Nanowire could provide a stable, easy-to-make superconducting transistor

> In 1956, MIT electrical engineer Dudley Buck published a description of a superconducting computer switch called the cryotron. The device was little more than two superconducting wires: One was straight, and the other was coiled around it. The cryotron acts as a switch, because when current flows through the coiled wire, its magnetic field reduces the current flowing through the straight wire.

> [Karl Berggren] dubbed his superconducting nanowire device the nano-cryotron in tribute to Buck... The nano-cryotron uses heat to trigger a switch, rather than a magnetic field.

Dudley Buck's cryotron:

https://en.wikipedia.org/wiki/Cryotron

This is quite a convoluted way of making an electrical switch. In brief, the carriers of supercurrent (Cooper pairs) in the channel are "depleted" (actually: broken up) by a local heater that raises the channel temperature above the superconductor's critical temperature.

The circuit topology, a heater coupled to a superconducting wire to sense the local tempreature, is the same as in a transition-edge sensor (TES), and functionally identical to a supercondicting nanowire single-photon detector (SNSPD). [SNSPD does not have a separate heater.] These cryogenic detectors are typically used when a good electrical amplifier does not exist for the input radiation. A textbook example would be optical or x-ray photons.

I believe the device will be terribly inefficient as a transistor. The root cause is that the electrical signal gets converted into heat and back: Heater current -> Electron heating -> Phonon (lattice) heating -> Breaking of Cooper pairs in the channel -> Suppression of (super)current. Once the heat is in the phonons (lattice vibrations), it can propagate anywhere in the chip substrate.

Also, the active area needs to be continuously heated to maintain the resistive ("off") state.

Since HN is mostly a computing-oriented forum: This transistor will not be used for general-purpose logic cricuits.

Not really clear to me why the choke wire needs to be superconducting too, or indeed if it really is superconductive in any important sense of the word. The point seems to be that the choke wire quenches easily and provides heat from internal resistance.

Also, this sounds like it is purely a switching transistor since superconductors aren't really grey-area type of things, you get them in the superconducting state or in the normal state and the transition is about as smooth as that from water to steam.

If laptops had superconductors would the battery life increase?

Also am I thinking too small for the potential of superconductors?

I like the idea a lot and am not criticizing this article, it's author, or the concept, but a few quick "minor corrections" if I might:

>"Superconductors — materials that conduct electricity without resistance"

"Superconductors — materials that conduct high amperages at low voltages without heat"

>"Most metals lose resistance and become superconducting at extremely low temperatures, usually just a few degrees above absolute zero."

Most metals, even small cross-sections -- can already conduct huge amounts of amperage -- but the electricity so passing must be conditioned so as to be at a high enough voltage -- to prevent heating effects.

A good example of this would be a high-voltage transmission line; those tall steel towers carrying aluminum cables.

The amount of electricity that they carry is enough to melt a small building -- but the cables themselves, despite being much smaller in diameter, never melt -- why is that? -- this is because the electricity is at high voltage...

So is metal with electricity running through it at high voltage a superconductor? Technically not, because there are power losses over long enough distances.

Also, it would not surprise me if everything (every metal that is, and possibly non-metals as well) -- becomes superconducting at a few degrees above zero...

In other words, superconductivity -- might be more of a property of temperature -- than it is of the underlying material...

Now, combine that idea with the idea that electricity can be conditioned in various ways to enable greater degrees of conductivity (voltage is one, frequency is another) -- without heat -- and then we might have a larger understanding of the underlying Physics...

That being said (and I hope it was not taken as a criticism -- it was not intended to be!),

I do like and appreciate very much the idea of superconducting nanowire!