The interesting thing about this is that the work neatly fitted with existing theory:

> Drozdov et al. observed this isotope effect and found that, compared with the lanthanum hydride samples, the critical temperature in lanthanum deuteride samples is lower by almost exactly the amount predicted by the theory.

So like the article points out:

> From a scientific standpoint, these results suggest that we might be entering a transition from discovering superconductors by empirical rules, intuition or luck to being guided by concrete theoretical predictions.

Whilst this result might require huge pressures, steady progress towards a theory of super-conduction is an exciting thing indeed.

I wouldn't be too optimistic. The theory they are talking about is BCS theory. Most of the other high TC superconductors cannot be explained with it and high TC BCS superconductivity so far requires crazy environments with no clear path to making them easier to use. With the kinds of pressures required to make this happen, it's probably easier to just buy liquid nitrogen and use other materials.

Also it may open the road to find metastable material at room temperature, although I don’t think that it’s the case for lantanium hydride.

At pressures a million times those experienced on earth. Still an advance, of course.

Nobody wants "high temperature" superconductors. They want superconductors at roughly standard temperature and pressure. This is only an advance by the extremely artificial metric of considering temperature only. Ceramic superconductors work at liquid nitrogen temperatures and standard pressure, which is much more accessible.

I'm not raging at ttsda. It is an advance. Of sorts. But not nearly as much as the headline suggests.

You’re vastly underestimating what the significance of what this is part of. High Tc superconductivity was thought to be essentially dead. Extremely few significant new results for decades. Now this and magic angle twisted graphene and some other stuff. It’s really really cool. It’s like we’re watching an entire field thawing and lurching forward.

Is the graphene thing dead? One paper indicated graphene or even graphite soaked in a hydrocarbon would superconduct at room temperature. I was so excited I purhased some and tried that, it had a DC impedance similar to dry graphite...

Did you buy graphene or graphite? If the former, maybe what you got wasn't actually graphene? Apperently, the progress in this field is held back by most suppliers selling something they claim that's graphene but really isn't (or is of garbage quality) - https://blogs.sciencemag.org/pipeline/archives/2018/10/11/gr....

This is addressed in the second to last paragraph:

> The effort to manufacture synthetic diamond provided substantial motivation for the development of high-pressure methods. Today, however, synthetic diamonds are grown using a low-pressure technique called chemical-vapour deposition. Optimistically, it might eventually be possible to use similar low-pressure methods to produce metastable superconducting compounds that are initially discovered at high pressure.

The headline is accurate.

In the scientific community, High-Tc superconductors typically refer to Type II superconductors, eg cuprates. And the “High-Tc” term means above temperatures relative to the usual elemental superconductor Tc’s, eg about 20K or so.

Materials that can superconduct above 77K are especially sought after since they can be cooled with only liquid nitrogen, much cheaper and abundant than liquid helium.

The maximum current and magnetic field you can apply to a supercondutor correlates very well with Tc, and it is likely that they are intrinsically linked so this correlation is unavoidable.

So, no, everybody cares about high temperature superconducors, because the higher the temperature, the strongest magnet you can build out of them.

What's wrong with high pressure superconductors? At least those don't require constant energy input, which would seem to be an improvement.

at a 1E6 atm, it's beyond useless for any practical application (unlike "normal" superconductors that can be used with a bit of N2 plumbing). If you scroll through the paper, you'll see they talk about using a diamond anvil.

Even if we could compress anything other than a spec of this stuff, it would still require massive amounts of PV work to achieve the P required.

I thought "high temperature", when talking about superconductors, basically means any temperature above the boiling point of nitrogen...

I think you may mean below.

Basically, low temperature superconductors (e.g. niobium titanium) are liquid helium cooled.

High temperature superconductors (e.g. YBCO, BSCCO) are everything else, but generally liquid nitrogen cooled.

Also, the temperature (250 K, -23°C) is a bit chilly to be called “room temperature”. Still, this means you don’t need liquid nitrogen for cooling: a good but standard refrigeration system would be enough (and their insane diamond pressure apparatus, of course).

Isn’t nitrogen cooling much easier to achieve than this level of pressure?

well the pressure aspect wouldn't require constant energy input. And I assume it is a lot more economical to use a consumer refrigerator than liquid nitrogen.

But yah, you can bathe a much more complicated "circuit" in liquid nitrogen a lot easier than compressing it with diamond anvils. Though no commercial superconducting computers have emerged, cmos is just too cost effective currently, and the known examples are still in the 4K range.

