Have we done
'Mind the pseudogap' yet?
Physicists may be one step closer to cracking the mystery behind high-temperature superconductivity, as they confirm that a new distinct state of matter forms just before a material enters its superconductive state. Superconductors conduct electricity with zero resistance, a desirable property that is severely hindered by the …
Using these oxides makes sense because there is plenty of data available. It appears that there is something going on that the current theories miss entirely with superconductivity. If that is true, then there is a possibility of finding materials that superconduct at ambient temperatures.
I was working in Cambridge when the first LN2-temp superconductors were discovered -- the pub convos were *interesting*. People were frantically trying to get hold of quantities of yttrium and other odd elements. I suggested they try contacting Brock's Fireworks.
True but that suggests it's been well tested and well characterized. Handy if you're going push something into the unknown. REBCO (Rare Earth, Barium, Copper) based superconductors have made massive strides in current capacity, which is why MIT think they can build a torus the size of Jet and yet get actual power out of it.
An interesting question would be "Do all superconductivity theories predict this pseudogap" ?
Obviously those that don't can probably be discounted. However ff none of them did then this really is unknown territory, possibly Nobel grade. Otherwise it's a case of finding the differences between what kind of pseudogap it will we and trying to find an experiment to tell them apart.
Exciting times for both experimental and theoretical physics.
I'm not whiz-kid at this, but would different materials show a slightly different pseudogap in structure and not just temp? I realize they're using a standard material of known properties so I'm wondering/thinking that other materials would act differently. The gap would exist but just "different"...?
Like I said, I'm not whiz-kid. Don't know all that much about this but yes.. exciting times.
Another excellent question.
REBCO's are a family so changing the rare earth used (not actually that rare, as the Chinese found out) and tweaking the proportions gives you lots of variations. Lots of possible results here.
All the same, all different, maybe some have no gap etc.
The pattern should help to pin down a definitive theory (or at least the "shape" of a definitive theory) even more.
An actual theory offers the chance to find out the limits of current carrying (very important for magnet applications) and maximum operating temperature. How close we are to them and can we design better ones from first principles.
"[...] tweaking the proportions gives you lots of variations. [...]"
In more mundane mixtures - water freezes at a lower temperature if salt is added.
It also freezes at a lower temperature if anti-freeze is added. However the mixture behaves in a eutectic fashion. The lowest temperature is achieved at only one ratio. Adding more antifreeze than that will decrease the effect.
" tweaking the proportions gives you lots of variations. Lots of possible results here."
yes. different alloys exhibit different properties when solidifying, for example. The ideal ratio for leaded-solder is about 63:37 lead:tin, which has almost NO plastic region during the cooling phase, giving you a nice shiny solder joint. This is unlike typical lead-free solder, which is typically grayish and dull in appearance [like a 'cold joint' done with leaded solder].
The proportion of lead and tin determine the cooling phase behavior. This is easily observed and well documented. It stands to reason that alloy make-up could have SIMILAR effects on OTHER 'cooling region' type things, such AS this 'pseudogap' state.
I suspect that the pseudogap behavior, as well as superconducting behavior, is either hyperdemensional, or related to quantum states *like* quantum entanglement.
The 'hyperdimensional' idea is that electrons in clouds "behave that way" because they're moving (and possibly oscillating) in dimensions we cannot see or perceive, and so they appear to be randomized probabilistic "now you see it, now you don't" clouds rather than some kind of recognizable "orbit" pattern that can easily be observed and measured. [In My Bombastic Opinion] the quantum world seems to be expressed in probabilities, rather than fixed positions [until you collapse to wave functions by measuring/observing].
So I'm just proposing that this, if tied in with quantum mechanics, might make a whole LOT of sense. Then 'an explanation appears' [from a theoretical physics perspective] and maybe they're one step closer to room-temp superconducting power storage devices...
"Water is a random jumble of H2O particles and has no symmetries, but as soon as it turns to ice the molecules arrange themselves in hexagonal structure. It no longer looks the same in every direction – its rotational symmetry has broken."
I'm not a materials scientist but this statement is confusing. Surely the rotational symmetry is broken when ice melts, changing from an ordered hexagonal structure to a random jumble of molecules (rather than particles)
It works both ways. Water has a symmetry that is random, that random symmetry is broken when it solidifies. The hexagonal structure has a hexagonal symmetry, which is broken when it melts to become random.
Basically, the term rotational symmetry is just a way to say that the structure has changed in such a way that it just hasn't realigned to another axis, it has actually changed in a non-similar way.
