- #1
maverick_starstrider
- 1,119
- 6
Alright, here is something that is driving me insane. I feel like I've looked through every stat mech book on the planet and not a one discusses this stuff properly. My difficulty is in the study of phase transitions when one applies Landau's approach of expanding the free energy about the order parameter at the critical point. If one then assume that the order parameter fluctuates in space Landau originally added a term of the form gradient(M) dot gradient(M) and simply said something like "this is the simplest spatial derivative that respects the relevant symmetries". My question is this, what is the GENERAL spatial expansion about the critical point? I've never seen a series expansion that had a term like gradient(M) dot gradient(M) (maybe I missed that day in vector calc), what are the lower order terms? what are the higher order terms? Why do they go to zero/become negligible?
What I would really like is an explanation/discussion of how one in general forms a series expansion in space about the critical point and then a discussion of why all but a gradient(M) dot gradient(M) term can be neglected. And I don't want to really get my hopes up but a discussion of how accurate the spatial expansion is in general and when it is not so valid (when an expansion in space isn't valid, not the ginzburg criterion) would be amazing. Anyway, if someone could point me to a source that actually discusses in detail this non-trivial series expansion (or just explain it here) rather than plopping down gradient(M) dot gradient(M) and saying "well here's what Landau used and he knew his stuff" that would be amazing. Thanks in advance.
P.S. I've already been through Reichl, Huang, Pathria, Cardy and Kadanoff (and Landau obviously who started the whole thing by plopping down a term with a sentences justification). Not a one does it.
What I would really like is an explanation/discussion of how one in general forms a series expansion in space about the critical point and then a discussion of why all but a gradient(M) dot gradient(M) term can be neglected. And I don't want to really get my hopes up but a discussion of how accurate the spatial expansion is in general and when it is not so valid (when an expansion in space isn't valid, not the ginzburg criterion) would be amazing. Anyway, if someone could point me to a source that actually discusses in detail this non-trivial series expansion (or just explain it here) rather than plopping down gradient(M) dot gradient(M) and saying "well here's what Landau used and he knew his stuff" that would be amazing. Thanks in advance.
P.S. I've already been through Reichl, Huang, Pathria, Cardy and Kadanoff (and Landau obviously who started the whole thing by plopping down a term with a sentences justification). Not a one does it.