Topic: Charge diffusion in metallic alloys: beyond coherent potential approximationSpeaker: Professor Václav Janiš, Institute of Physics, Czech Academy of Sciences (AVCR)
Date and time: May 23, 14:00–15:00Venue: Room 103, #5 Building of SPSTElectronic properties of metallic alloys are widely described with sufficient reliability within the local coherent potential approximation (CPA). When the chemical disorder is weak, it is also well suited for transport properties. Backscattering, missed in the CPA, dominates and leads to Anderson localization in the opposite limit of strong disorder. Completely different approaches based on the renormalization group are used to describe this phenomenon. There is presently no consistent perturbative scheme extending the CPA that would lead to Anderson localization. The problem with the extensions of the CPA is the inability to keep the diagrammatic perturbation expansion conserving beyond single-site scattering.We briefly summarize the fundamental properties of the CPA for a Fermi gas in a random lattice potential and introduce Ward identities guaranteeing macroscopic conservation laws. Next, we introduce parquet equations for the two-particle irreducible vertices that lead to the necessary two-particle self-consistency. Even if we match the two-particle irreducible vertex of the parquet equations with the self-energy appropriately, macroscopic conservation laws are generally broken. To amend this, we introduce a correcting term at the two-particle level so that the response functions comply with the demanded conservation laws. A systematic perturbation expansion with two-particle self-consistency is obtained beyond the local mean field.Biography:
Prof. Václav Janiš, a distinguished condensed matter theorist and senior researcher at the Institute of Physics of the Czech Academy of Sciences, has significantly contributed to the field of non-relativistic quantum many-body theory. His extensive experience focusing on non-perturbative methods, many-body Green functions, and collective and critical phenomena of strongly correlated electrons has pushed the boundaries of knowledge. His research interests include quantum dynamics in Fermi systems with broken symmetry and long-range order, superconductivity, itinerant magnetism, charge diffusion, spin glasses, and quantum critical behavior. His research results are at the forefront of theoretical investigations in the physics of correlated electrons.
