Matrix Product State Approaches to Non-equilibrium Spectral Quantities of Strongly Correlated Fermions in One Dimension
von Constantin Meyer
Datum der mündl. Prüfung:2022-04-19
Betreuer:PD Dr. Salvatore R. Manmana
Gutachter:PD Dr. Salvatore R. Manmana
Gutachter:Prof. Dr. Stefan Kehrein
EnglischIn this thesis we numerically study non-equilibrium phenomena in one-dimensional quantum many-body systems. We discuss extensions of the concepts of spectral functions and of the optical conductivity to time-dependent non-equilibrium setups and compute these quantities by means of matrix product state (MPS)-based methods. In a first application we study the effect of a spin-selective particle-hole-like excitation on a Hubbard model with an additional magnetic superstructure. Following the excitation, this model exhibits a stable charge density, as well as a stable spin density pattern mirroring the superstructure. For interacting systems we find an additional in-gap signal in the spectral function in the spin direction opposite to the one we applied the excitation in, which also persists over time. Our results are confirmed by a computation of the corresponding optical conductivity. We interpret our results as a trace of an exciton, which we support by an analysis in the atomic limit, and therefore refer to our findings as a peculiar spinful exciton. In contrast to many other setups, no long-range Coulomb term is needed for this exciton to form. Second, we apply the same calculus to compute non-equilibrium spectral functions of a Floquet-driven system of interacting spinless fermions in the charge density wave (CDW) Mott insulator phase, where we model the driving through a Peierls substitution ansatz. We find good agreement of our results with computations from an effective model obtained from Floquet theory, as well as Floquet side bands. These, however, do not show at all times as expected. Furthermore, another in-gap signal occurs, that is somewhat reminiscent of free particles, which goes hand in hand with a melting of the CDW pattern.
Keywords: matrix product states; non-equilibrium; out-of-equilibrium; photo excitation; ARPES; MPS; DMRG; optical conductivity; spectral function; Floquet systems; driven systems