Tetracritical point

Little is known about higher order critical points. Tetracritical points, at least imsynnnetrical ones, require four components. However for tetracritical points, the crossover dimension mean-field, or at least analytic. 

The first two of these are tetracritical points, and the third point is an even higher order multicritical point ( pentacritical). 

Fig. 29. Superconducting B-T phase diagram as obtained from thermal expansion and magnetostriction (van Dijk et al., 1993 van Dijk, 1994). Critical field curves cross at a tetracritical point which is present for all field directions, therefore three distinct SC phases A(1,0), and C(0,1) with...

The minimum in the ferromagnetic transition temperatures at H0...0, 25Er,o.75Rh4B4 was identified as a decoupled tetracritical point by Maekawa and Huang (1980). 

Corrales, L.R., Wheeler, J.C. Tetracritical and novel tricritical points in sulfur solutions A Flory model for polymerization of rings and chains in solvent. J. Chem. Phys. 1989, 90, 5030. 

The description of the Chen-Lubensky model is reasonably well borne out by experiment [50,51] the universal topology of the phase diagram and the existence of a Cx=0 line in particular are well established. An interesting possibility pointed out by Grinstein and Toner [52] with a model of dislocation unbinding is the existence of a biaxial nematic phase if the N-SmA and SmA-SmC lines are second order with XT critical exponents, the N-SmA-SmC point should be tetracritical [53] and a mixed phase (i.e. a biaxial nematic) should show up. It has however not been observed so far. 

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