arXiv subjects

Matěj Velický

Publications and source records attributed to Matěj Velický.

7 recordsLinked to original sources

arXiv2026

Three-dimensional excitonic dipole anisotropy enables ultrabroadband polarization photodetection in CrCl3

Simultaneous detection of the spectral and polarization properties of light is highly desirable for integrated imaging and photonic technologies but typically requires complex multi-component architectures. Here, we demonstrate that the intrinsic dielectric anisotropy of layered insulating CrCl3 enables ultrabroadband polarization-resolved photodetection spanning wavelengths from 300 to 1700 nm. The photoresponse is governed by long-lived ligand-field excitons, whose microsecond-scale lifetime produces a photoconductive gain exceeding 4.5 x 10^4. By combining wavelength-, polarization-, and angle-resolved optoelectronic measurements, we reveal that distinct ligand-field and higher-energy excitonic transitions possess different optical dipole orientations, leading to excitation-energy-dependent rotation of the in-plane polarization axis. Furthermore, oblique illumination activates out-of-plane optical dipoles, while competing excitonic transitions with distinct dipole orientations drive wavelength-dependent rotation and reversal of the polarization anisotropy. Together, these effects produce a highly tunable degree of polarization ranging from -90% to +75%, establishing intrinsic three-dimensional vectorial light-matter interactions in a layered magnetic van der Waals insulator. These findings establish dielectric anisotropy and excitonic dipole engineering as powerful design principles for compact ultrabroadband polarization-sensitive photodetectors and multifunctional van der Waals photonic systems.

physics.optics↗

arXiv2026

Interplay of Cl Substitution and He$^{+}$ Irradiation in CrSBr$_{1-x}$Cl$_{x}$

Two-dimensional magnetic semiconductors provide a promising platform for exploring the interplay between disorder, lattice dynamics, and resonant light--matter interactions. Among them, CrSBr exhibits strong in-plane anisotropy and pronounced resonance-enhanced Raman scattering. Here, we investigate the effects of Cl substitution and He$^{+}$ irradiation on the vibrational response of CrSBr using polarization-resolved Raman spectroscopy. Cl substitution activates additional phonon modes associated with local symmetry breaking, while He$^{+}$ irradiation introduces distinct defect-related scattering channels and enhanced phonon broadening. The combined effects of alloy disorder and externally introduced defects lead to strong anisotropic reconstruction of the Raman spectra and modification of the nonlinear Raman response under near-resonant 1.96 eV excitation. Power-dependent measurements reveal robust superlinear scaling of both intrinsic and substitution-induced phonon modes, indicating persistent resonance-enhanced electron--phonon coupling even in defect-engineered samples.

cond-mat.mes-hall↗

arXiv2026

Robust phonon engineering and symmetry-selective lattice dynamics in CrSBr$_{1-x}$Cl$_{x}$

Atomic substitution provides a controlled route to engineer lattice dynamics in low-symmetry two-dimensional materials. Here, by combining polarization-resolved Raman spectroscopy and first-principles calculations, we investigate the evolution of phonon characteristics in CrSBr$_{1-x}$Cl$_{x}$ ($0 \leq x \leq \sim 0.5$) upon partial substitution of Br with Cl atoms. Progressive Cl substitution of Br induces systematic shifts of parent CrSBr out-of-plane $A_\textrm{g}$ phonon modes and activates additional Raman features. These features persist across different polarization configurations and excitation energies, reflecting substitution-induced symmetry lowering and local lattice perturbations. Explicit supercell phonon calculations combined with Raman $Γ$-density-of-states simulations identify these features as symmetry-lowered descendants of parent modes arising from alloy disorder. Complementary strain-dependent calculations reveal that anisotropic lattice compression plays a key role in renormalizing Cr-S dominated phonons. Under near-resonant excitation, stimulated Raman scattering-like amplification remains observable with increasing Cl content, highlighting the resilience of anisotropic electron-phonon coupling in this system.

