Electronic and Structural Dynamics in Solids: A Momentum-Resolved View on Microscopic Coupling and Correlation Phenomena
Dr. Ralph Ernstorfer
Department of Physical Chemistry - Fritz Haber Institute of the Max Planck Society - Berlin
17:00 - 18:00 Tuesday 21 June 2016 KFU HS 5.01 The coupling and mutual dependence of electronic and vibrational degrees of freedom is at the heart of microscopic as well as macroscopic phenomena in condensed matter. Ultrafast pump-probe techniques provide experimental access to these coupling and correlation effects by revealing the microscopic
response to specific excitation of a material. In particular, we employ time- and angle-resolved photoelectron spectroscopy (trARPES) and femtosecond electron diffraction (FED) [1] and imaging [2] in
order to obtain a momentum-resolved view on the dynamics of electrons and phonons.
I will discuss electron-lattice interaction and electron dynamics in two classes of materials. First, the electron-phonon coupling in the free-electron metal aluminium is revisited and quantitatively investigated with FED and first-principle calculations. Our results challenge the validity of the twotemperature
approximation and we propose a refined non-thermal lattice model [3].
Second, I will discuss ultrafast electron and phonon dynamics in the semiconducting transition metal dichalcogenide WSe2. TrARPES with fs XUV pulses reveals the evolution of spin- and pseudospin-polarized excited states and allows for mapping of the conduction band structure in the entire Brillouin zone. The complementary momentum-resolved dynamics of phonons in this material is studied by FED.
[1] L. Waldecker et al., J. Appl. Phys. 117, 044903 (2015).
[2] M. Müller et al., Nature Communications 5, 5292 (2014).
M. Müller et al., ACS Photonics 3, 611 (2016).
[3] L. Waldecker et al., Phys. Rev. X 6, 021003 (2016).
[4] R. Bertoni et al., arXiv:1606.03218
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