arXiv subjects

E. Katsipoulaki

Publications and source records attributed to E. Katsipoulaki.

3 recordsLinked to original sources

arXiv2026

Dipolar interlayer excitons in transition metal dichalcogenide alloy heterobilayers

Interlayer excitons in transition metal dichalcogenide (TMD) heterobilayers possess a permanent electric dipole moment and long recombination lifetimes, making them a promising platform for exploring excitonic many-body physics. Here, we report dipolar interlayer excitons in a MoS$_{1.4}$Se$_{0.6}$/MoSe$_2$ heterobilayer encapsulated in hexagonal boron nitride. Low-temperature photoluminescence measurements reveal a distinct emission peak at $\sim1.4$ eV, attributed to radiative recombination of interlayer excitons. The emission exhibits a blueshift with increasing excitation power, indicating repulsive dipole-dipole interactions. Time-resolved photoluminescence measurements uncover nanosecond-scale lifetimes, consistent with the spatial separation of electrons and holes across the two layers. These findings establish chalcogen-alloyed TMD heterobilayers as a versatile platform for engineering dipolar excitons and tuning excitonic interactions in van der Waals materials.

cond-mat.mes-hall↗

arXiv2025

Spin-valley polarization control in WSe$_2$ monolayers using photochemical doping

We report on the influence of a photochemical doping method on the spin-valley polarization degree ($P_{c}$) of excitons in WSe$_2$ monolayers. By varying the carrier density and transitioning from an excess of electrons (n-type) to an excess of holes (p-type), we observe a non-monotonic dependence of $P_{c}$ on the doping level. Using controlled, single-shot photochlorination steps, we unveil this non-monotonic behavior, with $P_{c}$ reaching a minimum value of less than 10$\%$ at 78 K near the charge neutrality point, while increasing by a factor of three at a hole density of $5 \times 10^{11} \,\mathrm{cm^{-2}}$. The impact of the doping on $P_{c}$ is explained using a phenomenological model that accounts for various mechanisms influencing exciton polarization dynamics, including exciton-carrier scattering processes and exciton-to-trion conversion rates. Among these, exciton-carrier collisions emerge as the dominant mechanism driving the observed variations in $P_{c}$, while the exciton effective lifetime remains nearly independent of doping. These findings highlight the potential of photochemical methods for investigating valley physics and for effectively tuning the exciton polarization degree in transition metal dichalcogenide monolayers.

cond-mat.mes-hall↗

arXiv2023

Electron density control in tungsten diselenide monolayers via photochlorination

Modulation of the Fermi level using an ultraviolet (UV)-assisted photochemical method is demonstrated in tungsten diselenide monolayers. Systematic shifts and relative intensities between charged and neutral exciton species indicate a progressive and controllable decrease of the electron density and switch tungsten diselenide from n-type to a p-type semiconductor. The presence of chlorine in the 2D crystal shifts the Fermi level closer to the valence band while the effect can be only partially reversible via continuous wave laser rastering process. The presence of chlorine species in the lattice is validated by X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations predict that adsorption of chlorine on the selenium vacancy sites leads to p-type doping. The results of our study indicate that photochemical techniques have the potential to enhance the performance of various 2D materials, making them suitable for potential applications in optoelectronics.

cond-mat.mtrl-sci↗