cond-mat.mtrl-sci↗

arXiv2025

Resonance Raman Scattering and Anomalous Anti-Stokes Phenomena in CrSBr

CrSBr, a van der Waals material, stands out as an air-stable magnetic semiconductor with appealing intrinsic properties such as crystalline anisotropy, quasi-1D electronic characteristics, layer-dependent antiferromagnetism, and non-linear optical effects. In this study, we investigate the differences between the absorption and emission spectra, focusing on the origin of the emission peak near 1.7 eV observed in the photoluminescence spectrum of CrSBr. Our findings are corroborated by excitation-dependent Raman experiments. Additionally, we explore the anti-Stokes Raman spectra and observe an anomalously high anti-Stokes to Stokes intensity ratio of up to 0.8, which varies significantly with excitation laser power and crystallographic orientation relative to the polarization of the scattered light. This ratio is notably higher than that observed in graphene ($\approx$ 0.1) and MoS$_2$ ($\approx$ 0.4), highlighting the unique vibrational and electronic interactions in CrSBr. Lastly, we examine stimulated Raman scattering and calculate the Raman gain in CrSBr, which attains a value of 1 $\times$ 10$^{8}$ cm/GW, nearly four orders of magnitude higher than that of previously studied three-dimensional systems.

cond-mat.mes-hall↗

arXiv2024

Strain-Induced Decoupling Drives Gold-Assisted Exfoliation of Large-Area Monolayer 2D Crystals

Gold assisted exfoliation (GAE) is a groundbreaking mechanical exfoliation technique, producing centimeter scale single crystal monolayers of 2D materials. Such large, high quality films offer unparalleled advantages over the micron sized flakes typically produced by conventional exfoliation techniques, significantly accelerating the research and technological advancements in the field of 2D materials. Despite its wide applications, the fundamental mechanism of GAE remains poorly understood. In this study, using MoS2 on Au as a model system, we employ ultralow frequency Raman spectroscopy to elucidate how the interlayer interactions within MoS2 crystals are impacted by the gold substrate. The results reveal that the coupling at the first interface between the adhered layer on the gold substrate and the adjacent layer, is substantially weakened, with the binding force being reduced to nearly zero. This renders the first interface the weakest point in the system, thereby the crystal preferentially cleaves at this junction, generating large area monolayers with sizes comparable to the parent crystal. Biaxial strain in the adhered layer, induced by the gold substrate, is identified as the driving factor for the decoupling effect. We establish the strain-induced decoupling effect as the primary mechanism of GAE, which could also play a significant role in general mechanical exfoliations.

cond-mat.mtrl-sci↗

arXiv2018

Hunting micrometer-sized graphene flakes on gold substrate

Gold is widely used as the substrate material in many graphene devices, due to its superior optoelectronic properties and chemical stability. However, there has been little experimental investigation on the optical contrast of graphene films on Au substrates. Here we report accurate measurement of the optical contrast spectra of few-layer graphene flakes on bulk Au. We used a high-resolution optical microscopy with a 100x magnification objective, accurately determining the thickness of flakes as small as one micrometer in lateral size, which are highly desired in many applications. The results are in excellent agreement with theoretical calculations and confirmed by Raman and AFM measurements. Furthermore, we demonstrate that the optical contrast spectroscopy is sensitive enough to detect the adsorption of a sub-monolayer airborne hydrocarbon molecules, which can reveal whether graphene is con-taminated and opens the opportunity to develop miniaturized and ultrasensitive molecular sensors.

cond-mat.mtrl-sci↗

arXiv2016

Phase segregation facilitates exfoliation of franckeite crystals to a single unit cell thickness

Weak interlayer van der Waals interactions in bulk crystals facilitate their mechanical exfoliation to monolayer and few-layer two-dimensional (2D) materials, which exhibit striking physical phenomena absent in their bulk form. Here we study a 2D form of a mineral franckeite and show that phase segregation into discrete layers at the sub-nanometre scale facilitates its layered structure and basal cleavage. This behaviour is likely to be common in a wider family of complex crystals and could be exploited for a single-step synthesis of van der Waals heterostructures, as an alternative to stacking of 2D materials. Mechanical exfoliation allowed us to produce crystals down to a single unit cell thickness and rationalise its basal cleavage by atomic-resolution scanning transmission electron microscopy (STEM). We demonstrate p-type electrical conductivity and remarkable electrochemical properties in exfoliated crystals, which shows promise for energy storage applications.

cond-mat.mes-hall↗