1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Landau theory: why does a m^3 term implies first order transition phase

  1. Dec 7, 2011 #1
    Hi,

    I am not sure it is the right subcategory to post a question on statistical physics. But anyway, I read a couple of times that adding a m^3 to the Landau free energy implies that we may observe a first order transition phase, but I don't see why. Maybe it does imply some discontinuity in the entropy, latent heat, but I am not seeing that.
     
  2. jcsd
  3. Dec 8, 2011 #2

    DrDu

    User Avatar
    Science Advisor

    What is m? Mass, magnetic moment?
     
  4. Dec 10, 2011 #3
    M is the magnetic moment, the order parameter.
     
  5. Dec 11, 2011 #4
    Try to make a plot of a sample free energy:
    [itex]F=t m^2 + b m^3 + m^4[/itex]
    for different values of t and b? In particular, try a fixed t at some finite value and varies b.

    When t >> b, the free energy is minimum is at m=0, then as you increase b, at some point, the minimum JUMPS from 0 to some finite value. That, by definition, is a first order transition where the order parameter has a discontinuous jump.
     
  6. Dec 13, 2011 #5
    Thanks, you made it clear ;)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Landau theory: why does a m^3 term implies first order transition phase
Loading...