scholarly journals Direct Measurement of Biexcitons in Monolayer WS2

2D Materials ◽  
2021 ◽  
Author(s):  
Mitchell A Conway ◽  
Jack B Muir ◽  
Stuart K Earl ◽  
Matthias Wurdack ◽  
Rishabh Mishra ◽  
...  
Keyword(s):  
Binding Energy ◽  
Transition Metal Dichalcogenides ◽  
Exciton State ◽  
Energy Difference ◽  
Doubly Excited States ◽  
Doubly Excited ◽  
Spectral Peaks ◽  
Metal Dichalcogenides ◽  
Biexciton Binding Energy ◽  
Definition Of

Abstract The optical properties of atomically thin transition metal dichalcogenides (TMDCs) are dominated by Coulomb bound quasi-particles, such as excitons, trions, and biexcitons. Due to the number and density of possible states, attributing different spectral peaks to the specific origin can be difficult. In particular, there has been much conjecture around the presence, binding energy and/or nature of biexcitons in these materials. In this work, we remove any ambiguity in identifying and separating the optically excited biexciton in monolayer WS2 using two-quantum multidimensional coherent spectroscopy (2Q-MDCS), a technique that directly and selectively probes doubly-excited states, such as biexcitons. The energy difference between the unbound two-exciton state and the biexciton is the fundamental definition of biexciton binding energy and is measured to be 26 ± 2 meV. Furthermore, resolving the biexciton peaks in 2Q-MDCS allows us to identify that the biexciton observed here is composed of two bright excitons in opposite valleys.

scholarly journals Biexcitons fine structure and non-equilibrium effects in transition metal dichalcogenides monolayers from first principles

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Abderrezak Torche ◽  
Gabriel Bester
Keyword(s):  
Fine Structure ◽  
Transition Metal ◽  
Exchange Interaction ◽  
First Principles ◽  
Transition Metal Dichalcogenides ◽  
Exciton State ◽  
Two Dimensions ◽  
Electron Hole ◽  
Metal Dichalcogenides ◽  
Non Equilibrium

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.

scholarly journals Efficient phonon cascades in WSe2 monolayers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ioannis Paradisanos ◽  
Gang Wang ◽  
Evgeny M. Alexeev ◽  
Alisson R. Cadore ◽  
Xavier Marie ◽  
...  
Keyword(s):  
Excitation Energy ◽  
Laser Excitation ◽  
Transition Metal Dichalcogenides ◽  
Exciton State ◽  
Strong Temperature Dependence ◽  
Cascade Process ◽  
Photoluminescence Intensity ◽  
Tungsten Diselenide ◽  
Carrier Relaxation ◽  
Metal Dichalcogenides

AbstractEnergy relaxation of photo-excited charge carriers is of significant fundamental interest and crucial for the performance of monolayer transition metal dichalcogenides in optoelectronics. The primary stages of carrier relaxation affect a plethora of subsequent physical mechanisms. Here we measure light scattering and emission in tungsten diselenide monolayers close to the laser excitation energy (down to ~0.6 meV). We reveal a series of periodic maxima in the hot photoluminescence intensity, stemming from energy states higher than the A-exciton state. We find a period ~15 meV for 7 peaks below (Stokes) and 5 peaks above (anti-Stokes) the laser excitation energy, with a strong temperature dependence. These are assigned to phonon cascades, whereby carriers undergo phonon-induced transitions between real states above the free-carrier gap with a probability of radiative recombination at each step. We infer that intermediate states in the conduction band at the Λ-valley of the Brillouin zone participate in the cascade process of tungsten diselenide monolayers. This provides a fundamental understanding of the first stages of carrier–phonon interaction, useful for optoelectronic applications of layered semiconductors.

scholarly journals 2D Nanomaterial-Based Surface Plasmon Resonance Sensors for Biosensing Applications

Micromachines ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 779
Author(s):  
Sachin Singh ◽  
Pravin Kumar Singh ◽  
Ahmad Umar ◽  
Pooja Lohia ◽  
Hasan Albargi ◽  
...  
Keyword(s):  
Surface Plasmon Resonance ◽  
Binding Energy ◽  
Surface Plasmon ◽  
Plasmon Resonance ◽  
Transition Metal Dichalcogenides ◽  
Characteristic Parameters ◽  
Kretschmann Configuration ◽  
Spr Sensor ◽  
Metal Dichalcogenides ◽  
2D Nanomaterials

The absorption and binding energy of material plays an important role with a large surface area and conductivity for the development of any sensing device. The newly grown 2D nanomaterials like black phosphorus transition metal dichalcogenides (TMDCs) or graphene have excellent properties for sensing devices’ fabrication. This paper summarizes the progress in the area of the 2D nanomaterial-based surface plasmon resonance (SPR) sensor during last decade. The paper also focuses on the structure of Kretschmann configuration, the sensing principle of SPR, its characteristic parameters, application in various fields, and some important recent works related to SPR sensors have also been discussed, based on the present and future scope of this field. The present paper provides a platform for researchers to work in the field of 2D nanomaterial-based SPR sensors.

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