Wydarzenia

Seminarium w Instytucie Niskich Temperatur i Badań Strukturalnych PAN

Physics of disorder in particle mixtures

prof. dr Klaus Ziegler

University of Augsburg, Niemcy

A mixture of two types of particles (e.g. two types of atomic species in an ultracold gas or a mixture of fermions and phonons in a crystalline solid) can generate interesting physical properties due to competing length scales. One possible mechanism is phase separation, the other one is Anderson localization. If one particle species is heavier than the other, we can neglect its quantum fluctuations and obtain a quantum theory of the light species in the presence of quenched fluctuations due to the heavier species. This problem is mapped either onto a Falicov-Kimball model with a discrete spin or a model with a continuous spin degree of freedom. The distribution of the spins is determined by the dynamics of light atoms. This strongly interacting system has two different quantum phases, where one phase is characterized by a gap opening in the spectrum of the light atoms. The transition between these phases is either driven by the interaction strength or by thermal fluctuations. Moreover, there is an Anderson transition, where the light particles are localized for temperatures above a critical temperature T_c. We study the quantum states analytically in terms of the underlying dynamical symmetry structure and numerically for an expanding cloud of particles, using a single-parameter scaling approach for the localization length.