# What is Order parameter: Definition and 15 Discussions

In chemistry, thermodynamics, and many other related fields, phase transitions (or phase changes) are the physical processes of transition between the basic states of matter: solid, liquid, and gas, as well as plasma in rare cases.
A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change, often discontinuously, as a result of the change of external conditions, such as temperature, pressure, or others. For example, a liquid may become gas upon heating to the boiling point, resulting in an abrupt change in volume. The measurement of the external conditions at which the transformation occurs is termed the phase transition. Phase transitions commonly occur in nature and are used today in many technologies.

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1. ### I Understanding the Derivation of the Ginzburg Criterion for the Ising Model

For the Ising Model, the Ginzburg Criterion is, for ##m_{0}## the order parameter and ##\delta m## the fluctuations: $$\langle\delta m\left(x\right)\delta m\left(x^{\prime}\right)\rangle << m_{0}^{2}$$. I want to understand how to derive the left hand side of the inequality from ##\langle M^{2}...
2. ### A Order parameter, symmetry breaking Landau style

Hi all, I am somewhat familiar the Landau Ginzburg paradigm for phase transition. My understanding is that it is a phenomological model of 2nd order phase transitions by "guessing" that the free energy can be expanded a configuration integral (path integral) of a functional of a local order...
3. ### Landau Theory - Order parameter- Extensive or intensive?

Homework Statement [/B] 1) Is the order paramter ##\phi(x)## intensive or extensive? 2) Is ##M## intensive or extensive? With the following definitions : Homework Equations The Attempt at a Solution 1) Free energy is extensive, however I don' think I can use this to deduce whether...
4. ### The difference between order parameter and state parameter?

At first, we need some state parameters(like P/T/V) to fully describe a system. And the order parameter is also a parameter which could describe the property of the system. However, in the Laudau theory, why it said that order parameter is an external parameter(not a independent variable)? Is...
5. ### Stress tensor from action in Landau-Ginzburg field theory

I would appreciate any help with the following question: I know that for relativistic field theories, the stress tensor can be obtained from the classical action by differentiating with respect to the metric, as is explained on the wikipedia page...
6. ### Order Parameter in a Gauge Theory, Can we find one in a Gauge Theory(like QCD)?

Hello Community! I can't find a good answer(if there is) to my question. When in statistical mechanics we can define the order parameter for to study some phase transition. we need to define a order parameter. Now, I want to know if we can to define/find some "order parameter" for to...
7. ### Orienational order parameter in isotropic systems

Hi everyone, I have what may be a dummy question. In NMR or in the study of liquid crystals for example, an order parameter S is often used: S=\left\langle\frac{1}{2}\left(3\cos^{2}\theta-1\right)\right\rangle with \theta the angle of the molecule with a "director" (the magnetic field in...
8. ### Order parameter in quasicrystals

What's the order parameter in quasi crystals? Only the broken rotational symmetry?
9. ### Introduction to order parameter fields

Hi folks, I'm taking a class in statistical mechanics out of Sethna's text. Part of the course involves student presentations. I've settled on his chapter on order parameters, broken symmetry and topology. Its a relatively short chapter and I'd like to read some more. I'm looking for...
10. ### About the order parameter in antiferromagnetism

Hello everyone, As is known to all, the order parameter for the ferromagnetic case in the Landau expression is chosen as the magnetization. This is easy to understand. But for the antiferromagnetic case, what is the order parameter? People told me it was magnetic moment on the sublattice. But...
11. ### Stat mech problem on order parameter

Homework Statement A system has a two component order parameter: [phi1, phi2]. The mean-field Landau free energy is E(\phi_1,\phi_2) = E0+at(\phi_1^2+\phi_2^2)+b(\phi_1^2+\phi_2^2)^2+c(\phi_1^4+\phi_2^4) where t, a, and b are positive constants. Represent the order paramter as a vector on...
12. ### Order parameter, correlation function and length

Hello people, I don't understand the relation between those concepts, I tried to read what's written in wikipedia about them but no use. Can someone please elaborate more about the relation between them in some intuitive manner? Thank you :)
13. ### What is order parameter and how to find critical temperature?

I am reading some material on phase transition. In those, they use order parameter quite a lot, but what is order parameter? What's the physical significance of it? If I got the free energy , which involving order parameter m, how can I find the critical temperature?
14. ### Order parameter of charge density wave in one dimension

In one dimensional electron gas in charge density wave phase, as I know , the density of electrons will be periodic. The order parameter of charge density wave is written as O_{CDW}(x)=\sum_s\psi_{L,s}^{\dagger}(x)\psi_{R,s}(x) For Luttinger model, the \psi is the Fermion annihilation field...
15. ### Order parameter in BCS Theory

Hi guys, What exactly is an order parameter? What does the order parameter in BCS Theory represent? I can't find anything on this anywhere. Thanks in advance Tom