"well the pressure aspect wouldn't require constant energy input."

But you have to put energy in to compress it, energy that is lost (since you're compressing it isothermally). Since we're talking about 1E6 atm, any appreciable volume would require insane amounts of E to compress.

Wouldn't that also be pretty much a bomb if the pressure got relieved? I don't know how to do the math but 1E6 atm seems a lot of energy (is it potential energy?) that has to go somewhere.

TL;DR: It's pretty much like a bomb, yes.

How much energy it is depends on the volume change as you compress. If your material is completely incompressible, there is no volume change, no work done as the pressure rises, and therefore no energy stored.

In practice, for a material of bulk modulus K by definition you have

  -K dV/V = dP.

as the basic differential equation relating pressure and volume (if we assume that the bulk modulus is constant through our pressure range, which is quite an assumption in this case). Solving that, we get:

  V = V_0/exp(P/K)

where V_0 is the original volume and V is the volume after the pressure has been applied. Bulk modulus is commonly measured in GPa, so we're going to do that here. 1atm is about 1e5 Pa or 1e-4 GPa.

The work done while compressing is the integral of -PdV, which per that first differential equation we can rewrite as the integral of P * V/K * dP (we want to integrate dP because we know what the limits are: it's going from 1atm, or 1e-4 GPa, to 1e6 atm = 1e2 GPa).

Plugging in our expression for V we get the integral, from 1e-4 to 100, of P/K * V_0/exp(P/K) dP. The integral there is:

  K * V_0 * (-P/K - 1) * exp(-P/K)

For simplicity, I'm going to approximate that 1e-4 by 0, so we get:

  K * V_0 * ((-100/K - 1) * exp(-100/K) + 1)

when we evaluate at the two endpoints.

OK, so let's try an actual material and actual volume. Steel has a bulk modulus of 160 GPa according to <https://en.wikipedia.org/wiki/Bulk_modulus#Selected_values>. So for steel we have:

  160 * V_0 * ((-100/160 - 1) * exp(-100/160) + 1) =
  160 * V_0 * 0.13 =
  21 * V_0

or so. If we assume we started with a 1 cm^3 volume of steel, that's an energy of:

  21e9 N/m^2 * 1e-6 m^3 = 2.1e4 J

or about equivalent to 5 grams of TNT per <https://en.wikipedia.org/wiki/TNT_equivalent>. For comparison, 1 cm^3 of steel is about 7-8 grams of material, so we're right in the "about as much energy as the same weight of TNT" ballpark. Obviously if you start with a larger volume you end up with more stored energy: if we started with 1m^3 we end up equivalent to about 5 tons of TNT.

If your material is more compressible, the numbers are higher, as long as it's not too compressible (in which case it just collapses into a tiny volume quickly and not much more work gets done after that). If we take K = 50 (a typical number for glass from that table), you get:

  50 * V_0 * ((-100/50 - 1)*exp(-100/50) + 1) =
  50 * V_0 * 0.6 =
  30 * V_0

If your material is less compressible, you store less energy; for diamond with K = 443, you get something like 9.7*V_0.

Again, all this assumes pressure-invariant bulk modulus, which seems moderately unlikely when you are dealing with pressures that are on the order of the size of the bulk modulus or even larger, as here.

An upvote is not enough. Your comment is the reason I love HN.

It would depend on what happens when the material is removed from the high-pressure environment.

As the article points out, diamonds naturally form in a high-pressure environment but are stable at standard atmosphere and temperature.

I'm not entirely sure but I think there are no theoretical obstructions to maintaining a ridiculously high pressure indefinitely.

Although I suppose there aren't any theoretical obstructions to indefinitely maintaining low temperatures either.

Even blackholes lose their mass through radiation. Nothing can maintain a high pressure indefinitely.

This.

lanthanum hydride @ 250K at > 1 million atm.

It's still very impressive though.

Technically correct. The most annoying kind of correct.

this made me think, is the earth core a superconductor?

No. The core has pressure but it's way too hot to achieve super conductivity.

Interesting idea. It would help to explain persistence of Earth's magnetic field.

> From a scientific standpoint, these results suggest that we might be entering a transition from discovering superconductors by empirical rules, intuition or luck to being guided by concrete theoretical predictions.

That would be an exciting development.

