arXiv subjects

Kacper Walczyk

Publications and source records attributed to Kacper Walczyk.

3 recordsLinked to original sources

arXiv2026

Dopant-induced modifications of the optical properties of GaSe

Doping plays a crucial role in tailoring the electronic, optical, and magnetic properties of semiconductors, enabling control of carrier dynamics and the formation of functional states for optoelectronic applications. We investigate the influence of Fe dopants on the optical properties of GaSe crystals using photoluminescence (PL) spectroscopy under varying excitation power, temperature, and magnetic field. Fe incorporation introduces multiple sharp emission lines in addition to intrinsic excitonic transitions, including free and localised excitons. Power- and temperature-dependent measurements indicate that these emission features are associated with Fe-related dopant centres (Fe-bound excitons). Magneto-PL measurements reveal two distinct families of $g$-factors, enabling the identification of intrinsic excitonic transitions and Fe-induced defect states. These results demonstrate that Fe doping creates optically and magnetically active centres in GaSe, providing insight into defect-related excitonic processes and their potential relevance for magneto-optoelectronic and quantum photonic applications.

cond-mat.mtrl-sci↗

arXiv2026

Resonant Raman scattering in bilayer 3R-MoS$_{2}$

Raman scattering is a powerful spectroscopic technique widely employed to investigate light-matter interactions and lattice dynamics in two-dimensional materials. Here, we investigate the temperature-dependent resonant Raman response of bilayer 3R-MoS$_2$. The study combines multi-wavelength Raman spectroscopy, photoluminescence measurements, and density functional theory calculations to track the evolution of excitonic transitions and resonance conditions. We observe contributions from both zone-centre and finite-momentum phonons, a pronounced quenching of the Stokes intensity at low temperatures followed by saturation, the emergence of anti-Stokes scattering above 130~K, and a strong deviation of the effective phonon temperature from the lattice temperature induced by resonance effects. These results demonstrate that the Raman response is governed by the interplay between incoming and outgoing resonance processes, providing deeper insight into exciton-phonon coupling in van der Waals materials.

cond-mat.mtrl-sci↗

arXiv2026

Doping-Induced Brightening of Dark Excitons and Trions in a WSe$_2$ Monolayer

Optically dark excitonic states play a critical role in the valleytronic, electronic, and optical properties of monolayer semiconducting transition metal dichalcogenides. Here, we investigate how electrostatic doping affects the in-plane magnetic-field-induced activation of dark excitonic complexes in a gated WSe$_2$ monolayer. By continuously tuning the carrier density via gate voltage, we access $n$-type, charge-neutral, and $p$-type regimes and track the corresponding brightening dynamics. We find that the brightening rates of the dark negative trion ($T^{D-}$), dark neutral exciton ($X^{D}$), and dark positive trion ($T^{D+}$) exhibit a strong and nontrivial dependence on doping. In particular, the pronounced asymmetry in the brightening behaviour of the neutral $X^{D}$ complex and the charged $T^{D-}$ and $T^{D+}$ trions reveals distinct underlying carrier interactions, which we describe using a rate-equation model for their steady-state populations. These findings highlight the key role of dark excitonic complexes in governing the optical response and carrier dynamics of doped S-TMD monolayers.

cond-mat.mes-hall↗