Title: Disorder driven quantum phase transition

Speaker: Dr. Soumya Bera, Max Planck Institute, Dresden

Abstract : Disorder is ubiquitous and normally unavoidable in condensed matter samples and usually governs the low-temperature electronic properties of the material. For instance, in low dimensional disordered systems, the dynamics of electrons is determined by its wave nature. Due to quantum interference effects, instead of moving smoothly electrons can stay put at a single spot. First part of the talk will review the Anderson transition in disordered non-interacting system.

In the next part the talk will address, how the one-particle density matrix can be used to characterize the interaction-driven many- body localization transition in closed fermionic systems. The natural orbitals (the eigenstates of density matrix) are localized in the many-body localized phase and spread out when one enters the delocalized phase, while the occupation spectrum (the set of eigenvalues of density matrix) reveals the distinctive Fock-space structure of the many- body eigenstates, exhibiting a steplike discontinuity in the localized phase. The associated one-particle occupation entropy is small in the localized phase and large in the delocalized phase, with diverging fluctuations at the transition.