Pretty cool stuff with this pseudogap either way though! :)
Adding latent heat of fusion (to melt ice) probably adds entropy to the system, and the entropy would be responsible for breaking the crystalline barriers as the solid melts. The converse would also be true (when freezing).
I wonder what effect 'removal of entropy' has on solid structures, and whether THAT is responsible for superconductivity?
my understanding of the 'time reversal' theory is the "now you see it now you don't" observations that sometimes occur with things *like* electron clouds. Or so I've read/heard. It's part of the theory that 'hyperdimensionality' is causing these, i.e. motion/oscillation within dimensions we can't perceive. M-theory suggests 11 dimensions last I checked. THAT is what I'm thinking of at the moment.
Tardis reference appreciated, though.
"[...] those new age hippies do when talking about the power of 'crystal energy'. "
Haven't heard that since the 1970s. The part-built Findhorn assembly hall was said to be designed with a crystal at its apex. Once completed it was claimed it would make them independent of the electricity grid.
Practical applications for a room-temperature superconductor?
Really efficient motors. Really efficient power converters. Really efficient long-distance power transmission. Mostly the same stuff we do now, but smaller and with less wasted energy.
You can also use them to make things hover a short distance, which is good for bearings and silly toys.
To the Editor,
Sir, one of your journalists has left the phrase "the new phase enters a completely different structure that breaks time-reversal" in an article with no other comment or explanation.
Will you please see to it that some explanation in the most prosaic and banal terms is introduced as soon as possible since I am very much afraid that otherwise my brain will explode.
Yours truly,
Perplexed of Tunbridge Wells
it's more like hysterysis than particle physics CPT violation. And they've used the phrase 'cos it sounds sexier.Quoting the paper:
Nernst effect, terahertz polarimetry and ultrasound measurements on YBa2Cu3Oy suggest that the pseudogap onset below a temperature T∗ coincides with a bona fide thermodynamic phase transition that breaks time-reversalThere's nothing particularly unusual about breaking of time-reversal in thermodynamics. If I smash a vase with a hammer, the vase breaks into pieces. What we never see is a vase spontaneously reassembling itself and a reverse hammer blow.
"the new phase enters a completely different structure that breaks time-reversal"
The only picture my mind produces is that there are different sequential structural organisations when entering/leaving phase change states.
So for water it goes from liquid to solid - and if you change the temperature/pressure it goes from solid to liquid. There is (apparently) no pseudo-gap state in either direction.
My guess is that the pseudo-gap state only occurs before entering the superconductive state - but does not occur on reversing that final state. As I say - purely a guess at the terminology's meaning.
Some element of logic would indicate that there should be some state between structurally different states, for example, solid and liquid because during this transition the structure is changing from one very different structure to another. Whether or not this transitory state is a state that the matter is stable enough in so it can be "persuaded" to remain in for any period of time is likely a very different question.
"Some element of logic would indicate that there should be some state between structurally different states, for example, solid and liquid"
But the same element of logic would indicate other states between solid, the interim state and liquid. And iteratively...It's states all the way down.
It sounds more like processes of changing states. In the water/ice case there are already names for them: freezing and melting. That raises the question of whether this pseudo-gap is actually a state or simply a process of becoming or ceasing to be a superconductor.
"It sounds more like processes of changing states. In the water/ice case there are already names for them: freezing and melting. That raises the question of whether this pseudo-gap is actually a state or simply a process of becoming or ceasing to be a superconductor."
But what if it ONLY occurs ONE WAY: going TO the semiconductive state, but not FROM it? Thus the talk of breaking symmetry.
or is the Liquid phase the pseudogap between Solid and Gas?
Based on nothing but my reading of this article, I took the use of the term pseudogap to mean that the phase exists only for an extremely short period of time - for example if a material changed from solid to liquid at 10°C, but then changed from liquid to gas at 10,5°C, you could refer to the liquid phase as a pseudogap. Only I'm pretty certain they are referring to a MUCH smaller gap then 0,5°C.
But then again I could be COMPLETELY wrong! :)
This post has been deleted by its author
"But secondly "cooled before the material reached its critical temperature"? I need an explanation"
As far as I can this is simply the author of the article attempting to say that the pseudogap phase is observed at a slightly higher temperature than the critical temperature (ie. the temperature at which it becomes superconducting). It seems to be incredibly awkward phrasing bordering on gibberish from the author of the article, and not from the actual paper. Probably caused by the fact the author clearly has no clue whatsoever what the research is actually about. Nothing new has been discovered at all. The pseudogap region is well known and has been studied extensively before, with this paper providing a raft of references to previous papers looking at it in a variety of different ways. As is all too common with the media these days, what is heralded as an amazing new discovery is actually just the normal progression of science investigating a known phenomenon in more detail.
