Reaching Absolute Zero: Methods to Achieve Superconductors

[Kalrag]

I hear how people create superconductors by taking a metal and freezing it to Absolute Zero(0 Kelvin). What are some methods to get this sort of tempuature? Can anyone help?

 

[jambaugh]

Not all the way to T=0, just relatively close (near or less than 10Kelvin until the new higher temp superconductors were discovered.)

One of the commonly used commercial superconductors is a Lead Telluride alloy and to cool it sufficiently one uses liquid helium which has a boiling point (4.2K) below the critical temperature.

I suggest you start by reading the wikipedia article on the history of superconductivity.

 

[K^2]

There are high temperature superconductors that operate at liquid nitrogen temperatures. It's still pretty cold, but nowhere even close to absolute zero.

 

[Kalrag]

I know but how do they get "near" absolute Zero? Like what are the methods.

 

[Feldoh]

Perhaps this might help: http://www.pbs.org/wgbh/nova/zero/program.html

 

[NobodySpecial]

I know but how do they get "near" absolute Zero? Like what are the methods.

Down to around 4k you can just use liquid gases (Helium boils at 4Kelvin)

Below that you just use a refrigerator.
It's basically the same principle as your kitchen fridge:
1, you compress a fluid it gets hot - you extract the heat
2, you expand the fluid it takes in heat and cools the target
The only difference is that the 'hot' side is already cooled to 4 Kelvin

I think the record lowest temperature is probably a magnetic fridge.
Still the same concept, magnetizing a piece of material causes it to heat up - taking heat in from the surroundings , you take it out of the magnetic field and it cools down giving off that heat which you then extract.

 

[K^2]

Lowest temperatures are achieved various laser-cooling methods, but these only work on gas/plasma caught in magnetic traps.

Usually, for sub-4K temperatures they lower pressure to force Helium to boil at a lower temperature. This will let you get down to a little less than 1K.

 

[Mindscrape]

I think the record lowest temperature is probably a magnetic fridge.
Still the same concept, magnetizing a piece of material causes it to heat up - taking heat in from the surroundings , you take it out of the magnetic field and it cools down giving off that heat which you then extract.

Huh? Are you referring to negative kelvin? If so, I guess that while negative kelvin would mathematically be lowest record temperature, in that a negative numbers are less than positive numbers, negative kelvin temperatures are actually "hotter" than positive temperatures.

 

[NobodySpecial]

In think you replied to the wrong post, and I'm guessing k^2 meant sub_hyphen_4k not -4k

 

[f95toli]

No, he is referring to adiabatic demagnetization refrigeration (ADR). It is basically a method for cooling things by playing with magnetic fields. It can either be used on its own to e.g. cool something from about 4K (liquid helium) to around 40 mK(=0.04K) or so . Or, you can bolt a ADR to the bottom of a dilution refrigerator, the latter can cool even a large mass down to about 20mK or so and keep it there indefinitly (as long as the pumps are running), then you start your ADR which cools everything down to about a 1mK or so.
This is how you cool macroscopic objects down to very low temperatures.

 

[luriol]

Although, you can get even closer to absolute zero (around 1 billionth of a degree) using optical cooling. See for example http://www.eurekalert.org/pub_releases/2003-09/miot-mta090903.php

 

[Andy Resnick]

f95toli's post here:

https://www.physicsforums.com/showpost.php?p=2405957&postcount=20

had some really interesting points to consider, regarding this discussion- at very low temperatures, it's nontrivial to *define* a temperature.