Is the Sun a superconductor? The Sun consist of a high percentage of hydrogen ~73% and there must be really high pressure at the center.

The suns central pressure is 2.5*10^11 bar according to nasa.

https://en.m.wikipedia.org/wiki/Sun

https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

The sun is also at a temperature of millions of degrees. At these temperatures, there is no such thing as chemical bonds, and so the rules with hydrogen from the article don't apply.

interesting, is this a sub-field of physics ? high temperature physics or something ?

Plasma physics I guess, plus magneto hydrodynamics, plus GR for really heavy stars.

dank u

High energy physics, yes.

danke schon

No, it's a plasma. The high pressure in the article is a way of getting to a part of the phase diagram of that particular crystal where the superconducting transition happens at a higher temperature.

How about the metallic hydrogen that might exist at Jupiter's core?

it's probably too hot in there, but I wondered the same thing

Maybe some properties of stars could be explained by superconductivity.

Has this been discussed here? Navy files for patent on room-temperature superconductor.

https://phys.org/news/2019-02-navy-patent-room-temperature-s...

"The application claims that a room-temperature superconductor can be built using a wire with an insulator core and an aluminum PZT (lead zirconate titanate) coating deposited by vacuum evaporation with a thickness of the London penetration depth and polarized after deposition.

An electromagnetic coil is circumferentially positioned around the coating such that when the coil is activated with a pulsed current, a non-linear vibration is induced, enabling room temperature superconductivity.

"This concept enables the transmission of electrical power without any losses and exhibits optimal thermal management (no heat dissipation)," according to the patent document, "which leads to the design and development of novel energy generation and harvesting devices with enormous benefits to civilization.""

> lanthanum hydride compounds become superconducting at 250 K

That's about -10F, or -23C.

(And it would make a lot more sense to put that in the article. Most of us don't "think" in Kelvin.)

It's easy: "room temperature" is about 300K.

That’s regular outdoor temperature in a lot of places. I wonder if there is any type of tech that is used in cold climates (or more on cold days) that would benefit from superconductors so they become more efficient when it’s most needed?

Oh - it has to be at 1atm and -20 of course...

Oh thanks!

Especially since the article says room temperature. I know a lot of people on HN are interested in superconductors but don't necessarily use K frequently if ever.

> Writing in Nature, Drozdov et al.1 report several key results that confirm that, when compressed to pressures of more than one million times Earth’s atmospheric pressure, lanthanum hydride compounds become superconducting at 250 K — a higher temperature than for any other known material.

One million atmospheres is an important detail to leave out of the title.

> "Materials known as superconductors transmit electrical energy with 100% efficiency."

What is the level of (in)efficieny for say power lines? And power cords, etc around the office/house?

That is, of the electricity produced, how much is lost due to how it's transported? Does decentralizing production (e.g., solar panels on your own roof) help in any way?

US grid: losses are 5%. EU grid was in the same ballpark. The wiki page [0] is the source and was pretty much the best summary i could find when i was looking for it a while back. I'd love to read better material about it. Btw, losses seem to include theft. Wonder if much of a thing that still is.

> In general, losses are estimated from the discrepancy between power produced (as reported by power plants) and power sold to the end customers

[0] https://en.wikipedia.org/wiki/Electric_power_transmission#Lo...

wow, that's way better than I would have imagined.

5% loss isn't that bad, but that's because they're being limited in a lot of ways to keep the efficiency high. Dropping current and increasing voltage, for instance. If you had a 100% efficient conductor, you could do things like transmit monstrously high levels of current without having to worry about stuff like that.

True, although the superconducting effect is lost under high electric fields.

A superconducor rejects magnetic fields (a bit like a Faraday cage). What if you cranck it up high enough and force the superconductor in place? You lose superconductivity.

For that reason, there is actually a limit to thew current that can be transmitted, though it is much higher than with conventional cables (you still can't power a city with a hair-thin cable, IIRC).

The bit of heat produced in a power line isn't a huge deal. The more important applications will be in electronics and electromagnets. For instance, it would make nuclear fusion reactors cheaper and easier to build.

Also batteries https://en.wikipedia.org/wiki/Superconducting_magnetic_energ...

So this isn't about advancing scale and distribution, it's at the end product and product sub-component level. Good to know.

