Tunable Exciton-trion State in Twisted Bilayer WSe2 | Pramoda Kumar Nayak

Summary :
⁣Twist angle between the adjacent layers of Transition Metal Dichalcogenides (TMDCs) provides an exotic degrees of freedom to tune the various optical and electrical properties in the field of twistronics. To realize the practical applications of twistronics, it is importance to tune the interlayer twist angle on large scales as the varying twist angle results in strong tuning of the indirect optical transition energy and Raman modes. In this work, we demonstrate the tunable Photoluminescence (PL) properties and the Raman modes of bilayer WSe2 through interlayer twist with a wide angle variation. PL and Raman spectra show that the interlayer coupling is highly sensitive to twist angle. Here, the stacking of CVD grown WSe2 bilayers was varied from 00 to 600 angle, which leads the homo-bilayer from AA to AB stacking orientation with a 60° periodic change of their PL spectra. We observed that, the twist angle can continuously change the indirect band-gap trion state at Q-K point in WSe2 homo-structures. At room temperature, the exciton and trion states are present at 00 twist angle and with increase in the twist angle, the indirect trion state dominates over the excitonic state. This PL modulation is attributed to the change of the interlayer coupling between the adjacent WSe2 layers. A systematic variation of Raman modes also revealed the manipulation of phonons with the twist angle in WSe2. These results enrich the understanding of the PL emission and interlayer coupling, which is significant in the field of twistronics.


About Author :
⁣Dr. Pramoda Kumar Nayak is working as adjunct Professor at Dept. of Physics, IIT Madras since 2017. His research interest is to explore intriguing properties of two dimensional (2D) materials including Graphene, transition metal dichaclogenides, topological insulators and their heterostructures. He has published more than 50 international journals including (Nature, Nano Letters, ACS Nano, APL and so on), 6 book chapters, 04 edited books and one book so far in his research carrier. He has received several awards and recognitions, which includes BK21Plus Research Fellowship, South Korea (2015), 2 prestigious Ramanujan Fellowship from Department of Science and Technology, India (2017), Younger Achiever Award from Institute of Scholars (InSc), 2020 and Best scientist Award from EET CRS in 5th academic Brand award 2020.