title: Continuous melting through a hexatic phase in confined bilayer water.
abstract: Liquid water is not only of obvious importance but also extremely intriguing, displaying many anomalies that still challenge our understanding of such an a priori simple system. The same is true when looking at nanoconfined water: The liquid between constituents in a cell is confined to such dimensions, and there is already evidence that such water can behave very differently from its bulk counterpart. A striking finding has been reported from computer simulations for two-dimensionally confined water: The liquid displays continuous or discontinuous melting depending on its density. In order to understand this behavior, we have analyzed the melting exhibited by a bilayer of nanoconfined water by means of molecular dynamics simulations. At high density we observe the continuous melting to be related to the phase change of the oxygens only, with the hydrogens remaining liquidlike throughout. Moreover, we find an intermediate hexatic phase for the oxygens between the liquid and a triangular solid ice phase, following the Kosterlitz-Thouless-Halperin-Nelson-Young theory for two-dimensional melting. The liquid itself tends to maintain the local structure of the triangular ice, with its two layers being strongly correlated yet with very slow exchange of matter. The decoupling in the behavior of the oxygens and hydrogens gives rise to a regime in which the complexity of water seems to disappear, resulting in what resembles a simple monoatomic liquid. This intrinsic tendency of our simulated water may be useful for understanding novel behaviors in other confined and interfacial water systems.
authors.affiliation: CIC nanoGUNE, 20018 Donostia-San Sebastián, Spain.
authors.forename: Jon
authors.initials: J
authors.lastname: Zubeltzu
authors.affiliation: CIC nanoGUNE, 20018 Donostia-San Sebastián, Spain.|Department of Materials and the Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: Fabiano
authors.initials: F
authors.lastname: Corsetti
authors.affiliation: Physics and Astronomy Department, SUNY Stony Brook University, New York 11794-3800, USA.
authors.forename: M V
authors.initials: MV
authors.lastname: Fernández-Serra
authors.affiliation: CIC nanoGUNE, 20018 Donostia-San Sebastián, Spain.|Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.|Basque Foundation for Science Ikerbasque, 48011 Bilbao, Spain.|Donostia International Physics Center, 20018 Donostia-San Sebastián, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Artacho