# Superconductivity in the Presence of a Magnetic Field

1. Apr 27, 2015

### korneld

Curious: say, it takes a particular piece of superconductive material "x" seconds to reach the state when submerged in liquid nitrogen. Now, say we try to do the same in presence of a (strong) magnetic field. Does x increase, decrease or does it stay the same?

My money is on increasing, because it has to do work to exclude the magnetic field. Am I wrong?

2. Apr 27, 2015

### Alex299792458

I haven't done much research but from what I know a superconductor has 0 Ω so there is no delay from point a to point b. So if you add a magnetic field it doesn't matter if it's strong or weak it will still have 0 Ω, you can't have -Ω because 0 Ω is the furthest your going to get in conductivity. You might see x decrees when the superconductor is submerged in liquid nitrogen and x being increased in any magnetic field not due to the effects of the 2 conditions but because the liquid nitrogen is very (VERY) cold so it will stay in superconductivity but if it's in any magnetic field there is nothing making it cooler so it heats up above the critical point for superconductivity and no longer has 0 Ω.

PS. Are you asking about a type ll superconductor or type l?

3. Apr 27, 2015

### Alex299792458

But for moment I wouldn't say your right or wrong.

4. Apr 27, 2015

### king vitamin

An external magnetic field will decrease the temperature at which the superconducting transition occurs, so it will take longer for the material to superconduct (assuming you're starting at the same temperature and the critical temperature is still above the temperature of liquid nitrogen).

5. Apr 28, 2015

### Staff: Mentor

The resistance is not related to the original question, but it is not true: the critical temperature depends on the external magnetic field and resistance depends on the critical temperature (above: resistance, below: no resistance)
Liquid nitrogen at its boiling point is hot for most superconductors.

@korneld: see king vitamin's post, with a magnetic field it will take longer as it has to get colder.

6. Apr 28, 2015

### Alex299792458

In the case of a type ll superconductor of Yttrium Barium Copper Oxide(YBaCuO) people always use liquid nitrogen to cool it down because it has a very high temperature conductivity and by very high I like one of the highest temperature out of all superconductors with a whooping conductivity point of 90 kelvin and liquid nitrogen(N) is 77 kelvin, well nitrogen's boiling point is 77 kelvin but it can go lower but 77 kelvin is the hottest it gets there are other superconductors with higher temperatures like Mercury Barium Calcium Copper Oxide(HgBaCaCuO) with a outstanding superconductivity temperature of 134 kelvin there are other arrangements for high superconductivity temperatures like Strontium(Sr) or Titanium(Ti) which all have high superconductivity points because they have Copper(Cu) and Oxygen(O) together in the mix but the most common high temperature superconductivity point is Yttrium Barium Copper Oxide (or YBCO for short) which is really cheap and easy to get so they use it and also liquid nitrogen is also the cheapest but also the hottest liquid gas you can get and that's why combined with a high critical temperature YBCO makes a really cheap and efficient superconductor and yes I have did it before and when I placed it into a magnetic field of a neodymium(Nd) magnet it floated, well it's called quantum levitation and it's quantum locked but it looks like it's floating. You can watch some youtube videos about it link: to learn more. It works better with higher magnetic flux densities like neodymium(Nd) magnets. Also YBCO is speacil in it's own way all other high critical temperature crystals have a crystal structure of a teragonal but YBCO is orthorhombic.