Seminar Notice

Speaker Prof. Soren Ulstrup (Aarhus University)
Date & Time 2017.12.11, 16:00~16:30
Place Bldg. 19, Rm. 210
Title Controlling the electronic structure of two-dimensional semiconductors in the real space and ultrafast time domains

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) 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. The latter
are exemplified by the presence of tunable band gaps and tightly bound excitons and trions. Here, I will discuss our recent efforts to synthesize single-layer TMDs such as MoS2 and WS2 using a variety of methods ranging from van der Waals epitaxy [1] to manual exfoliation, transfer and assembly of TMD-based heterostructures with other 2D materials [2,3]. Characterization of the electronic properties of such materials is carried out using a combination of angle-resolved photoemission (ARPES) experiments that incorporate either
ultrafast time-resolution (TR-ARPES) or micro- to nano-scale spatial resolution (microARPES/nanoARPES). I will show how ultrafast band gap tuning and control of the spin- and valley-degrees of freedom in TMDs can be achieved and observed in pump-probe experiments [4]. Finally, I will address how the substrate material influences the band structure and many-body interactions in 2D heterostructures based on spatially-resolved photoemission experiments [2,3].

[1] J. A. Miwa, M. Dendzik et al.: Van der Waals Epitaxy of Two-Dimensional MoS2-Graphene
Heterostructures in Ultrahigh Vacuum. ACS Nano 9, 6502 (2015)
[2] S. Ulstrup, J. Katoch et al.: Spatially Resolved Electronic Properties of Single-Layer WS2 on
Transition Metal Oxides. ACS Nano 10, 10058 (2016).
[3] J. Katoch, S. Ulstrup et al.: Giant spin-splitting and gap renormalization driven by trions in
single-layer WS2/hBN heterostructures. arXiv:1705.04866 (2017).
[4] S. Ulstrup, A. G. Cabo et al.: Spin and Valley Control of Free Carriers in Single-Layer WS2.
Physical Review B: Rapid Communications 95, 041405(R) (2017).


Host: Prof. Changyoung Kim