Thema der Dissertation:
Electron dynamics in quasi-2D Van der Waals crystals studied by time- and angle-resolved photoemission spectroscopy
Electron dynamics in quasi-2D Van der Waals crystals studied by time- and angle-resolved photoemission spectroscopy
Abstract: This thesis explores the ultrafast electron dynamics in quasi-two-dimensional (2D) layered Van der Waals bulk crystals via time-and angle-resolved photoemission spectroscopy. It provides a fundamental perspective on the spin- and lattice dependent non-equilibrium transient electronic structure of two materials classes: 3D topological insulators (TIs) and charge-density wave (CDW) materials, both being considered for the use in opto-electronic applications. TIs as, e.g., Sb2Te3 present model systems for studying photo-excited spin-polarized currents on their topologically protected surface states, whereas the CDW system 1T-TiSe2 is discussed to exhibit a novel excitonic insulator phase that competes with a simultaneously launched CDW.
In my defense talk, I will discuss fluence-dependent electron and lattice dynamics in the correlated CDW material 1T-TiSe2 for its normal and distorted phase. Optical driving of its phase transition reveals distinctly different responses depending on the excitation fluence. I will present evidence on the periodic modulation of the CDW gap in 1T-TiSe2 by monitoring coherent oscillations of its occupied and unoccupied electronic structure. Depending on the doping with photo-carriers, I will show anti-phase modulations of the occupied Se 4p valence bands and back-folded conduction band near Brillouin zone center with either the CDW amplitude mode or close to its second harmonic. This observation is attributed to a progressive modification of the potential energy landscape from a double to a single well potential due to an increased screening and a concomitant transition from an impulsive to a displacive excitation of the CDW mode.
In my defense talk, I will discuss fluence-dependent electron and lattice dynamics in the correlated CDW material 1T-TiSe2 for its normal and distorted phase. Optical driving of its phase transition reveals distinctly different responses depending on the excitation fluence. I will present evidence on the periodic modulation of the CDW gap in 1T-TiSe2 by monitoring coherent oscillations of its occupied and unoccupied electronic structure. Depending on the doping with photo-carriers, I will show anti-phase modulations of the occupied Se 4p valence bands and back-folded conduction band near Brillouin zone center with either the CDW amplitude mode or close to its second harmonic. This observation is attributed to a progressive modification of the potential energy landscape from a double to a single well potential due to an increased screening and a concomitant transition from an impulsive to a displacive excitation of the CDW mode.
Zeit & Ort
01.07.2026 | 11:00
Hörsaal A (1.3.14)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)