[institut] [phys4phys] SCL Seminar (in person): Janez Bonča, Monday, 27 June, 14:00

[Darko Tanaskovic]

Dear colleagues,

You are cordially invited to the SCL seminar of the Center for the Study 
of Complex Systems, which will be held on Monday, June 27 at 14:00 in 
the library reading room “Dr. Dragan Popović" of the Institute of 
Physics Belgrade. The talk entitled

"Dynamical properties  of a polaron coupled to dispersive optical 
phonons"

will be given by Janez Bonča (Faculty of Mathematics and Physics, 
University of Ljubljana; "Jožef Stefan" Institute, Ljubljana)

Abstract of the talk:

In the first part we will present the  study of static and dynamic 
properties of an electron coupled to dispersive quantum optical phonons 
in the framework of the Holstein model defined on a one–dimensional 
lattice [1]. Calculations are performed using the Lanczos algorithm 
based on a highly efficient construction of the variational Hilbert 
space. Even small phonon dispersion has a profound effect on the low 
energy optical response. While the upward phonon dispersion broadens the 
optical spectra due to single phonon excitations, the downward 
dispersion has the opposite effect. With increasing dispersion a 
multi–phonon excitation (MPE) state becomes the lowest excited state of 
the system at zero momentum and determines the low–frequency response of 
the optical conductivity where the threshold for optical absorption 
moves below the single–phonon frequency. Low–energy MPEs should be 
observable in systems with strong optical phonon dispersion in optical 
as well as angle resolved photoemission experiments.

In the second part we will discuss  Holstein polaron spectral function 
using the finite–temperature (T) Lanczos method [2]. With increasing T 
additional features in the  spectral function emerge even at 
temperatures below the phonon frequency. We observe a substantial spread 
of the spectral weight towards lower frequencies and the broadening of 
the quasiparticle (QP) peak. In the weak coupling regime the QP peak 
merges with the continuum in the high-T limit. In the strong coupling 
regime the main features of the low–T spectral function remain 
detectable up to the highest T used in our calculations. We will also 
present results of the electron removal spectral function as relevant 
for angle resolved photo emission experiments.

If time permits,  we will also discuss some relaxation properties of the 
electron coupled to various bosonic excitations [3].

References:
[1] J. Bonča, S. A. Trugman, Phys. Rev. B 103, 054304 (2021)
[2] J. Bonča, S. A. Trugman, and M. Berçiu, Phys. Rev. B 100, 094307 
(2019).
[3] J. Kogoj, M. Mierzejewski and J. Bonča, Phys. Rev. Lett., 117, 
227002 (2016).


Best regards,
Darko Tanaskovic