, they claim only 1/6 samples exhibited this behaviour, no Meissner effect observed, and the "zero" resistance is likely due to measurement limitations. The observed "zero" resistance is actually inline with that of a similar sized solid copper conductor at 100K. I would call this a nothing burger, probably explains why I can't find this preprint online.
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this is still a useful result. decreasing resistance with temperature shows it is a metallic conductor in the normal state. if it was a semiconductor or insulator in the normal state, it would have a filled valence band and empty valence band. the charge carriers would then only be 1. thermally excited electrons and 2. introduced free electrons/holes via doping. Lowering temperature in such a material reduces thermally excited electrons, reducing carrier density, thus increasing resistance.

the shape of the resistance vs temperature curve is interesting. it looks more similar to a superconductor than the metal curve.

Temperature-dependence-of-resistance-of-a-normal-metal-conductor-and-a-superconductor.png

this still doesn't mean its a superconductor. the biggest question is the magnetic phase transition. there should be some decline in the critical temperature as field increases, especially as the original paper claimed only a 300 mA critical current.

We can only say that there is an observable thermal phase transition resulting in resistance change in a metallic material at 100 K. We cannot call it a superconductor yet, because it has not shown a magnetic phase transition. Lack of magnetic phase transition is the most distinguishing feature of a normal metal.
 
coolgod

coolgod

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FairAndUnbiased said:
this is still a useful result. decreasing resistance with temperature shows it is a metallic conductor in the normal state. if it was a semiconductor or insulator in the normal state, it would have a filled valence band and empty valence band. the charge carriers would then only be 1. thermally excited electrons and 2. introduced free electrons/holes via doping. Lowering temperature in such a material reduces thermally excited electrons, reducing carrier density, thus increasing resistance.

the shape of the resistance vs temperature curve is interesting. it looks more similar to a superconductor than the metal curve.

Temperature-dependence-of-resistance-of-a-normal-metal-conductor-and-a-superconductor.png

this still doesn't mean its a superconductor. the biggest question is the magnetic phase transition. there should be some decline in the critical temperature as field increases, especially as the original paper claimed only a 300 mA critical current.

We can only say that there is an observable thermal phase transition resulting in resistance change in a metallic material at 100 K. We cannot call it a superconductor yet, because it has not shown a magnetic phase transition. Lack of magnetic phase transition is the most distinguishing feature of a normal metal.
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Where did you observe the (thermal) phase transition? I don't see any phase transition at all, the resistance values at or below 1E-5, i.e., less than 110K are all inaccurate as it is the lower limit of their measurement apparatus. First, this resistance value at 1E-5 was only observed on 1/6 samples, second even on the observed "zero resistance" sample no Meissner effect was observed.

The blip from 230K-250K is likely due to the electrical contacts thermal expansion?

1691037280360.jpeg
Look at the sample, it is within that tiny triangular piece, so the actual sample is on the order of hundreds of microns or milimeters? Those 4 copper lines within the triangular shaped material is probably the electrical contact points. One poorly attached electrical contact can probably explain these results.
 
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FairAndUnbiased

FairAndUnbiased

Brigadier
Registered Member
coolgod said:
Where did you observe the (thermal) phase transition? I don't see any phase transition at all, the resistance values at or below 1E-5, i.e., less than 110K are all inaccurate as it is the lower limit of their measurement apparatus. First, this resistance value at 1E-5 was only observed on 1/6 samples, second even on the observed "zero resistance" sample no Meissner effect was observed.

The blip from 230K-250K is likely due to the electrical contacts thermal expansion?

View attachment 116734
Look at the sample, it is within that tiny triangular piece, so the actual sample is on the order of hundreds of microns or milimeters? Those 4 copper lines within the triangular shaped material is probably the electrical contact points. One poorly attached electrical contact can probably explain these results.
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Looks to me like there's a slope discontinuity in R vs. T at ~120 K. That could indicate a 2nd order phase transition where R(T) is continuous but dR/dT is not.

I don't know if R(T) is smooth and continuous below 100 K though since 1E-5 is the limit of their precision. So you are correct - I cannot know if there's a 1st order phase transition there.

I'd hope that they know how to take a blank though i.e. putting the exact same Cu contacts on a known pure metal substrate that is definitely not a superconductor, like Cu, Fe or Al.
 
Quickie

Quickie

Colonel
FairAndUnbiased said:
Looks to me like there's a slope discontinuity in R vs. T at ~120 K. That could indicate a 2nd order phase transition where R(T) is continuous but dR/dT is not.

I don't know if R(T) is smooth and continuous below 100 K though since 1E-5 is the limit of their precision. So you are correct - I cannot know if there's a 1st order phase transition there.

I'd hope that they know how to take a blank though i.e. putting the exact same Cu contacts on a known pure metal substrate that is definitely not a superconductor, like Cu, Fe or Al.
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Right after 110 K, the R(ohm) data points jump randomly between 1E-5 and 1E-7.

I very much doubt that this is due to the accuracy of the instrumentation (rather than the actual change in data points), for which the change should be very gradual as the accuracy reduces down the scale.

That is to say, the randomness should increase slowly from 110 K toward the lower temperature if this is anything to do with the limitation of the instrumentation in measuring the smaller values, rather than the sudden jump to the datapoint randomness right after 110 K shown in the graphs, which is something interesting deserving to be looked into further possibly with better equipment.
 
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