Strain-mediated phase coexistence in heteroepitaxial films

We present experimental evidence of the equilibrium coexistence between crystalline phases in heteroepitaxial films of MnAs on GaAs. The phases, which can coexist in the bulk system only at one temperature point, coexist in the epitaxial film over a wide temperature interval. An apparent contradiction with the Gibbs phase rule is resolved by the presence of strain in the film.