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Using Superconductors as Insulators 37

slambo writes "Nando Times is reporting today that Swiss scientists have discovered a way to turn a superconductor into an insulator by applying an electric current to it. " Almost zero details in the story itself, but the whole idea really appeals to me. Anyone have more details about it?
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Using Superconductors as Insulators

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  • Posted by FascDot Killed My Previous Use:

    Great, now we just need a way to change gold into lead.
  • Posted by FascDot Killed My Previous Use:

    Great. I ruined THAT joke.
  • At whatever temperature the superconductor functions. If it's superconducting, it won't give off heat, as it has no resistance.
  • *All* superconductors have a limit to their current carrying - this is because the Magnetic fields generated by the current tend to disrupt the cooper pairs. So - build a suitable supercondictive circuit and you can turn the flow of current between two points on and off...

    Well it#s probably some interesting new design that they're really interested in.
  • by mcelrath ( 8027 ) on Friday May 14, 1999 @07:57PM (#1891841) Homepage
    Is here [sciencemag.org]. (From Science Magazine)


  • However, being a cuprate-oxide it is a bummer of a material to work with. Until someone figures out a reliable fabrication and processing technology then high-tc superconducting computers are just nice things to try and get grant money with. But then since I only work with metals superconducting below 1K I would say that...
  • This is just a Josephson Junction Gate.

    Back in the 1970's IBM researchers invented the
    Superconducting Josephson Junction Gate. In the
    1980's IBM produced a 1ns 1kx8 ram chip that ran
    at a temperature of 2.5 Kelvin.

    The Josephson Junction Gate is made of a strip of
    Superconducting material that has a high resistance
    when it is not Superconducting. Above the gate
    strip is a single turn coil of a superconducting
    material that generates a field that will exceed
    the critical field for the strip and turn it
    non-superconducting. The Coil is connected to the
    input and the gate strip is connected to the
    output. The Josephson Junction Gate functions like
    a field effect CMOS gate except that it switches
    current instead of voltage.
  • I beleive this is incorrect.

    The Josephson Junctions in my lab work a little differently. A very thin (about 10^-9 m) insulator is put between two superconductors, like a sandwich. The insulator is never superconducting. If a voltage is applied across the junction (greater that 2*superconductingbandgap/e) the junction behaves like a regular ohmic resistor (V = Ir). But smaller voltages produce very fast oscillation. Its not that its an insulator, its just that the current is oscillating back and forth so fast the the net current is 0. The oscillations are something like 500GHz/Volt. This gives sort of an odd effect where if the voltage across is zero, there is on current, but if there is a voltage, the net current is zero.

    Feynman does a pretty good job of this in Feynman Lectures, Vol 3, chapt 21, I think. It one of the chapeters at the end.

  • Superconductors not only have a critical temperature, below which they are superconductors, but also critical magnetic fields, below which they are superconducting. Critical Temp is usually on the order of liquid helium (4.5deg K) for elemental superconductors, and liquid nitrogen (70 deg K) for "High Temp" ceramic supercouctors. Critical magnetic fields are something like kilogauss to Tesela.

    It is difficult to switch temperatures back and forth quickly. but its easy to turn magnetic fields on and off quickly.

    Ceramic superconductors (unlike elemental SC like lead and vanadium) are good insulators when they are above the critical temperature/magnectic field curve.

    If you wrap superconductor A in a loop around SC B, passing a current through A, and the loop was small enough/current big enough, the magnetic field produced through B would cause it to become an insulator. As soon as the current was turned off, it would be a SC again. Hence a gate.

  • by sig ( 9968 ) on Friday May 14, 1999 @03:06PM (#1891846) Homepage
    Quantum Mechanics allows electrons to fill a finite number of states. Since electrons are fermions, they obey the Pauli exclusion principal: No two electrons can be in the same state at the same time. When you have a lare sample of something (like a copper wire) there are a bunch of states at the top, and most of them are unfilled. Insulators have no empty states, so there is no where for them to go. Conductors have lots of empty states, so they just glide along.

    At superconductor temperatures, the vibrations of the atoms slow way down and the electrons tap in to these low freq vibrational modes (called phonons, but thats not importart) causing a net attraction between electrons. Which is wierd because normally electrons repel each other.

    So then the electrons pair off (into Cooper Pairs, but still not important) but these pairs are no longer fermions. (This is the important part) Instead the pairs behave as Bosons, which don't obey the Pauli exclusion principle.

