Invited

Quasicrystals and approximants in two-dimensional perovskite oxides

S. Förster¹, and W. Widdra ^1,2

¹Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany

²Max-Planck-Institut für Mikrostruktruphysik, Halle, Germany

When approaching the two-dimensional limit, oxides are known to exhibit strong variations in their structures and properties as compared to the respective bulk materials [1]. One of the extreme examples are the two-dimensional oxide quasicrystals (OQCs), which have been discovered for reduced perovskite oxides at the Pt(111) interface [2, 3]. OQCs have been reported for BaTiO₃ and more recently also for SrTiO₃. Furthermore, approximant structures have been observed, in which selected motifs of the OQC are periodically repeated. In Figure 1a an example of a simple approximant structures is given, which has been observed for BaTiO₃ [4]. The more complex approximant structure shown in Fig. 1b has been reported for SrTiO₃ [3]. The later is almost indistinguishable from the aperiodic structure in an diffraction experiment. Our studies unravel OQCs as best-controlled QC model systems for addressing the fundamental questions related to the driving forces for aperiodic structure formation.

Figure 1: Comparison of periodic approximant tilings (a, b) and the aperiodic Stampfli-Gähler tiling as observed for OQCs (c). The OQC tiling lacks translational symmetry.

[1] F. Netzer, S. Fortunelli (eds), Oxide Materials at the two-dimensional limit, Springer (2016).

[2] S. Förster, K. Meinel, R. Hammer, M. Trautmann, W. Widdra, Nature 502, 215 (2013).

[3] S. Schenk et al., J. Phys.: Condens. Matt. doi.org/10.1088/1361-648X/aa5bdb (2017).

[4] S. Förster et al., Phys. Rev. Lett. 117, 095501 (2016).