Superconductivity is kind of like the red headed stepchild of physics. People seem to shy away from it. Several Nobels have been handed out to scientists for developments in the field but I doubt if one person out of a thousand could name any of them. When breakthroughs are made in other areas such as the Higgs field and detecting the first gravitational waves they make headlines and capture imaginations. But when you see a headline that states: "New Quasi-2D Superconductor Bridges Ferroelectric Insulator" everyone takes a collective yawn. Me included. It's not interesting (to me) and it's difficult to understand. In my 70 years I've probably read 20-30 books each on quantum, classical and astro-physics. Not to mention many hundreds of magazine articles (when there were magazines) before the internet. I find it interesting, fascinating and as Einstein put it, a bit spooky. I enjoy discussing it when the opportunity arises. It's my loss I suppose but I haven't put any effort into understanding superconductivity. I just don't know enough about it to discuss it.
it is left out. and i think its largely because we cant theoretically explain why it works. we know it works, and what it takes. and even some of the supercoliders use it. so we have a practical, functional knowledge of it. but the great why still sits there. and it seems like another quasi/possible case of quantum stuff happening. to the continuous loop/storage of energy, one article (it might have been the one you mentioned as that is what started me down the path) said they have a real example of a loop working for 23 years with no drop in energy. although I didn't see a reference for where that is actually taking place.
right now even just reading the wikipedia pages takes me several tries to fully swallow the concepts or just follow what they are saying. This is the type of stuff I would have devoured before my concussions, and would love to talk with my uncle about.
so just because I am on a nerd roll, and I am somewhat sensing a desire on your part to understand here we go, as I understand it.
conceptually anything element/molecule/whatever at absolute zero is a perfect conductor, meaning no interference or energy loss to an electrical current applied to the substance. but seeing as how absolute zero is another of those things just out of our reach for forever, superconductors are the next step. One of the reasons they aren't just "perfect conductors" is because when something reaches a superconducting phase it has other shared properties besides the non resistance. there may be more than two things, but as far as I remember these are the two other things they mentioned. 1. Ejection of weak magnetic fields. 2. Sudden phase shifts.
So to item 2 first, and this kinda explains what happens. You take one of these compounds and as it gets colder and colder its resistance drops by some fixed ratio, compound specific. But when it reaches some critical temperature, again compound specific, that resistance will suddenly drop to zero. It is at that moment that the magnetic fields are also ejected. So the thinking is that a superconductor isn't so much a "thing" as much as it is a "phase" like liquid, solid, gas. they can apparently make a lot of different materials enter a superconducting phase, each has its own critical temp. once it has reached that critical temp, further cooling does nothing as far as they can tell. and many of these materials are very dissimilar to each other, so its not like there is a magic element to add or anything.
The "hottest" superconductor they have found reaches that state at 135K, or -217 degrees Farenheit. so still really fricking cold, but a temp that liquid nitrogen can reach so its much more attainable. most are more in the 30K range (-405), and it takes some very specific conditions to reach that 135.
now this is where things get weird. heres a link to the weirdness, imo.
Cooper pair - Wikipedia
So my understanding is that it may not be just the material that changes, the actual electrical charge also changes. More of these Cooper Pairs are present in a super cold super conductor. these pairs don't bounce around like normal electrons causing themselves to lose/pass on energy from the charge itself. in the paired state they don't bounce but just move. what I am thinking I am reading here is that one electron from the electrical charge forms this Cooper Pair with an electron from whatever supercold material. these pairs exist because there bond is so weak that even a little thermoenergy (heat) can break the bond. but at these lower temps these electrons can do this.
So where I go back to being fuzzy is I am not sure what exactly this pairing means. as it sounds like Cooper Pairs dont have to be close to each other, so its not like the electrical charge is "trapped" per se or held in place. but it also says that the electrical charge, which can normally be thought of as a fluid, is now a superfluid. so it sounds like the electrical charge is changing as well. but again I don't know what that means when it comes to superconductors. it just means that it can flow without losing energy, because they aren't bouncing off of things, but nothing tells me if they are still moving, or how their movement is different after this pairing. one article related it to glass, glass is a liquid, it just flows really slow, so maybe that is what is happening with the current? Or maybe the electrons just float around their pairs and don't move away, but just keep circling maintaining a set distance and speed? again IDK and I haven't seen an explanation.
so now to item 1. as I said before the rejection of magnetic fields happens at the same time resistance drops. wikipedia has some images that explain this. but basically magnetic fields can usually pass thru anything, as long as another field isnt interferring. and so for normal, non magnetic items, these fields pass as straight lines. but once a superconductor reaches that state suddenly the magnetic fields will pass around the object. now this part of the state can be broken by a high enough magnetic field, what I don't currently understand, is if once its broken it loses its non resistance as well, even if still super cold and everything. which raises the question to me of how electricity and magnetic fields interact already. so on the magnetic side some materials work differently than others. some have a thin layer where the magnetic fields still pass, but others completely eject them. again this is completely material specific and not cold specific. and this is also tied to what happens when they are no longer super cooled.
item one is why you see all the cool photos of objects floating. its not two magnetic waves pushing against each other, its one magnetic wave pushing against the object. so this floating also helps keep things cold, and any other interference from happening.
anyway nerd rant over. fascinating stuff to read about if you dont' mind the headaches.