title: Experimental observation of defect pair separation triggering phase transitions.
abstract: First-order phase transitions typically exhibit a significant hysteresis resulting for instance in boiling retardation and supercooling. The hysteresis arises, because nucleation of the new phase is activated. The free-energy change is positive until the nucleus reaches a critical size beyond which further growth is downhill. In practice, the barrier is often circumvented by the presence of heterogeneous nucleation centres, e.g. at vessel walls or seed crystals. Recently, it has been proposed that the homogeneous melting of ice proceeds via separation of defect pairs with a substantially smaller barrier as compared to the mere aggregation of defects. Here we report the observation of an analogous mechanism catalysing a two-dimensional homogeneous phase transition. A similar process is believed to occur in spin systems. This suggests that separation of defect pairs is a common trigger for phase transitions. Partially circumventing the activation barrier it reduces the hysteresis and may promote fluctuations within a temperature range increasing with decreasing dimensionality.
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 82, 6020 Innsbruck, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Cordin
authors.affiliation: 1] Institute of Physical Chemistry, University of Innsbruck, Innrain 82, 6020 Innsbruck, Austria [2].
authors.forename: B A J
authors.initials: BA
authors.lastname: Lechner
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 82, 6020 Innsbruck, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Duerrbeck
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 82, 6020 Innsbruck, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Menzel
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 82, 6020 Innsbruck, Austria.
authors.forename: E
authors.initials: E
authors.lastname: Bertel
authors.affiliation: Institute of Applied Physics, Vienna University of Technology, Gusshausstr. 25/134, 1040 Vienna, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Redinger
authors.affiliation: Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Vienna, Austria.
authors.forename: C
authors.initials: C
authors.lastname: Franchini