报告题目: High-symmetry quasicrystals: between ordered and random
报告人: Prof. Atahualpa S. Kraemer，National Autonomous University of Mexico
报告时间: 2023年11月17日星期五 10:00-10:50
报告地点: 物理科技楼101
报告邀请人: 施夏清
报告摘要: Quasicrystals are structures that, like crystals, have long-range order, i.e. their diffraction pattern is discrete, but like amorphous materials, they lack translational symmetry. This long-range order without translational symmetry is usually due to a forbidden rotational symmetry, such as 5- or 12-fold symmetries. As rotational symmetry increases, it is expected that the diffraction pattern becomes increasingly denser, and in some sense, the order of the system vanishes for short distances. To characterize this short-range order, we implement a new algorithm to produce quasiperiodic tilings with arbitrary symmetry far from the center of symmetry. Then we measure numerically the nearest neighbor distance distribution in a quasiperiodic tiling with high rotational symmetry and we compare these distributions with those obtained analytically on a random tiling, observing the same distributions in both cases. This result shows that the local structure of high-symmetry quasicrystals is indistinguishable from a random system. However, because of the long-range order, particles in a quasicrystal should be highly correlated for long distances. This opens the natural question: is there a characteristic length scale of quasicrystals at which the pair correlation function spikes? If it exists, is this length a function of the rotational symmetry? In this talk, I will show that this length scale exists, it depends on the rotational symmetry, and it is much shorter than expected, but still, it is large enough to observe some properties of disordered systems for high-symmetry quasicrystals.
报告人简介: Atahualpa S. Kraemer studied physics at the Faculty of Sciences of the National Autonomous University of Mexico (UNAM), where he also obtained his Ph.D. in Physics under the supervision of David P. Sanders, graduating in 2014. That same year he began his postdoc in Düsseldorf, Germany working in the group of Michael Schmiedeberg, a postdoc that continued in Erlangen, Germany until July 2016. In August 2016 he got a position as an associate professor at UNAM in the area of statistical physics where he currently works. His research areas are colloids, glasses, jammed systems, and quasicrystals. In 2022 he was promoted to full professor, and recently he was nominated for the award “National University Distinction Recognition for Young Academics in the area of Research in Exact Sciences 2023” at UNAM.