    All the electron pairs end up in the same lowest energy state. Now when they travel, they all travel together, but they never have to worry about finding an empty state, so they don't loose any energy.

  • It's not like this is anything new. The Peltier effect seems quite similar (the use of two dissimilar semiconductors to direct heat). I read an interesting article [orst.edu] that explains it quite well. I assume this new "insulator" is something similar, or works on the same principle.
  • It's not like this is anything new. The Peltier effect seems quite similar (the use of two dissimilar semiconductors to direct heat). I read an interesting article [orst.edu] that explains it quite well. I assume this new "insulator" is something similar, or works on the same principle.

  • Trying to represent ones and zeroes by switching
    voltage levels like in semiconductor transistors
    is not the best way to utilize superconductors.
    Take a look RSFQ logic:


    They represent bits with quanta of magnetic flux.
  • by Rayban ( 13436 ) on Friday May 14, 1999 @11:46AM (#1891850) Homepage
    I may as well explain (very basically) how CMOS technology works, so you can get an idea.

    There are two types of CMOS transistors: NMOS and PMOS. The only difference between them is in how they are "doped" (impurity ions injected into the silicon where they lie), as one is the opposite of the other (where NMOS is doped with an electron acceptor, PMOS is doped with a electron donor and vice versa).

    NMOS = n-channel metal-oxide semiconductor
    PMOS = p-channel " " "
    pronounced "enn-moss" and "pee-moss" (duh ;))

    Here's an easy way to think of these:

    CMOS transistors have three pins. One of them is the "gate" and the other two are the source and drain, where current will either flow or not.

    An NMOS transistor acts like a switch that turns "on" (closes the circuit, making a path from one switch terminal to the other), when you apply the Vcc (the voltage representing a digital "1") to the "gate", which is the top of the transistor.

    A PMOS transistor works in the opposite way, conducting a current when there is a digital "0" (usually 0V) applied to the gate.

    If this sparked your interest, go to a bookstore and pick up a basic digital electronics book. It'll take you through some of the related physics (which are pretty cool) and you'll learn too.

    BTW, if you've ever wondered what .25 micron and other numbers mean, that's basically one of the dimensions of the transistors in the chip. Smaller transistors mean less heat and faster circuits.
  • by Rayban ( 13436 ) on Friday May 14, 1999 @11:34AM (#1891851) Homepage
    Well, I guess the paper doesn't really explain how this can be useful. The difference between a standard transistor and a transistor I assume that would be made from this is that the logic would be controlled by unrestricted current flow, as opposed to voltage (well, *technically* standard CMOS logic relies on current, but it's essentially voltage based).

    The setup for creating the standard logic gates would be similar to the CMOS version and probably wouldn't take anyone longer than an hour or so to flesh out.

    The advantages:
    - *zero* power loss in the transistors: this means almost zero power consumption in the chip
    - low-to-zero capacitance in the transistors: computers that operate at the speed of light (electrons moving as fast as physically possible)

    I don't know if the switch between conductor/insulator is infitesmal or requires a fairly large time to occur, however. I guess we'll see in a few months.

    Exciting technology.. any more info, anyone?

  • An oxymoron if I have ever heard one ...

    But theoretically it would make it easier to make even FASTER processor etc ...
  • Using the critical magnetic field to turn the gate on and off would work, but it's hardly a new phenomenon, so why would it suddenly appear as a news article?

    Also, how would you produce gates of this type on a microchip? I'm not terrbily famliar with the process, but it seems that it would cause considerable difficulty to try and do this at a nanometer scale. Perhaps that is part of their "discovery"?

  • You could use it to make a basic logic gate. So long as you can then make a not and and or or, or either a nand or nor then you can make any logic circuit.

    The telling tale will be what the energy consumption and timing is like.
  • Correct me if I'm wrong, but aren't most superconductors ceramic? And don't ceramics make rather good insulators or their own. (Provided they aren't super cooled.)

    Of course the idea that we can have a piece of super conducting wire insulating itself is rather nifty.
  • As far as I know, we don't actually have a real model to explain exactly how superconductivity works, other than intuitive guesses...

    IIRC, a superconductor is impervious to magnetic fields, and also happens to freeze the magnetic field already around it when it happens to turn superconductive.

