Wednesday, June 23, 2010

Fermions or bosons?

In a "round table discussion" about the theory of the cuprate superconductors Patrick Lee suggested that the genuinely new idea that has been developed is:
"the notion of emergence of gauge fields and fractionalized particles as low-energy phenomena in systems that did not contain them in the starting model."
He suggests that this idea is of comparable importance in condensed matter theory to that of Goldstone bosons.

Gauge fields emerge when the electron or spin operators are represented in an alternative manner such as in terms of Schwinger bosons, slave fermions, slave bosons, or slave rotors. But a key question is for a given model Hamiltonian, which is the appropriate representation.
For quantum spin models it seems that which side of the Charles River you work on determines your preference for a particular representation. At Harvard, Subir Sachdev favours bosonic spinons, while on the opposite of the river, at MIT Patrick Lee favours fermionic spinons.

Where do the gauge fields come from?


  1. MIT and Harvard are the same side of the Charles. But it does wind a bit in between.

  2. I should have also added to my comment: thanks for all the posts. I've really enjoyed learning a bit of condensed matter physics here.