It is also possible it will enable some setups that aren't currently possible. Part of why transmission loss in power lines is as low as it is is that we build plants near to where the electricity is going to be used, so it's not some sort of physics law that the loss is that low, it's engineering. Right now, the "plate the Sahara in solar to power Europe" solution is not technically feasible due to the transmission loss across that distance. Obviously that's a special case of the general problem of natural power sources not being where people live. If we can transmit power without loss, we get some more options than we have now.

I'd still guess the bulk of the value would be in more local uses, but there are some interesting large-scale possibilities, including power transmission.

Ya, but the science popularizers always make it about transmission :S

The inefficiency/losses depends on the distance, the voltage, and a few other things. In practice, losses are about 5% in the USA.

https://en.m.wikipedia.org/wiki/Electric_power_transmission#...

Insignificant: EEs can lower the losses by increasing the line voltage [0], at the expense of other challenges (namely taller pylons). It's about 5% over the length of the line.

Consider the other losses:

- Thermal (gas turbine) cycle: 40-60% lost (the big one) - Transformer loss: 1-2%. You pay this every time you step up/down, so it adds up. - Capacitive coupling: I dunno, but length dependent. It has to be about the same as Ohmic losses since once it's large you switch to DC lines (and take an Ohmic loss hit from lower V) - You're house's power factor (which, unlike industrial users, you're not charged for).

[0] in the sixties very large V lines were introduced (0.75 - 1.0 MV ??). They work, but it's not considered worthwhile.

Also, super conductors are limited by the amount of magnetic field, and therefore current they can carry [0] (above that limit they become normal conductors). Lowering T bellow Tc, increasing P increases the amount of current you can carry.

Point is, they're kinda useless for transmission.

[0] MRI magnets are superconducting for the efficiency of superconductors, not for the field strength! The strongest magnets are not made of superconductors but out of copper pipes: electrical conductors with coolant pumped through them!

Smaller than or equal to about 1 percent is fairly normal for high voltage lines, lower voltage lines carry more current for a given amount of power and will experience higher losses.

This isn’t a good answer. On average in the US we lose 7% of power in transmission and 8% in power conversion. I pulled these numbers out of thin air, but it’s probably accurate to within a factor of 2 for wherever you are. A home solar power system might mean 7% lost in dc to ac and then you still lose 8% for conversion so basically 5-20% of all the power you produce is lost before it reaches its destination.

A more didactic answer might start with defining power, P=IV (power equals current times voltage) and “ohm’s law” V=IR (voltage equals current times resistance) and suggest this means that the power lost to the resistance of transmission line with resistance R is P=I^2R. Since the current you send is proportion to the voltage (One megawatt can be 1Amp at 1000000 Volts or 1000Amp at 1000 Volts, you want to use as high voltage as possible when transmitting long distances. The limiting factor on voltage is the amount of insulation required.

Usually power transmission uses three-phase alternating current, which sends power by varying the voltage on three lines each 120 degrees (1/3 period) offset from one another. It’s reasonable homework to read about why AC is better for transmission and also how three phase AC works and determine the economic value of laying three cables instead of two, with variables for the cost of wire, fixed costs per mile, and cost of electricity. ~50% of transmitted power is used to drive three-phase synchronous AC motors.

Resistance is related to the resistivity (denoted with a Greek rho) of the material and the cross-sectional area (denoted A) and length (L) of the wire: R=rhoL/A Resistivity is a fundamental property of materials and is related to the free movement of the outer shell of electrons of atoms in a crystal lattice.

Superconductors do not have resistance and can carry an extremely large current as a result. Unfortunately superconductors have a maximum magnetic field capacity and require extremely low temperatures requiring cooling with liquid helium or nitrogen.

There is no such thing as a dumb question and if there is one thing that I love about HN it is that people will take the time to answer questions.

Not only will people answer, it's answers from people who actually know (and are willing to share).

What's the highest pressure that can be achieved over a useful (1 meter?) distance? I find it amazing that they managed to scale up cryostats to 1km for superconducting powercables at low temperatures - it would just be interesting if they started scaling up high pressure environments.

I understand that the achievement in question was made in a high pressure environment; but if we get room temperature superconductors (at standard atm pressure), does that mean large scale hover cars/boards deployment will be viable as well [0]?

[0] https://youtu.be/PXHczjOg06w

Room temperature super conductors are in the category of materials that will cause semi-magical transformations in society along side generation techniques that make .001$/KwH electricity, 1$/kwh electricity storage, or >200 gigaPa tensile strength materials for cheap.

It depends on how much it costs.