Микроволновый семинар. Белтуков

Yaroslav Beltukov (Ioffe Institute)

'Vibrational properties of amorphous solids'

Abstract: The propagation of vibrational excitations in disordered systems is one of the advanced problems in condensed matter physics. In particular, this phenomenon is responsible for the thermal conductivity of amorphous dielectrics (glasses). However, the microscopic mechanism of the heat transfer above 20 K is still poorly understood. Recent numerical simulations of amorphous silicon and silica show that vibrational modes in the corresponding frequency range (called “diffusons”) are delocalized, however they are completely different from low-frequency acoustic phonons. We present a stable random matrix model of an amorphous solid. In this model one can vary the strength of disorder going from a perfect crystal to extremely disordered soft medium without macroscopic rigidity. We show that real amorphous solids are close to the second limiting case, and that diffusons occupy the dominant part of the vibrational spectrum. The crossover frequency between acoustic phonons and diffusons is determined by the Ioffe-Regel criterion. We show that this crossover is also responsible for the boson peak in glasses.