| Time：1130327 (Wed.) 14:20~16:20 Speaker：Prof.柳澤達也(Tatsuya YANAGISAWA) 北海道大學物理學系/Department of Physics, Hokkaido University, Japan Title：Observation of Multipoles in the Solid State using Ultrasound Abstract：Ultrasonic measurement is one of the unique and powerful techniques to probe anisotropic local charge distributions and fluctuations in solids [1] associated with the electric/magnetic-multipolar moments of d- or f-orbital, valence/charge fluctuations, atomic vacancy in Si and diamond, and atomic oscillation so called ‘rattling’. These are difficult to be detected by a typical technique such as electrical resistivity and magnetization. In general, the principle of the ultrasonic measurement in solids is based on motoring local strains of the lattice induced by a propagating elastic wave, which is coupled to the local charge distribution and interaction between charge and lattice vibration. As a result, the longitudinal and transverse acoustic waves can observe the multipolar responses of different symmetries “spectroscopically” (Fig. 1). Since the above-mentioned electric degrees of freedom cause a spontaneous symmetry breaking and induce lattice instabilities in some compounds of the strongly correlated electron systems, therefore, it is very important to get the information regarding physical acoustics when exploring a new material. I would like to briefly introduce the recent progress of the ultrasonic studies on strongly correlated electron systems [2-4], and the story of our discovery of elastic softening in the synthetic diamond [5]. [1] B. Lüthi, Physical Acoustics in the Solid State (Springer, Berlin, 2006). [2] T. Yanagisawa et al., Phys. Rev. Lett. 123, 067201 (2019). [3] T. Yanagisawa et al., Phys. Rev. Lett. 126, 157201 (2021). [4] R. Hibino et al., J. Phys. Soc. Jpn. 92, 074708 (2023). [5] T. Yanagisawa et al., arXiv:2401.03377. Place：B101, Gongguan Campus, NTNU https://www2.phy.ntnu.edu.tw/wp-content/uploads/2024/01/1130327_Abstract-1.pdf |