title: Critical exponents and scaling invariance in the absence of a critical point.
abstract: The paramagnetic-to-ferromagnetic phase transition is classified as a critical phenomenon due to the power-law behaviour shown by thermodynamic observables when the Curie point is approached. Here we report the observation of such a behaviour over extraordinarily many decades of suitable scaling variables in ultrathin Fe films, for certain ranges of temperature T and applied field B. This despite the fact that the underlying critical point is practically unreachable because protected by a phase with a modulated domain structure, induced by the dipole-dipole interaction. The modulated structure has a well-defined spatial period and is realized in a portion of the (T, B) plane that extends above the putative critical temperature, where thermodynamic quantities do not display any singularity. Our results imply that scaling behaviour of macroscopic observables is compatible with an avoided critical point.
authors.affiliation: Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
authors.forename: N
authors.initials: N
authors.lastname: Saratz
authors.affiliation: Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
authors.forename: D A
authors.initials: DA
authors.lastname: Zanin
authors.affiliation: Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Ramsperger
authors.affiliation: Facultad de Matemática, Astronomía y Física y Computacion, Universidad Nacional de Córdoba, Instituto de Física Enrique Gaviola (IFEG-CONICET), Ciudad Universitaria, 5000 Córdoba, Argentina.
authors.forename: S
authors.initials: S
authors.lastname: Cannas
authors.affiliation: Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule Zürich, and SIMDALEE2 Sources, Interaction with Matter, Detection and Analysis of Low Energy Electrons 2, Marie Sklodowska Curie FP7-PEOPLE-2013-ITN, CH-8093 Zürich, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Pescia
authors.affiliation: Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Vindigni