[HN Gopher] Nanowire could provide a stable, easy-to-make superc...
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Nanowire could provide a stable, easy-to-make superconducting
transistor
Author : el_duderino
Score : 36 points
Date : 2021-02-11 13:20 UTC (9 hours ago)
(HTM) web link (news.mit.edu)
(TXT) w3m dump (news.mit.edu)
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| nickthemagicman wrote:
| If laptops had superconductors would the battery life increase?
|
| Also am I thinking too small for the potential of
| superconductors?
| ben_w wrote:
| Yes to both, if you can do it at STP. Superconductors make
| practical many things which are otherwise extremely expensive
| or just plain impossible.
| simiones wrote:
| By my understanding, a superconducting computer does consume
| less power than a traditional computer, even taking into
| account the cooling systems.
|
| However, superconductivity requires either extremely low
| temperatures (a few kelvins at most) or even more extreme
| pressures (think many kilometers underground), so it is
| currently outside the realm of possibility for a mobile device.
| nynx wrote:
| actually, it's more like within a factor of two of the
| pressure at the center of the earth.
| SiempreViernes wrote:
| Well, some types of superconductors work fine at the simply
| low temperatures provided by liquid nitrogen (77 K).
|
| Though there are other factors like ability to be made into
| wires and how much current they can carry before switching
| out of superconductivity you might be having in mind with
| your single Kelvins number.
| SiempreViernes wrote:
| 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.
| sradman wrote:
| > 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
| peter_d_sherman wrote:
| 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!
| BenjiWiebe wrote:
| Personally, I find the original more accurate and clear.
| _8091149529 wrote:
| 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.
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