Two-dimensional (2D) materials exhibit a diverse collection of intriguing electronic phenomena. These include single-particle effects related to new spin and valley physics, as well as exotic many-body interactions that may profoundly influence charge carrier dynamics in these materials. Here, I will discuss time- and angle-resolved hotoemission (TR-ARPES) experiments on single- and bi-layer transition metal dichalcogenides (TMDs), which have been synthesized using van der Waals epitaxy [1]. Such TR-ARPES experiments have previously provided detailed information on hot electron relaxation dynamics in graphene due to directly revealing the time-dependent changes in the material’s band structure and separating electron-phonon interactions in the time domain [2]. I will show how ultrafast band gap tuning [3] and control of the spin- and valley-degrees of freedom can be achieved and observed in pump-probe experiments on semiconducting single-layer TMDs such as MoS 2 and WS 2 [4]. The polarization dependence of excited carriers in bi-layer MoS 2 will be discussed. Recent results on the metallic TMD TaS 2 will also be presented, and I will discuss the observation and analysis of time dependent electron-electron interactions leading to strong band renormalization effects around the Fermi level of 2D TaS 2 . [1] J. A. Miwa, M. Dendzik et al.: Van der Waals Epitaxy of Two-Dimensional MoS 2 -Graphene Heterostructures in Ultrahigh Vacuum. ACS Nano 9, 6502 (2015) [2] J. C. Johannsen, S. Ulstrup et al.: Direct View of Hot Carrier Dynamics in Graphene. Phys. Rev. Lett. 111, 027403 (2013). [3] S. Ulstrup, A. G. Cabo et al.: Ultrafast Band Structure Control of a Two-Dimensional Heterostructure. ACS Nano 10, 6315 (2016). [4] S. Ulstrup, A. G. Cabo et al.: Spin and Valley Control of Free Carriers in Single-Layer WS 2. Physical Review B: Rapid Communications 95, 041405(R) (2017).
We would like to invite you to suggest speakers from local groups or visitors for any slot that is not filled yet. Looking forward to seeing you there!
Kind regards,
Iman (iman.mahyaeh@fysik.su.se
Yaron (yaron.kedem@fysik.su.se)
Flore (flore.kunst@fysik.su.se)
Yago (yagoferreiros@gmail.com)
Matthias (matthias.geilhufe@su.se)