Landau order parameter and mean-field transition
Research context
postgraduate concept · conditional · As of 2026-10-10
For a uniform dimensionless scalar order parameter m with symmetry m↦−m, an effective free-energy density f=f₀+a m²/2+b m⁴/4 has minima m=0 for a>0 and m²=−a/b for a<0 when b>0.
Key knowledge
For a uniform dimensionless scalar order parameter m with symmetry m↦−m, an effective free-energy density f=f₀+a m²/2+b m⁴/4 has minima m=0 for a>0 and m²=−a/b for a<0 when b>0. This is a small-m mean-field model; thermodynamic-limit nonanalyticity and fluctuation effects require separate treatment.
Values and equations
f−f₀=a m²/2+b m⁴/4; m₀²=−a/b (a<0)
- f,f₀,a,b
- Free-energy density and coefficients for dimensionless m J m⁻³
- m,m₀
- Dimensionless order parameter and equilibrium magnitude
Conditions and scope
- Near a continuous transition with the stated symmetry, stable b>0 and negligible higher powers in the selected range.
- The coefficients are material/model dependent. A negative quartic term needs stabilizing higher orders and can yield a first-order transition; the quartic model is not universal.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Inspected §§1.2–1.3: small order parameter, stable quartic potential and limits of mean field; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication.
2026-10-10 · Author source inspection of the displayed claim, model assumptions and equations; independent exact-content and branch-inventory review is a separate gate. Contemporary status is a dated snapshot, not a promise of ongoing monitoring.
Entry details
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- research-physics-landau-order-parameter
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference