Silicon Superconductors

Diana writes "Physicists at CNRS have demonstrated superconductivity in silicon, the element long known for its semiconducting properties. High doping is the key — by substituting 9% of the silicon atoms with boron atoms, it was found that the resistance of the material drops sharply when cooled below 0.35 K. A small increase in the transition temperature is likely with further work."

Comments

0.35K is rather cold

[NixieBunny]

I realize that this is just a laboratory curiosity at this point, and no one would try to use such a compound commercially. Still, a brief description of what it's like to make 0.35K is in order.

I work on a radiotelescope that uses receivers cooled to 4K. These use a helium refrigerator that works just like the Freon thing in your car but using helium instead of Freon as the phase-change medium. It takes three stages of cooling (with compressors and heat exchangers) to get to the 4K point. It also takes 10 kW of electrical power to cool one watt of load to 4K.

We until recently had one receiver, a bolometer, that was cooled to 0.4K using the 3He isotope of helium that has a lower boiling point. The refrigerator for this is a fist-sized gadget that uses a charcoal trap, a heater resistor and some plumbing to make a refrigerator that can be cycled to produce 0.4K for a day or so at a time. It makes many microwatts of 0.4K coldness from less than one watt of 4K coldness.

Unfortunately, the 3He leaked out and the gizmo is currently a paperweight since it was made by a very clever French guy who's no longer in the business.

You can still buy 3He refrigerators from other manufacturers, but they are two feet long. The 3He is available for several thousand dollars a bottle.

Re:0.35K is rather cold

[wass]

Getting to 4K is relatively easy, you get a dewar of helium (this is the relatively abundant He4 isotope) at roughly $4 per liter. You can cool to 1K relatively easily too by pumping on the vapor over the helium, evaporatively cooling ot down to 1K. It's inefficient to do this, though, people tend to build a 1K pot into their cryostat to only pump on a small volume of helium to cool their system to 1K, not the whole dewar.

Regarding the Helium 3 Fridge, that's actually doing the EXACT same thing as the 1K pot above, you're evaporatively pumping He3 with the charcoal sorb. Since He3 is rare and expensive, this is done in a closed system and recycled.

I know your pain, though, our He3 fridge has a leak, luckily not on the He3 system (He3 is super expensive), and it's been a pain in the ass to try to fix. To fix your system, you probably don't need that French dude to fix it, get a leak checker (find some experimental condensed matter guys that do vacuum sputtering or evaporation work, they'll have a leak checker), track down the leak on your He3 system, plug the leak (silver solder if possible w/ your machine shop), then pay some $$$ to inject some He3 back in when you're damn sure you've got no more leaks left.

Re:So.....

[Dunbal]

replacing nearly 10% of it with another element must mean that it falls into another classification.

      An alloy, if you will?

Re:So who the fuck cares

[swordgeek]

The only thing worse than an aggressively ignorant idiot is a foul-mouthed one.

In the 1830s, it was discovered that some materials acted as neither pure conductors nor pure insulators. They called them semiconductors, and they were a curiosity until the 1890s, when they were found to be useful as rectifiers and photovoltaic cells. Another 40 years later, and people started to consider them as a replacement for the triode vacuum tube, which was immensely useful but fragile and difficult to deal with.

Pure research in new directions isn't just allowed because it 'might lead to something,' it's absolutely essential in order to progress beyond refinement of the existing.

Re:OK, science is cool and everything

[RuBLed]

You forgot to put the link... http://www.twinkiesproject.com/

Re:So who the fuck cares

[agentcdog]

No. You are wrong. Read up about blackbody radiation. Space is like a big cavity with blackbody radiation that's about 3k. That's the thing about electromagnetic radiation - you don't need a medium. Let me make it clear... If you brought a piece of metal into space, would it keep cooling off by radiation? No. Why? Because at 3 kelvin space would be giving it as much energy as it is shedding. The pipe and space would be at an equilibrium state when the pipe reached 3 kelvin. You see how this is real temperature? Good.