Antonija Grubisic Cabo (1), Soren Ulstrup (2), Jill A. Miwa (1), Jonathon M. Riley (3), Signe S. Gronborg (1), Jens C. Johannsen (4), Cephise Cacho (5), Oliver Alexander (5), Richard T. Chapman (5), Emma Springate (5), Marco Bianchi (1), Maciej Dendzik (1), Jeppe V. Lauritsen(1), Phil D. C. King (3) and Philip Hofmann (1) 1. Aarhus University, Denmark, 2. Berkeley National Laboratory, USA, 3. St. Andrews University, UK,4. EPFL, Switzerland, 5. Rutherford Appleton Laboratory, UK  Time- and angle-resolved- photoemission spectroscopy has been used to directly measure the excited carriers dynamics in epitaxial single layer MoS2 grown on either Au(111) or on graphene. For MoS2/Au(111) we determine an ultrafast (50 fs) extraction of excited free carriers via the metal and ascertain a direct quasiparticle band gap of 1.95 eV, which is significantly smaller than the theoretically estimated value for free-standing MoS2. This can be explained by a strong renormalisation of the band gap [1]. For the model 2D heterostructure of MoS2 on graphene, we are able to determine the layer-resolved band structure and separate the excited carrier dynamicsof MoS2 and graphene. On top of a static band gap reduction in MoS2 due to the screening of the nearby graphene, our results reveal a pronounced dynamic renormalisation of the quasiparticle band gap, reducing it by up to approximately 400 meV on femtosecond timescales following optical excitation. This results from a persistence of strong electronic interactions despite the environmental screening by the doped graphene [2]. These results show a large degree of tuneability of the electronic structure and electron dynamics within the van der Waals heterostructure. [1] A. Grubisic Cabo, J. A. Miwa et al., Nano Letters 15, 5883-5887 (2015) [2] S. Ulstrup, A. Grubisic Cabo et al., submitted to ACS Nano (2016)  Antonija Grubisic Cabo is a PhD student at the Interdisciplinary Nanoscience Center (iNANO) at Aarhus University. Her main research focus is on the possibility of using graphene in industrial applications and on the electronic structure and excited electron dynamics of novel 2D materials such as transition metal dichalcogenides. Antonija has experience in various UHV techniques, with special dedication to synchrotron- and laser-based techniques such as Angle Resolved Photoemission Spectroscopy (ARPES) and Time-Resolved ARPES (TR-ARPES). Prior to her PhD, she has received her M.S. in Physics in 2014 from the University of Zagreb, Croatia, where she worked mainly with complex magnetic systems. |