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Using Superconductors as Insulators
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?
--Bob
1^2=1; (-1)^2=1; 1^2=(-1)^2; 1=-1; 1=0.
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.
Thanx Doug...
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.
cya
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.
cya
I may as well explain (very basically) how CMOS technology works, so you can get an idea.
;))
.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.
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
æeee!
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?
æeee!
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.
-AS
-AS
*Pikachu*
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.