arXiv subjects

Bala Murali Krishna Mariserla

Publications and source records attributed to Bala Murali Krishna Mariserla.

4 recordsLinked to original sources

arXiv2025

Reversible Excitonic Charge State Conversion and High Quasiparticle Densities in PVA-doped Monolayer WS$_2$ on 2D Microsphere Array

Controllable quasiparticle radiation in two-dimensional (2D) semiconductors is essential for efficient carrier recombination, tunable emission, and modulation of valley polarization which are strongly determined by both the density and nature of underlying excitonic species. Conventional chemical doping techniques, however, often hinder the reversibility and density of excitonic charge states (exciton and trion) due to unfavorable interactions between dopant and 2D materials. In this work, efficient excitonic charge state conversion is achieved by doping monolayer WS$_2$ using water rinsed PVA and the quasiparticle densities are further enhanced by applying high periodic biaxial strain (up to 2.3%) through a 2D silica microsphere array. The method presented here enables nearly 100% reversible trion-to-exciton conversion without the need of electrostatic gating, while delivering thermally stable trions with a large binding energy of ~56 meV and a high free electron density of ~3$\times$10$^{13}$ cm$^{-2}$ at room temperature. Strain-induced funneling of the PVA-injected free electrons substantially increases the excitonic quasiparticle densities and boosts the trion emission by 41%. Overall, this approach establishes a versatile platform for excitonic charge state conversion and enhanced quasiparticle density in 2D materials, offering promising opportunities for future optical data storage, quantum-light and display technologies.

cond-mat.mes-hall↗

arXiv2024

Unconventional optical response in monolayer graphene upon dominant intraband scattering

Scattering dynamics influence the graphenes transport properties and inhibits the charge carrier deterministic behaviour. The intra or inter-band scattering mechanisms are vital for graphenes optical conductivity response under specific considerations of doping. Here, we investigated the influence of scattering systematically on optical conductivity using a semi-classical multiband Boltzmann equation with inclusion of both electron-electron $\&$ electron-phonon collisions. We found unconventional characteristics of linear optical response with a significant deviation from the universal conductivity $\frac{e^2}{4\hbar}$ in doped monolayer graphene. This is explained through phenomenological relaxation rates under low doping regime with dominant intraband scattering. Such novel optical responses are vanished at high temperatures or overdoping conditions due to strong Drude behaviour. With the aid of approximations around Dirac points we have developed analytical formalism for many body interactions and is in good agreement with the Kubo approaches.

cond-mat.mes-hall↗

arXiv2023

Tuning electronic properties in transition metal dichalcogenides MX$_2$ (M= Mo/W, X= S/Se) heterobilayers with strain and twist angle

We explore the direct to indirect band gap transitions in MX$_2$ (M= Mo/W, X= S/Se) transition metal dichalcogenides heterobilayers for different system compositions, strains, and twist angles based on first principles density functional theory calculations within the G$_0$W$_0$ approximation. The obtained band gaps that typically range between 1.4$-$2.0 eV are direct/indirect for different/same chalcogen atom systems and can often be induced through expansive/compressive biaxial strains of a few percent. A direct to indirect gap transition is verified for heterobilayers upon application of a finite 16$^{\circ}$ twist that weakens interlayer coupling. The large inter-layer exciton binding energies of the order of $\sim$~250~meV estimated by solving the Bethe-Salpeter equation suggest these systems are amenable to be studied through infrared and Raman spectroscopy.

cond-mat.mtrl-sci↗

arXiv2020

Directly visualizing the momentum forbidden dark excitons and their dynamics in atomically thin semiconductors

Resolving the momentum degree of freedom of excitons - electron-hole pairs bound by the Coulomb attraction in a photoexcited semiconductor, has remained a largely elusive goal for decades. In atomically thin semiconductors, such a capability could probe the momentum forbidden dark excitons, which critically impact proposed opto-electronic technologies, but are not directly accessible via optical techniques. Here, we probe the momentum-state of excitons in a WSe2 monolayer by photoemitting their constituent electrons, and resolving them in time, momentum and energy. We obtain a direct visual of the momentum forbidden dark excitons, and study their properties, including their near-degeneracy with bright excitons and their formation pathways in the energy-momentum landscape. These dark excitons dominate the excited state distribution - a surprising finding that highlights their importance in atomically thin semiconductors.

cond-mat.mtrl-sci↗