Seminars

Host: Melanie Müller Location: Building G

Non-equilibrium dynamics of laser-excited electrons in a metal

Femtosecond laser pulses irradiating a solid material induce a cascade of processes starting with the excitation of so-called hot electrons and passing through various relaxation processes. Several scattering mechanisms act on different timescales. At sufficiently high energy densities, phase transitions and ultrafast structural dynamics can be induced.We simulate the dynamics of a large ensemble of excited electrons using complete Boltzmann collision integrals. We consider the excitation of conduction electrons in a metal with visible light. On a femtosecond timescale, the electrons' energy distribution deviates strongly from a Fermi distribution. We extract spectral electron densities within specificenergy windows, and find complex behavior that cannot be matched with a single relaxation time.We show that electron-electron and electron-phonon scattering mutually influence each other during thermalization. For materials with several electronic systems, e.g. itinerant ferromagnets or dielectrics, we observe that temperatures and partial densities can be independent quantitieson picosecond timescales. [more]

High-power Ultrafast Moves into the Terahertz Domain

Terahertz Time Domain Spectroscopy (THz-TDS) has become a ubiquitous tool in many scientific fields and is also increasingly deployed in industrial settings. While these systems become more and more mature, efficient and lab-based THz generation methods combining broad bandwidth and high dynamic range (e.g., as provided by high THz average power and correspondingly high repetition rate) remain rare. [more]

Theory of Photo- and Electro-luminescence in Scanning Tunneling Microscopy

I will talk about the theoretical perspective on a microscopy technique that combines the atomic-scale resolution of a scanning-tunneling microscope (STM) with optics. [more]

Light-Matter Control of Quantum Materials

  • PC Department Seminar
  • Date: Aug 28, 2023
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Michael Sentef
  • University of Bremen & MPI for the Structure and Dynamics of Matter, Hamburg
  • Location: Building G
  • Room: 2.06
  • Host: Melanie Müller
Advances in time-resolved pump-probe spectroscopies have enabled us to follow the microscopic dynamics of quantum materials on femtosecond time scales. This gives us a glimpse into the inner workings of how complex, emergent functionalities of quantum many-body systems develop on ultrafast time scales or react to external forces. [more]

Ultrafast Exciton Dynamics in Moiré Heterostructures: a Time-resolved Momentum Microscopy Study

Transition metal dichalcogenides (TMDs) are an exciting model system to study ultrafast energy dissipation pathways, and to create and tailor emergent quantum phases [1,2]. The versatility of TMDs results from the confinement of optical excitations in two-dimensions and the concomitant strong Coulomb interaction that leads to excitonic quasiparticles with binding energies in the range of several 100 meV. [more]

Fully-atomistic Light-driven Dynamics in Plasmonic Cavities and Interfaces

The study of confined fields in plasmonic nanocavities and their interaction with molecules and nanostructures is an area of research with vast applications, including enhanced spectroscopy techniques as well as photoinduced/photocatalytic non-equilibrium phenomena. From the theoretical perspective, either classical electromagnetic models or atomistic/quantum descriptions are usually considered. However, in many cases these models ignore the electronic and nuclear quantum effects arising from the chemical nature and dynamics of a junction, such as tunneling, adsorption geometry, structure of the interface, vibrations, etc., or include them only approximately. Hence, a full quantum dynamical description is sometimes inescapable. [more]

Investigating Ultrafast Electron and Phonon Dynamics at the Atomic Scale

Electrons, phonons, and their mutual interactions are crucial for the complex phenomena in strongly correlated materials. In this talk, I will show that electron and phonon dynamics can be investigated at the atomic scale by combining THz pump-probe spectroscopy and a scanning tunneling microscope (STM) [1,2]. [more]
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