Electron-hole plasma formation dynamics observed through exciton-plasma interactions in transition metal dichalcogenides

2021 ◽  
Vol 104 (7) ◽  
Author(s):  
Manobina Karmakar ◽  
Subhrajit Mukherjee ◽  
Samit K. Ray ◽  
Prasanta Kumar Datta
2020 ◽  
Vol 10 ◽  
pp. 184798042095509
Author(s):  
Ankit Kumar Verma ◽  
Federico Raffone ◽  
Giancarlo Cicero

Two-dimensional transition metal dichalcogenides have gained great attention because of their peculiar physical properties that make them interesting for a wide range of applications. Lately, alloying between different transition metal dichalcogenides has been proposed as an approach to control two-dimensional phase stability and to obtain compounds with tailored characteristics. In this theoretical study, we predict the phase diagram and the electronic properties of Mo xTi1− xS2 at varying stoichiometry and show how the material is metallic, when titanium is the predominant species, while it behaves as a p-doped semiconductor, when approaching pure MoS2 composition. Correspondingly, the thermodynamically most stable phase switches from the tetragonal to the hexagonal one. Further, we present an example which shows how the proposed alloys can be used to obtain new vertical two-dimensional heterostructures achieving effective electron/hole separation.


2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Chiara Trovatello ◽  
Florian Katsch ◽  
Nicholas J. Borys ◽  
Malte Selig ◽  
Kaiyuan Yao ◽  
...  

Abstract The equilibrium and non-equilibrium optical properties of single-layer transition metal dichalcogenides (TMDs) are determined by strongly bound excitons. Exciton relaxation dynamics in TMDs have been extensively studied by time-domain optical spectroscopies. However, the formation dynamics of excitons following non-resonant photoexcitation of free electron-hole pairs have been challenging to directly probe because of their inherently fast timescales. Here, we use extremely short optical pulses to non-resonantly excite an electron-hole plasma and show the formation of two-dimensional excitons in single-layer MoS2 on the timescale of 30 fs via the induced changes to photo-absorption. These formation dynamics are significantly faster than in conventional 2D quantum wells and are attributed to the intense Coulombic interactions present in 2D TMDs. A theoretical model of a coherent polarization that dephases and relaxes to an incoherent exciton population reproduces the experimental dynamics on the sub-100-fs timescale and sheds light into the underlying mechanism of how the lowest-energy excitons, which are the most important for optoelectronic applications, form from higher-energy excitations. Importantly, a phonon-mediated exciton cascade from higher energy states to the ground excitonic state is found to be the rate-limiting process. These results set an ultimate timescale of the exciton formation in TMDs and elucidate the exceptionally fast physical mechanism behind this process.


2016 ◽  
Vol 93 (4) ◽  
Author(s):  
Akshay Singh ◽  
Galan Moody ◽  
Kha Tran ◽  
Marie E. Scott ◽  
Vincent Overbeck ◽  
...  

Nano Letters ◽  
2019 ◽  
Vol 19 (7) ◽  
pp. 4816-4816
Author(s):  
Alexander W. Bataller ◽  
Robert A. Younts ◽  
Avinash Rustagi ◽  
Yiling Yu ◽  
Hossein Ardekani ◽  
...  

Nano Letters ◽  
2019 ◽  
Vol 19 (2) ◽  
pp. 1104-1111 ◽  
Author(s):  
Alexander W. Bataller ◽  
Robert A. Younts ◽  
Avinash Rustagi ◽  
Yiling Yu ◽  
Hossein Ardekani ◽  
...  

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Abderrezak Torche ◽  
Gabriel Bester

AbstractTransition metal dichalcogenides monolayers host strongly bounded Coulomb complexes such as exciton and trion due to charge confinement and screening reduction in two dimensions. Biexciton, a bound state of two electrons and two holes, has also been observed in these materials with a binding energy which is one order of magnitude larger than its counterpart in conventional semiconductors. Here, using first principles methods, we address the biexciton in WSe2 monolayer and unravel the important role of the electron-hole exchange interaction in dictating the valley character of biexciton states and their fine structure. In particular, the fundamental biexciton transition which is located between the exciton and trion peaks is shown to have a fine structure of 2.8 meV mainly due to the splitting of the dark exciton state under the intervalley electron-hole exchange interaction. Non equilibrium effects are also addressed and optical fingerprints of non-thermalized biexciton population are discussed.


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