Field theoretical extensions of many-body theories

S. Fritzsche

D. ter Haar

Matteo Ballerini Puviani, F. Manghi

In this paper we present a general theoretical framework to study interacting electrons under the influence of an external time-periodic driving, such as a homogeneous laser field. This is performed through a true many-body calculation and the use of Floquet theory. In particular, we consider a linear atomic chain using the Hubbard model to describe the short-ranged Coulomb interactions between electrons, plus Cluster Perturbation Theory to embed the many-body exact solution for a finite system into both an extended and an infinite lattice. Due to the presence of the external time-periodic perturbation, the electronic problem can be mapped into the study of photon-dressed quasiparticles thanks to Floquet theorem, keeping into account of all the virtual processes (absorption and emission of photons by electrons) with the laser field. This leads to an extension of the many-body static theories to out-of-equilibrium systems. This theoretical approach allowed us to show how the electronic properties of the system can be controlled and tuned varying the laser parameters. Above all, an inverse insulator-to-metal transition can be obtained for the one dimensional infinite lattice, and edge localized states appear as a finite size effect in an extended truncated chain.

Alexander I. Lichtenstein

In this lecture we give an introduction to theoretical description of strongly correlated materials based on dynamical mean-¿eld theory (DMFT) and its extensions.The goal of this theoretical construction is to retain the many-body aspects of local atomic physics within the extended solid.The effects of short-range non-local correlations within cluster extensions of the DMFT scheme, as well as long-range Àuctuations within the fully renormalized dual-fermion perturbation scheme are discussed extensively.Recent progress in the numerical solution of the DMFT effective quantum impurity problem within the recently developed continuous-time Quantum Monte Carlo schemes is reviewed.We then describe realistic extensions of this approach which combine the accuracy of ¿rst-principle Density-Functional Theory with the treatment of local many-body effects within DMFT.

J W Clark, MANUEL DE LLANO, Mauricio Fortes +1 more

Eugene Paul Wigner

Physicists very rarely boast about the immense extension of the area of physics which took place in the very short period of about 300 years since the birth of "our" discipline. The macroscopic bodies similarly obey laws, those of classical physics, with a similar accuracy. The German physicist D. Zeh has called attention to the fact that the quantum theoretical energy levels of a reasonably macroscopic body are so close to each other that even a single atom or electron, though spatially well separated from it, will influence it in the quantum theoretical sense. The general theory of relativity is a macroscopic theory. In the case just considered it implies the behavior of many living beings; in the case, it implies the consideration of such properties of a single macroscopic object which are macroscopically definable and observable.