Ultrafast THz- and Infrared-Spectroscopy of Strongly Bound Excitons in GaN, ZnO and Transition-Metal-Dichalcogenides
Final Report Abstract
We performed a variety of ultrafast spectroscopic methods and experiments to study charge carrier dynamics in two-dimensional semiconductors. The typical schema for such an experiments is to drive an electronic system out of its equilibrium state using an extreme intense light pulse (pump) with a temporal resolution of sub 100 fs (fs millionth of a billionth of a second – 1e-15 s). A second light pulse (probe) at a different energy and typically lower intensity allows to subsequently monitor the state of the system after the excitation process. Performing the same measurements for different delays can reveal the charge carrier dynamics and allows for insights into the microscopic driving mechanism behind the scene. Here, we used optical pump and Terahertz probe or extreme ultraviolet probe spectroscopy to study the charge carrier dynamics in the transition-metal dichalcogenide MoSe2 and other two-dimensional systems. These material systems may play an important role in future electronic devices and are candidates to replace Silicon as the main component of our electronics. Furthermore, they are showing a plethora of interesting intrinsic quantum mechanical properties. We are highly interested to understand those phenomena of multi-particle dynamics and interactions which may allow us to use quantum mechanical effects in the design of future electronics. Our main results was the observation a “so-called” excitonic state directly visualized in momentum space of the transition metal dichalcogenide. Excitons are two-particle states formed from an electron and a hole (missing electronic state in the remaining “sea” of electrons after optical excitation of the solid state sample and is already subject of physical studies for decades. For the best of our knowledge we believe we observed a band-gap exciton dissociation process in angle-resolved photoemission spectroscopy for the first time.
Publications
- Broadband Transient THz Conductivity of the Transition-Metal Dichalcogenide MoS2, Proc. of SPIE Vol. 9361, 93611J-1 (2015)
J. H. Buß, R. P. Smith, G. Coslovich, and R. A. Kaindl
(See online at https://dx.doi.org/10.1117/12.2080748) - Ultrafast extreme-ultraviolet ARPES studies of electronic dynamics in two-dimensional materials, Proc. of SPIE 10102, 1010201 (2017)
J. H. Buß, J. Maklar, F. Joucken, H. Wang, Y. Xu, S.-K. Mo, A. Lanzara, and R. A. Kaindl
(See online at https://dx.doi.org/10.1117/12.2251249)
