Seminar Announcement: Tatsuya Mori
Data pubblicazione: 24-mar-2019 19.20.07
Thursday, 21 March 2019, 15:00
Sala Grande Palazzina B via alla Cascata 56/C
"Boson peak and fracton in glass and single crystal probed by terahertz spectroscopy"
Division of Materials Science Faculty of Pure and Applied Sciences,
University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8573,
In disordered materials, the boson peak (BP) is observed in the terahertz region as a universal feature of atomic vibration . The BP closely relates to the universal temperature behavior of thermal properties of glassy system which is one of the unsolved problems in glass physics. Meanwhile, for polymer glass, the so-called fracton  excitation will universally appear in the frequency range above the BP frequency, and it will be originated from the self-similar connectivity of structural units. Interestingly, some particular single crystals such as some thermoelectric materials [3,5] and pure relaxor materials , show the universal temperature dependence of thermal properties of glassy system. Those anomalous thermal properties are originated from the off-center rattling phonon modes which correspond to the BP of actual glassy materials . In addition, the fracton in single crystal is observed in the pure relaxors [4,7], by the connection of the dipole-dipole moments having a fractal structure. In the presentation, we show how to detect these universal excitations by terahertz spectroscopy  and discuss the difference of behaviors of BP and fracton between actual glass materials and single crystals.