Can you tell us more about why it is an interesting property?
hinkley 8 days ago [-]
From the article:
> The -233°C threshold (40 K), often associated with the McMillan limit, marks a boundary beyond which conventional superconductivity theories become less predictive.
So it’s like finding a gas giant exoplanet that’s in the “wrong” place. We understand Jupiter and Saturn. We don’t understand a gas giant orbiting its star in ten days. Thats weird. And science can’t progress when there is nothing “weird”. It means all the data matches our models. It’s boring. It has nothing to teach.
A ten day orbit or a normal metal group superconductor are outside our comfort zone and may mean new physics.
We have two classes now, copper and iron based superconductors that work at room temperature above 40K or so. Below 40K, there are countless superconductors and the mechanism they use breaks down at around 40K. There's no reason to think that a material which is a superconductor below 40K will have some variant that is one above 40K.
Once we have evidence of superconductivity above 40K or so (at normal pressures) things change. Those materials follow different rules that we only partially understand. And there is reason to hope that variants exist which will be superconductors at even higher temperatures. There's no set barrier or upper limit once you cross the 40K threshold. One may exist, but we don't know it.
What happened with copper, and iron (to a much lesser extent), is that we marched up the curve and eventually made superconductors with many real-world. Once you reach 77K (-195C) we're in business. The hope is that maybe we can do the same with nickel. This has traditionally only really worked well with copper-based compounds.
Having a 3rd class of materials gives us a lot more options. And the more examples we have, the more likely we are to come up with some useful theory.
p1mrx 8 days ago [-]
If we're trying to understand how superconductors work, then it's useful to have more examples.
mort96 8 days ago [-]
Yes that makes sense, but why is Nickel specifically interesting?
msandford 8 days ago [-]
Nickel itself isn't interesting. Any new material is interesting. Yet another YbCo-whatever wouldn't tell you as much as an entirely new metal. It would be just as interesting if it was titanium or vanadium or lithium or any other metal that hasn't ever been found in a superconductor before.
creddit 8 days ago [-]
Because it may lead to new classes of high temperature ambient pressure superconductors. Maybe even leading to room temperature + pressure superconductors.
gsf_emergency_2 8 days ago [-]
a recent work claims that
in principle the upper bound to the critical temp of conventional sc at ambient p is ~100K, so this is a valid empirical step in that direction
If you are wondering why this matters: It's not for a commercial product, it's to help understand why some materials superconduct.
boothby 8 days ago [-]
Hot* take: -233 is too cold for Celsius. I'm okay with folks reporting critical temperatures in C once they get near room temperature, but this is only 40K (which is blazingly hot in my world, but regardless).
But, it's cool to see the boundaries pushed on the McMillan limit, and that figure with a lazy Susan of sputtering targets looks fun.
* pun acknowledged
loufe 8 days ago [-]
I'm curious by what measure you suggest it's "too cold". Kelvin is an offset celsuis, so it's not like we're talking about an innapropriate order (like 10 000 000 grams vs. 10 tonnes).
I would understand if it detracted from one's understanding, but I think this format is more accessible than assuming everyone knows what kelvin are, and it's explained in the first sentence. This is journalism, accessibility to science should be lauded while maintaining brevity for , IMO.
hexaga 8 days ago [-]
Frame of reference. Kelvin immediately tells you the distance from absolute zero, which is at least somewhat relevant in this context. Celsius tells you the distance from liquid water which isn't very helpful in understanding the figure.
I think fewer people know the offset between K and C than the fact that 0K represents absolute zero.
jayyhu 8 days ago [-]
For the layman, 0 degrees celsius is also a good proxy for the distance to "room temperature" superconductor.
rzzzt 8 days ago [-]
-196℃ is another point of reference that might be familiar to people interested in, ehm, cold.
smcin 8 days ago [-]
Nitrogen melting point. Essentially the highest low temperature at which you can cheaply do supercold stuff.
smcin 7 days ago [-]
(I meant nitrogen boiling point.)
fooker 8 days ago [-]
There’s another more fundamental reason to use Kelvin here, linearity.
100K is twice as hot as 50K, while the idea of twice as hot is meaningless in C or F.
florbnit 7 days ago [-]
Isn’t it the exact opposite? It you talk to people about something being “twice as warm” or “half as warm” people will assume you are talking about a scale in celcius or something closely related? Because it doesn’t make sense to say “the bedroom is freezing it’s 3/100th colder than the living room!” And no one saying “the bedroom is half as warm as the living room” will be interpreted to be saying that it’s -127 degrees celcius.
fooker 7 days ago [-]
No I mean this in a physics sense, not ‘feelings’ sense.
If there is a physical phenomenon that depends on temperature, you can’t use C or F in that calculation unless the temperature parameters somehow cancel out.
