Electronic devices : Can be scaled and integrated but limited in signal processing speed

Photonic devices : Fast signal processing speed but large device dimensions

Excitonic devices : Combine best of the two – fast, energy efficient and can be integrated



Two-dimensional transition metal dichalcogenides (TMDs) exhibit excitons, optically excited coulomb bound electron-hole pair, stable even at room temperature and are potential candidates for emerging excitonic devices. Several excitonic states with distinct properties can coexist in these materials. Depending on the application, some of these excitonic states maybe more suitable than others and hence need to be selectively enhanced or supressed.



In the 1st seminar, experimental observations of momentum direct and indirect excitonic states in monolayer [1] and multilayer [2, 3] TMDs were discussed. It was shown that incorporation of gold nanoparticles in these systems can selectively enhance or supress specific excitonic states due to plasmon induced effects.



In this talk, the space indirect or interlayer (IL) excitonic states in bilayer (BL) TMD systems will be discussed. Herein, two different BL systems will be presented, where different excitonic states emerged in BL which were absent in the constituent monolayers.

a) WSe2 homo-bilayer: The relative stacking angle between the two layers selectively enhanced or supressed different excitonic states, as observed from experiments [4].

b) MoSe2/MoS2 hetero-bilayer: A small lattice mismatch of ~ 4% resulted in a long range periodic potential of period ~ 7 nm. This spatially varying potential along with type-2 band alignment resulted in band hybridization and different IL excitons [5].

These results can be used to selectively enhance or supress specific excitonic states and may help in engineering excitonic devices for optoelectronic applications.



Finally, some interesting properties of Muscovite mica (MuM) flakes will be presented. It was observed that the in-plane dc electrical conductivity of few-layer MuM flakes was found to be thickness dependent and was three orders of magnitude larger in 10 nm thick flake compared to that in 20 nm thick flake.



[1] A. Arora, et al., Appl. Phys. Lett., 114(20), 201101 (2019).

[2] T. Dixit, A. Arora, et al., ACS Omega, 3(10), 14097-14102 (2018).

[3] T. Dixit, A. Arora, et al., IEEE Photonics Journal, 11(5), 4501106 (2019).

[4] A. Arora, et al., Nanophotonics, 9(12), 3881-3887 (2020).

[5] A. Arora, et al., Phys. Rev. B, 103(20), 205400 (2021).