dualtransition

Dualtransition is a term used in physics and materials science to describe systems that display two distinct phase transitions as a single control parameter, typically temperature, is varied. It can refer to two separate changes in order parameters, an intermediate phase, or two closely spaced transitions that are coupled by interactions within the material.

A common theoretical approach uses two order parameters, φ and ψ, with a Landau-type free energy F = a1(T)φ^2 + b1φ^4 + a2(T)ψ^2 + b2ψ^4 + γφ^2ψ^2. As temperature changes, a1 and a2 change sign, producing Tc1 and Tc2. Depending on the coupling γ and higher‑order terms, the transitions may be sequential, form an intermediate phase, or merge into a single multicritical event. Phase diagrams can include bicritical or tetracritical points.

Experimentally, dual transitions appear as two anomalies in heat capacity or susceptibility, two sets of structural or magnetic changes, or two distinct transport regimes. Resolving true dual transitions from broad crossovers or sample inhomogeneity requires high-resolution measurements and, often, measurements under pressure or chemical tuning.

Dualtransition concepts are relevant for strongly correlated and ferroic systems, multiferroics, and engineered materials where coupled order parameters govern functional properties such as conductivity, magnetism, or dielectric response.

See also: phase transition, order parameter, Landau theory, multicritical point, coupled order parameters.