So, if y = Tx, twice the temperature means y is twice if x is constant. But only if it’s in Kelvin.
florbnit 6 days ago [-]
In a “physics sense” there is no such thing as warm or cold those are language constructs not physical properties of materials. In physics there is temperature. You don’t say “the metal bar is 20 warm” you say “temperature is 20 degrees celcius” something having “twice the temperature” isn’t the same as being twice as warm or twice as cold.
fooker 5 days ago [-]
I'm not sure if you got the point but I'll repeat. I am not talking about language.
40C is not twice the temperature as 20C, but 40K is twice the temperature as 20K.
florbnit 4 days ago [-]
You are using language and you seem to make an equivalence of temperature to warm/cold which doesn’t work. Now your saying that it only makes sense to use kelvin because it’s the only scale that doubles when you double it (which is actually also false they all do that). When in fact the concept of “twice as warm” is a fuzzy language construct which matches better to celcius. Which isn’t surprising as both the language and celcius scale are designed around our subjective experience.
boothby 8 days ago [-]
> I'm curious by what measure you suggest it's "too cold".
I'm accustomed to thinking about superconductors in an environment on the order of around ~0.01K. And, it's worth spending a little time understanding absolute temperature. Take, say, Zirconium -- its critical temperature is around 0.55K. This new material's Tc is around 40/.55 = 73 times hotter. This perspective is useful if you're thinking about how much work it'll be to get something down to a given temperature. So you've kinda hit my complaint on the head -- it's precisely because temperatures of that magnitude don't make sense to me. And I'd expect folks reading phys.org to be unsurprised by temperatures reported in K.
Rendered at 14:57:06 GMT+0000 (Coordinated Universal Time) with Vercel.
https://en.wikipedia.org/wiki/List_of_superconductors -- sort by Tc (K)
> The -233°C threshold (40 K), often associated with the McMillan limit, marks a boundary beyond which conventional superconductivity theories become less predictive.
So it’s like finding a gas giant exoplanet that’s in the “wrong” place. We understand Jupiter and Saturn. We don’t understand a gas giant orbiting its star in ten days. Thats weird. And science can’t progress when there is nothing “weird”. It means all the data matches our models. It’s boring. It has nothing to teach.
A ten day orbit or a normal metal group superconductor are outside our comfort zone and may mean new physics.
We have two classes now, copper and iron based superconductors that work at room temperature above 40K or so. Below 40K, there are countless superconductors and the mechanism they use breaks down at around 40K. There's no reason to think that a material which is a superconductor below 40K will have some variant that is one above 40K.
Once we have evidence of superconductivity above 40K or so (at normal pressures) things change. Those materials follow different rules that we only partially understand. And there is reason to hope that variants exist which will be superconductors at even higher temperatures. There's no set barrier or upper limit once you cross the 40K threshold. One may exist, but we don't know it.
What happened with copper, and iron (to a much lesser extent), is that we marched up the curve and eventually made superconductors with many real-world. Once you reach 77K (-195C) we're in business. The hope is that maybe we can do the same with nickel. This has traditionally only really worked well with copper-based compounds.
Having a 3rd class of materials gives us a lot more options. And the more examples we have, the more likely we are to come up with some useful theory.
https://arxiv.org/abs/2406.08129
The McMillan limit has been challenged before
https://www.nosta.gov.cn/pc/en/awards/prize1/1460.shtml
But, it's cool to see the boundaries pushed on the McMillan limit, and that figure with a lazy Susan of sputtering targets looks fun.
* pun acknowledged
I would understand if it detracted from one's understanding, but I think this format is more accessible than assuming everyone knows what kelvin are, and it's explained in the first sentence. This is journalism, accessibility to science should be lauded while maintaining brevity for , IMO.
I think fewer people know the offset between K and C than the fact that 0K represents absolute zero.
100K is twice as hot as 50K, while the idea of twice as hot is meaningless in C or F.
If there is a physical phenomenon that depends on temperature, you can’t use C or F in that calculation unless the temperature parameters somehow cancel out.
So, if y = Tx, twice the temperature means y is twice if x is constant. But only if it’s in Kelvin.
40C is not twice the temperature as 20C, but 40K is twice the temperature as 20K.
I'm accustomed to thinking about superconductors in an environment on the order of around ~0.01K. And, it's worth spending a little time understanding absolute temperature. Take, say, Zirconium -- its critical temperature is around 0.55K. This new material's Tc is around 40/.55 = 73 times hotter. This perspective is useful if you're thinking about how much work it'll be to get something down to a given temperature. So you've kinda hit my complaint on the head -- it's precisely because temperatures of that magnitude don't make sense to me. And I'd expect folks reading phys.org to be unsurprised by temperatures reported in K.