др Вељко Јанковић

15. априла 2024.

У оквиру семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 18. априла 2024. године у 14 часова у читаоници библиотеке „др Драган Поповић“, др Вељко Јанковић (Институт за физику у Београду) одржаће предавање:

Taking the road less traveled towards dynamical properties of interacting electron–phonon systems


The transport of electrons limited by scattering on quantum lattice vibrations is usually depicted as a series of spatially and temporally well-separated scattering events undergone by the appropriately renormalized electron. This simplified picture is inappropriate whenever consecutive collisions overlap in space and time, which is typical for systems characterized by the convergence of relevant energy scales (e.g., narrow-band semiconductors or photosynthetic molecular aggregates). Within the simplest model of such systems, the multimode Holstein model, the need for genuine nonperturbative results on electronic dynamics has been fulfilled by approaches originating from the theory of open quantum systems, such as the hierarchical equations of motion (HEOM) [1]. Within the single-mode Holstein model, widely studied in condensed-matter physics, the HEOM method confronts serious numerical challenges [2], whose overcoming is an active research avenue [2,3].

In this talk, we will present our momentum-space implementation of HEOM equations for real-time finite-temperature correlation functions of the single-mode Holstein model [4,5]. We will describe our hierarchy closing strategy to overcome numerical instabilities. Using this strategy, we can capture the long-time electron’s diffusive motion and obtain reliable results for the electron mobility and optical conductivity in a wide range of model parameters. We find deviations from the simplified transport picture already in the intermediate-interaction regime, where, in addition to the Drude-like peak, we observe a finite-frequency peak in the optical response. The latter is tightly connected to a time-limited slow-down of the electron on intermediate time scales between ballistic and diffusive dynamics.

[1] Y. Tanimura, J. Chem. Phys. 153, 020901 (2020).
[2] I. S. Dunn et al., J. Chem. Phys. 150, 184109 (2019).
[3] Y. Yan et al., J. Chem. Phys. 153, 204109 (2020).
[4] V. Janković and N. Vukmirović, Phys. Rev. B 105, 054311 (2022).
[5] V. Janković, J. Chem. Phys. 159, 094113 (2023).