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Physical review. B, Condensed matter

Tricritical behavior in a two-dimensional field theory

Herbert W. Hamber

Published May 1, 1980• 15 citations
Publisher

Abstract

The critical behavior of a two-dimensional scalar Euclidean field theory with a potential term that allows for three minima is analyzed using an approximate position-space renormalization-group transformation on the equivalent quantum spin Hamiltonian. The global phase diagram shows a tricritical point separating a critical line from a line of first-order transitions. Other critical properties are examined, and good agreement is found with results on classical spin models belonging to the same universality class.

DOI
10.1103/physrevb.21.3999

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The critical behavior of a two-dimensional scalar Euclidean field theory with a potential term that allows for three minima is analyzed using an approximate position-space renormalization-group transformation on the equivalent quantum spin Hamiltonian. The global phase diagram shows a tricritical point separating a critical line from a line of first-order transitions. Other critical properties are examined, and good agreement is found with results on classical spin models belonging to the same universality class.
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The critical behavior of many physical systems involves two competing n1- and n2-component order-parameters, S1 and S2, respectively, with n = n1 + n2. Varying an external control parameter g, one encounters ordering of S1 below a critical (second-order) line for g < 0 and of S2 below another critical line for g > 0. These two ordered phases are separated by a first-order line, which meets the above critical lines at a bicritical point, or by an intermediate (mixed) phase, bounded by two critical lines, which meet the above critical lines at a tetracritical point. For n = 1 + 2 = 3, the critical behavior around the (bi- or tetra-) multicritical point either belongs to the universality class of a non-rotationally invariant (cubic or biconical) fixed point, or it has a fluctuation driven first-order transition. These asymptotic behaviors arise only very close to the transitions. We present accurate renormalization-group flow trajectories yielding the effective crossover exponents near multicriticality.
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