8:00 PM - FF01.16.24
Multiexciton and Excited States of Excitons in Monolayer MoS2 Observed Using Photoluminescence Spectroscopy
Juhi Pandey1,Ajay Soni1
Indian Institute of Technology Mandi1
Two-dimensional semiconducting transition metal dichalcogenides (TMDCs) provides rich platform to study several interesting many body complexes such as excitons, trions, biexcitons and excitonic states for fundamental understanding and optoelectronic applications.1, 2 Remarkably, strong Coulombic interaction with reduced dielectric screening effect in TMDCs makes experimental realization of such complexes even at room temperature which are otherwise observed at low temperatures. Further, similar to Hydrogen atoms, excitons exhibit excited states known as Rydberg states which are under scientific exploration and opens up new avenues for future quantum information processing, optoelectronic and photonics.3 Owing to weak signal from biexciton and excitonic Rydberg states in TMDCs, such complexes are less understood than excitons and trion. Further, the extent of spin orbit splitting of valence band due to d-orbital of transition metal plays an important role in observation of excitonic states. Large spin orbit splitting (> 400 meV) resulted in observation of series of Rydberg states of A exciton in ML of WS2 and WSe2 using several linear and non-linear spectroscopic techniques. On the contrary, the small spin orbit splitting ~ 150 meV in ML MoS2 provides an additional challenge in distinct realization of 2s state of A exciton (A2s) because of the overlap with large spectral width of B exciton. Recently, A2s state in ML MoS2 has been theoretically predicted and experimentally observed in ML MoS2 encapsulated by hBN ~ 2.1 eV using advance non-linear spectroscopic measurements.5 In our study, we performed temperature dependent photoluminescence (PL) studies up to 4 K to minimize spectral width of A and B excitons and accessed excitonic complexes as well Rydberg states. We discuss about the systematic observation of biexciton (~ 1.90 eV), sulfur vacancy mediated bound exciton (1.85 eV) and A2s state (~ 2.13 eV) distinct from A- trion (~ 1.92 eV), A exciton (~ 1.96 eV) and B exciton (~ 2.07 eV) in ML MoS2 using laser power dependent and temperature dependent PL spectroscopy from 4 K to 300 K. At low temperatures, the observed weak signal of excited state A2s ultimately merges with spectral broadening of B exciton with raising temperatures.6 From the estimated binding energy of biexciton (~ 60 meV), we suggest that biexcitons can be stable even at room temperature.
1. Lee, H. S.; Kim, M. S.; Kim, H.; Lee, Y. H. Physical Review B 2016, 93, (14), 140409.
2. Mak, K. F.; He, K.; Shan, J.; Heinz, T. F. Nature Nanotechnology 2012, 7, 494.
3. Chernikov, A.; Berkelbach, T. C.; Hill, H. M.; Rigosi, A.; Li, Y.; Aslan, O. B.; Reichman, D. R.; Hybertsen, M. S.; Heinz, T. F. Physical Review Letters 2014, 113, (7), 076802.
4. Liu, E.; van Baren, J.; Taniguchi, T.; Watanabe, K.; Chang, Y.-C.; Lui, C. H. Physical Review B 2019, 99, (20), 205420.
5. Robert, C.; Semina, M. A.; Cadiz, F.; Manca, M.; Courtade, E.; Taniguchi, T.; Watanabe, K.; Cai, H.; Tongay, S.; Lassagne, B.; Renucci, P.; Amand, T.; Marie, X.; Glazov, M. M.; Urbaszek, B. Physical Review Materials 2018, 2, (1), 011001.
6. Pandey, J.; Soni, A. Applied Surface Science 2019, 463, 52-57.