    There is also a relationship that magnetic fields can induce current flow, and current flow induces magnetic fields, right? I wonder if that is the principle behind this perfect insulator; magnetic flux lines or something frozen in such a way that it actually inhibits current flow, at least in some directions.

  • One big question - at what temperature would something like this run? Keeping chips cool is hard enough without having to get to superconducting temperatures!
  • This makes sense to me. If I remember right, the current crop of "high"-temperature superconductors are very similar to types of ceramics, which can be great insulators. Also, the superconductor theory that I remember involves pairs of electrons transiting a crystal like structure in which the "steady-state" fields were all balanced.
  • by Merk ( 25521 ) on Friday May 14, 1999 @11:43AM (#1891859) Homepage

    Ok, I have a physics background and one class I vaguely remember mentioned how superconductors work. If I remember correctly superconductors work because they make paths where the internal fields balance out so precisely that any electron propelled down one of these paths encounters no resistance.

    This is in opposition to regular conductors where you essentially have a cloud of electrons and a field puts a net shift in the cloud, resulting in a net movement in the cloud.

    My guess is that this is something like the Hall effect. The current they introduce shifts the fields around inside the superconductor itself and kills the properties that make it a superconductor.

  • Generally meaning that it will work effectively when chilled with liquid nitrogen. That's much better than liquid helium, but "better" is relative...
  • This is one of the least informative "articles" I have ever read.

    'Something exciting happened. It has something to do with superconductors maybe.'

    Gee, thanks. This must be what premature ejaculation is like.
  • Last time I've heard about it (in 1995, at the 21st Low Temperature Physics conference), experimental samples of the superconducting integrated circuits were already built and running at 300 Gigahertz - with the 3.5 mkm technology. I only wonder what's the state of the art now, four years later.

    However, the superconducting circuits are not based on conductivity switching, like the semiconductor ones - instead, they switch and exchange the magnetic flux quanta.

  • If I understand some of the discussion here, then a superconductor stops having zero resistance as soon as you draw enough current through it, because you generate a magnetic field that screws up the superconducting properties (i.e., it gets a nonzero resistance). This seems at odds to me with some of the things they use superconductors for, like very strong magnets. Are they just using a very thick "wire" of material, to keep the internal field strength low?

    This makes superconductors seem more useful for computing (low current/voltage) and less useful for things like power transistors, which was my first thought for an application when reading the blurb.

    If I understand some of the other discussion here, then all they found was that if they doped a known superconductor with some other material, then they could adjust the critical temperature a few degrees by applying a current. That is a much less general result, and it makes more sense to me. Not sure what applications behavior like that has... a thermometer that works on a very narrow range, operated by bisection (numerical methods sense)?

    Someone who understands the physics better, please enlighten me.

  • well, *technically* standard CMOS logic relies on current, but it's essentially voltage based

    No it doesn't. Voltage at the gate is what creates the channel that allows current to flow between the source and the drain. Ok, current is needed to overcome the gate capacitance, but it's voltage which makes the switch flip.

    Ironically, though, CMOS circuit designs are dominated by current considerations. That's because the gate capacitance and the capacitance of the metal wires becomes very important for ICs, so to get that required voltage change, you need to push a lot of current into those capacitors.

    So I would have said:

    well, *technically* standard CMOS logic relies on voltage, but it's effectively current based

    (Ok, if that's what you meant, then I appologize. :-)

  • experimental samples of the superconducting integrated circuits were already built and running at 300 Gigahertz - with the 3.5 mkm technology.
    Er, I find that hard to believe. A 300 GHz machine would have a clock period of 3.3 picoseconds. In 3.3 picoseconds, light travels only one millimeter. Thus, a 300GHz processor would have to fit entirely within a sphere 1mm in diameter. Was that the case with the processor you heard of?

    And what's "3.5 mkm"? Are you talking about 3.5nm? AFAIK, that's an order of magnitude smaller than the smallest semiconductors they can fabricate now, so I find it hard to believe a new technology could be made so small.

    Sorry, but I'm not convinced. I think you heard wrong.

  • The article (more like a blurb) seems to make it out to only work with this certain superconducter operating at low temperatures. What low temperature? Liquid nitrogen? Liquid helium? What? Until it works at room temp (or at least 0 degrees celcius), don't expect it on the desktop any time soon...
  • Lets cut back on electric.The 2yk scare we'll all eat by candelight and have no money,all in banks.BULL

How can you do 'New Math' problems with an 'Old Math' mind? -- Charles Schulz