Landau Theory of Phase Transitions: Order Parameter Expansion and Free Energy Diagrams

2018 ◽  
pp. 291-300
Author(s):  
Biman Bagchi
Keyword(s):  
Free Energy ◽  
Phase Transitions ◽  
Order Parameter ◽  
Landau Theory ◽  
Parameter Expansion

Phase Diagrams for Incommensurate Systems

1982 ◽  
Vol 21 ◽  
Author(s):  
P. Toledano
Keyword(s):  
Free Energy ◽  
Phase Transitions ◽  
Energy Density ◽  
Phase Diagrams ◽  
Order Parameter ◽  
Landau Theory ◽  
Free Energy Density ◽  
Lock In

ABSTRACTPhase diagrams, for systems undergoing one or several incommensurate and lock-in transitions, are discussed in the framework of the Landau theory of phase transitions. It is shown that their essential features can be deduced from the explicit forms of the free-energy density ø and the k-dispersion of the coefficient α(→k)of the quadratic contribution of the order-parameter components in ø. Two families of phase diagrams are distinguished depending on symmetry considerations.

scholarly journals Multi-mode excitation drives disorder during the ultrafast melting of a C4-symmetry-broken phase

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Daniel Perez-Salinas ◽  
Allan S. Johnson ◽  
Dharmalingam Prabhakaran ◽  
Simon Wall
Keyword(s):  
Phase Transitions ◽  
Order Parameter ◽  
Landau Theory ◽  
Mean Field ◽  
Atomic Scale ◽  
Time Dependent ◽  
Ginzburg Landau ◽  
Mode Excitation ◽  
The Mean ◽  
Multi Mode

AbstractSpontaneous C4-symmetry breaking phases are ubiquitous in layered quantum materials, and often compete with other phases such as superconductivity. Preferential suppression of the symmetry broken phases by light has been used to explain non-equilibrium light induced superconductivity, metallicity, and the creation of metastable states. Key to understanding how these phases emerge is understanding how C4 symmetry is restored. A leading approach is based on time-dependent Ginzburg-Landau theory, which explains the coherence response seen in many systems. However, we show that, for the case of the single layered manganite La0.5Sr1.5MnO4, the theory fails. Instead, we find an ultrafast inhomogeneous disordering transition in which the mean-field order parameter no longer reflects the atomic-scale state of the system. Our results suggest that disorder may be common to light-induced phase transitions, and methods beyond the mean-field are necessary for understanding and manipulating photoinduced phases.

Phase Diagrams of Ni2MnX (X = In, Sn, Sb) Heusler Alloys with Inversion of Exchange Interaction

2008 ◽  
Vol 583 ◽  
pp. 131-146 ◽  
Author(s):  
Vasiliy D. Buchelnikov ◽  
Sergey Taskaev ◽  
M.A. Zagrebin ◽  
Peter Entel
Keyword(s):  
Free Energy ◽  
Phase Transitions ◽  
Exchange Interaction ◽  
Phase Diagrams ◽  
Magnetic Phase ◽  
Landau Theory ◽  
Heusler Alloys ◽  
Magnetic Phase Transitions ◽  
Experimental Phase ◽  
Ginzburg Landau

In this work with the help of the phenomenological Ginzburg-Landau theory of structural and magnetic phase transitions the phase diagrams of Heusler Ni-Mn-X (X = In, Sn, Sb) alloys with the inversion of exchange interaction are investigated. The investigation shows that the type of the phase diagrams in Heusler Ni-Mn-X (X = In, Sn, Sb) alloys depends on the value and sign of the free energy parameters. As it is seen from the analysis of the phase diagrams with the determined values and signs of the parameters of Landau functional there are thermodynamic paths which allow to explain experimental phase transitions in Heusler alloys Ni-Mn-X (X = In, Sn, Sb) and Ni-Co- Mn-X (X = In, Sn, Sb) qualitatively.

scholarly journals Fluctuation effects in metastable states near first-order phase transitions

2016 ◽  
Vol 30 (21) ◽  
pp. 1650149
Author(s):  
Dimo I. Uzunov
Keyword(s):  
Free Energy ◽  
Perturbation Theory ◽  
Phase Transitions ◽  
Internal Energy ◽  
Order Parameter ◽  
First Order ◽  
Pressure Concentration ◽  
Fluctuation Effects ◽  
First Order Phase ◽  
Temperature Factors

Fluctuation effects at first-order phase transitions driven by changes of other-than-temperature factors like pressure, concentration or external fields are investigated by perturbation theory. The results for the fluctuation contributions to the order parameter, the internal energy and the free energy at pre-transitional states near spinodal points of first-order phase transitions are presented to the first-nonvanishing order of the expansion parameters of the theory.

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