@Uffish
"Sir, one of your journalists has left the phrase "the new phase enters a completely different structure that breaks time-reversal" in an article with no other comment or explanation.
Will you please see to it that some explanation in the most prosaic and banal terms is introduced as soon as possible since I am very much afraid that otherwise my brain will explode."
Time-reversal symmetry (https://en.wikipedia.org/wiki/T-symmetry) is basically the statement that everything is basically the same if you reverse time; the laws of physics don't change and everything carries on as before, just backwards. However, there are a variety of ways this can be broken. Magnetic fields and angular momentum, for example, are axial vectors that add an additional change of sign when things are reversed or reflected (see the diagrams on this page - https://en.wikipedia.org/wiki/Pseudovector). This means that they can break T-symmetry because if you look at the dynamics of a microscopic system with magnetic fields in it, things won't actually be the same if you reverse time (see https://en.wikipedia.org/wiki/Microscopic_reversibility). When it comes to this paper in particular, they're looking at the effect of the material (specifically the electrons inside it) on reflected laser light, and how that depends on the orientation of the sample (a single crystal). What they show is that at higher temperatures, T-symmetry is not broken, but it becomes broken at a temperature higher than the critical temperature showing that there is a different phase present between the normal and superconducting phases (or more specifically, showing what the properties of that phase are, since the phase itself was already known).
I make no promises for how exploded heads may be after reading this, let alone if you actually try reading the links or doing any of the maths.
At school we were taught that at "normal pressure" pure water freezes at 0C and boils at 100C. Like all things in Physics the explanation was "good enough" at that stage of our learning.
The "normal pressure" qualifier didn't make much sense - until we saw people trying to make a cup of tea on a mountain. The lower air pressure meant the water boiled well below the tea's optimum infusion temperature.
At the other end of the scale is the supercooling of pure water below 0C. It remains in the liquid phase until it is given a knock - whereupon it instantly goes to the solid state.
Question: does a "sublimation" chemical only have solid and gaseous phases - or is there a liquid phase that is too unstable to observe normally?
"Question: does a "sublimation" chemical only have solid and gaseous phases - or is there a liquid phase that is too unstable to observe normally?"
It all depends on the conditions. Freezing and boiling points are dependent on BOTH temperature AND pressure. It's just that in some cases like CO2, atmospheric pressure is so low that you go past what's known as the Triple Point (the point where all three phases can coexist). Below this pressure, liquids can't form, and you get sublimation instead. If you pressurize the CO2 (to, say, 5.2 bars), you can get it into a liquid state.
Liquid nitrogen is not terribly expensive. It used to cost about the same as beer. And there's a lot of nitrogen about, just needing a rather good refrigerator to cool it, as it comprises 80% of the atmosphere. The supply of helium is in contrast rather limited and it needs a special multi-stage refrigerator to liquify it.
It's not the the cost of the liquid nitrogen. It's the cost of keeping it liquid!
The energy (currently) needed to keep even a high-temperature superconductor cool is more than the energy that is lost by a normal conductor. Add in the extra cost of the superconductor itself and that's why we seldom use superconductors to transport electricity.
"Liquid nitrogen is not terribly expensive. It used to cost about the same as beer."
Expensive relative to what though? A single beer might not be particularly expensive in absolute terms, but buying several of them every day for many years is much more expensive than not buying them. When you consider that savings from resistive losses in most applications are likely to be pennies per day at the absolute most, that's an awful lot of beer-equivalents that have been wasted on something other than beer.
To put things in perspective, I work at a particle accelerator that uses several MW of electricity to power hundreds of magnets that run anywhere between a couple of hundred to a few thousand amps, as well as a variety of other high power components. We get through tons (literally) of liquid nitrogen for things like cooling detectors and samples, but we use precisely zero superconductors to run the actual accelerator; even in such a highly specialised setting that already has the supply infrastructure set up, it's simply not worth the cost to use superconductors to reduce your energy bills.
Water is a random jumble of H2O particles and has no symmetries
Really? Water Clusters: Introduction
Image of 280 molecule, 3 nm diameter structures here. Each 280 molecule contains 8 different subclusters. I seem to recall Lynn Margulis saying something like "random means I don't understand it".