What Technologies are Used to Measure Near 0 K Temperatures?

[sniffer]

1. why, instead of cooper pair, don't we have a group of N electrons coupled for superconductivity?

2. Has cooper pair been observed experimentally?

3. What kind of thermometer do we used to measure near 0 K temperature?

4. Has Josephson tuneling for oxyde high Tc been made? Because there was a paper (I think from Bell's Lab) which claimed so? What is the potential technology to make a few angstrom thick of insulator?

thank you.

 

[ZapperZ]

1. why, instead of cooper pair, don't we have a group of N electrons coupled for superconductivity?

(a) if N is odd, how do you form a composite boson?

(b) the phase space for such thing to occur (remember that each electron within the cooper pair continuously scatter in and out of the momentum space configuration that you need to be "luckly" to get N=4 electrons that happen to pair up in the right configuration at a particular time) is so exceedingly small even at T=0 that it is very unlikely to happen.

2. Has cooper pair been observed experimentally?

You'd better believe it. How else do you explain the energy gap in the single-particle spectrum seen in ARPES and tunneling measurements? Furthermore, the basic charge measured in SQUID measurement is 2e, not e.

3. What kind of thermometer do we used to measure near 0 K temperature?

Either a rather complex "thermocouple", or by using statistical distribution of the cold material itself.

4. Has Josephson tuneling for oxyde high Tc been made? Because there was a paper (I think from Bell's Lab) which claimed so? What is the potential technology to make a few angstrom thick of insulator?

thank you.

Next time when you decide to bring up a source, make sure you have an exact citation. Bringing it up like this is almost pointless since you have something in mind, but I don't get to see it clearly. Furthermore, you might be citing the already-discredited Schon papers. Without an exact references, can you see how impossible it is to address such a thing?

Josephson tunneling in high Tc superconductors has been done many times (I have done it myself). The magnitude of the supercurrent has also been shown to follow the Ambegaokar-Baratov relationship quite well.

Zz.

 

[Gokul43201]

More on 3 : Temperatures in the range of a 0.1K to 10K are accurately measured by resistance (often Germanium) and capacitance (if measuring in the presence of B-fields) thermometers.

PS : Another excellent way to measure temperatures from 5K down to 0.5K is with vapor pressure thermometers.