What Is a Fermionic Condensate?

[mark1]

http://news.bbc.co.uk/2/hi/science/nature/3441643.stm

 

[pallidin]

Read that earlier on CNN.com as well.
Fascinating! Does physics rock the world or what!

 

[adrenaline]

Don't laugh, I am very ignorant but what is the difference (as explained to a moron like me) between this and the Bose Einstein condensate? (Please, no chuckeling).

 

[chroot]

All particles belong to one of two camps: the bosons live on one side of the tracks, and the fermions on the other.

If you open up an auditorium to a waiting crowd of fermions, they will file in in an orderly fashion, filling up the first row before beginning to fill up the second row, and so on in proper grade-school fashion. No two fermions are allowed to share the same seat -- the same quantum-mechanical state.

If you open up the auditorium to a crowd of rowdy bosons, however, the result will be very different. Bosons have no personal-space issues; not only are they able to share the same quantum state, they actually pursue it. The throng of bosons will eagerly seek to pile up on top of one another in the middle of the stage as soon as possible.

The utility of such a boson-pile to physicists is that it does en masse the same weird quantum mechanical things that bosons do all the time in isolation. It's difficult to observe just one boson, but very easy to observe a whole bucketful. When you supercool liquid helium-4 (each atom of which is a boson), you open the auditorium door and give the atoms a chance to pile up on stage. The phase transition that occurs as all the atoms enter the same quantum state is called condensation, or, more specifically, Bose-Einstein condensation. A bucketful of supercold liquid helium displays funky quantum-mechanical behavior at scales visible to human eyes. Bose-Einstein condensates flow without viscosity through the tiniest pores, and they creep up the side of containers in thin films. When you spin their container, they stubbornly choose to rotate at only certain discrete velocities, bucking common sense.

A fermionic condensate, as you might now expect, is the result of supercooling a fermionic substance. These space-conscious particles don't undergo a sudden phase transition like their amicable cousins, but they do condense in their own way.

Imagine again the auditorium buzzing with energetic fermions. There are precisely as many seats as fermions, but it's warm in there and no one wants to sit still. Some are walking in the aisles, others are buying nachos, and others are loitering in the street outside. Seats go unused, energy levels unfilled. As the temperature falls, the restless fermions succumb, and begin to fill in their seats and stay put. Below some critical temperature, not even the fermion nearest the door has the inclination to leave. Below this temperature, the fermions are said to be condensed -- locked rigidly in their energy levels, packed as tightly in their seats as they can be packed.

While not as spectacular as Bose-Einstein condensation, fermionic condensation holds its own surprises. The one on most physicists' minds is a process known as "Cooper pairing," by which two fermions can team up to put on a boson act. The behavior of these pairs, disguised as cozy bosons among hordes of aloof fermionic brethren, is the cause of important phenomena like superconductivity. Electrons are fermions, and only when they form Cooper pairs can they conduct electricity without resistance. The electrons in a superconductor are, in fact, one form of a fermionic condensate.

Here's a good article from Physics Today:

http://www.physicstoday.org/vol-56/iss-10/pdf/vol52no10p17-18.pdf

- Warren

 

[adrenaline]

Thankyou for such a wonderfully crafted reply! Even my feeble mind now has some inkling of what this stuff is all about. Thanks!

 

[jimmy p]

...uh, i may have missed the name completely, but what is this new form of matter called?

 

[chroot]

Fermionic condensate.

- Warren