From Phonons to Phasons – Ultrafast Atomic Vibrations in Quasicrystals

• Applicant: Dr. Yoav William Windsor
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553382698

Quasicrystals are solids with “perfect” long-range atomic order, but without the long-range periodicity that conventional crystals possess. Their aperiodicity allows quasicrystals to harbor “phasons”, quasiparticles of atomic vibrations that are distinct from phonons. Phasons have recently demonstrated super-sonic velocities, suggesting a new route for rapid thermal transport. This may serve as a fundamentally new approach to improving efficiency and heat management in nanoelectronics, which is of great environmental importance. The aim of this project is to study the femtosecond evolution of atomic vibrations in quasicrystals, in particular “phasons” and their ultrafast interactions with phonons and charge carriers. The experimental hallmark of quasicrystals is the existence of symmetries that are incompatible with a Bravais lattice. The most notable example is that of 5- and 10-fold rotatable electron-diffraction patterns, through which quasicrystals were discovered. In this project we will make use of these observables, by employing pump-probe ultrafast electron diffraction (UED) to study an archetypical icosahedral quasicrystal. By employing the ultrafast Debye-Waller effect and momentum-resolved ultrafast inelastic scattering (between Bragg spots), this will provide sensitivity to photoinduced phonon- and phason- dynamics, thus revealing the sub-picosecond evolution of their populations, and their interplay. Of particular interest is their evolution through short-lived “nonthermal” states, in which their populations disobey Bose-Einstein statistics.

• DFG Programme: Research Grants
• International Connection: Austria, Japan, Spain
• Cooperation Partners: Dr. Unai Atxitia Macizo; Professor Dr. Arthur Ernst; Professor Dr. Ryuji Tamura