arXiv subjects

Igor Antoniazzi

Publications and source records attributed to Igor Antoniazzi.

9 recordsLinked to original sources

arXiv2026

Non-trivial topological spin-polarized surface states induced nonreciprocal transport in the hourglass semimetal

Quantum materials such as topological semimetals have gained consummate interest due to their exotic band crossings and protected surface states. In particular, Ta$_3$GeTe$_6$ has emerged as a prototypical hourglass Dirac semimetal, as confirmed by both experimental and theoretical analysis. The ARPES confirms the topological hourglass-type band dispersions and Rashba-type band, while Hall measurements reveal a high hole carrier concentration and nonreciprocal transport behavior. These findings are further supported by a phenomenological toy model, which predicts a nonreciprocal resistance, consistent with the observed direction-dependent magnetoresistance. Furthermore, the Raman spectroscopy uncovers two-fold and four-fold phonon symmetries drag of highly anisotropic phonons, which establishes symmetry-dependent resistance. DFT calculations reveal Dirac-like and hourglass Dirac band crossings near the Fermi level for the bulk, with Rashba-type spin splitting induced by the surface inversion-symmetry breaking, leading to spin-polarized surface states. The combined experimental and theoretical results demonstrate that Ta$_3$GeTe$_6$ hosts a non-trivial electronic topology, with the inversion-symmetry breaking at the surface as the driver of this nonreciprocal transport behavior.

cond-mat.mtrl-sci↗

arXiv2026

Paramagnetic phase of MnTe$_2$: complete one phonon Raman spectrum

In this study we present a complete first-order Raman scattering spectrum of paramagnetic phase of MnTe$_2$- a material, where new type of spin texture induced by noncoplanar antiferromagnetic ordering below the Néel temperature ($T_N \approx 90$ K) gives rise to unconventional scenario of magnetism. Basic properties of all five phonon modes ($A_g$, $E_g$ and three $T_g$) predicted by the group theory have been successfully approached through polarization, excitation and temperature dependent measurements. In particular, the ever-missing phonon mode of $T_g$ symmetry has been unambiguously resolved in the room temperature Raman spectrum at approximately 107 cm$^{-1}$, just 1.5 cm$^{-1}$ higher in frequency compared to the $E_g$ mode. Density functional theory calculations reproduce the observed Raman-active phonon spectrum and support the assignment of all five first-order Raman modes, including the near-degeneracy of the $E_g$ and one of the $T_g$ vibrations. The calculations further reveal a dense manifold of low-energy antiferromagnetic spin configurations, separated from the ground state by only a few meV per formula unit. Furthermore, strong signals of inelastically scattered light from the paramagnetic (PM) phase of MnTe$_2$ were acquired with long wavelength excitations, i.e. 633 nm and 785 nm, revealing the $2A_g$ overtone at approx. 360 cm$^{-1}$. The enhanced absorption of the light in the near infrared range could be a putative reason behind the anomalous angular dependence of scattered intensity of the highest frequency $T_g$ phonon mode (183 cm$^{-1}$) measured in PM MnTe$_2$ with parallelly aligned polarizers. Finally, upon cooling just below the $T_N$, the measured properties of phonons remained basically unperturbed by the incipient long-range antiferromagnetic ordering.

cond-mat.mtrl-sci↗

arXiv2026

Strong Spin-Lattice Interaction in Layered Antiferromagnetic CrCl$_\textrm{3}$

Understanding the coupling between lattice vibrations and magnetic order is crucial for controlling properties of two-dimensional magnetic materials. Here, we investigate the vibrational properties of bulk and thick-flake CrCl$_\textrm{3}$ using polarization-resolved Raman spectroscopy, complemented by photoluminescence, photoluminescence excitation, and optical absorption measurements. Symmetry analysis, supported by first-principles phonon calculations, enables the unambiguous assignment of all eight Raman-active modes, four $\textrm{A}_\textrm{g}$ and four $\textrm{E}_\textrm{g}$, previously predicted only theoretically. Excitation-energy-dependent measurements reveal that the strong enhancement of selected phonon modes originates primarily from interference effects rather than resonant Raman scattering. Temperature-dependent Raman spectroscopy further reveals pronounced signatures of spin-phonon coupling across the transition from a fully antiferromagnetic phase, through an intermediate regime with local, domain-like ferromagnetic order, to the paramagnetic phase, accompanied by a clear rhombohedral-to-monoclinic structural transition. Together, these results demonstrate how lattice, electronic, and magnetic degrees of freedom collectively govern the Raman response of CrCl$_\textrm{3}$.

cond-mat.mtrl-sci↗

arXiv2025

Extremely high excitonic $g$-factors in 2D crystals by alloy-induced admixing of band states

Monolayers (MLs) of semiconducting transition metal dichalcogenides (\mbox{S-TMDs}) emit light very efficiently and display rich spin-valley physics, with gyromagnetic ($g$-) factors of about -4. Here, we investigate how these properties can be tailored by alloying. Magneto-optical spectroscopy is used to reveal the peculiar properties of excitonic complexes in Mo$_{x}$W$_{1-x}$Se$_2$ MLs with different Mo and W concentrations. We show that the alloys feature extremely high $g$-factors for neutral excitons, that change gradually with the composition up to reaching values of the order of -10 for $x \approx 0.2$. First-principles calculations corroborate the experimental findings and provide evidence that alloying in S-TMDs results in a non-trivial band structure engineering, being at the origin of the high $g$-factors. The theoretical framework also suggests a higher strain sensitivity of the alloys, making them promising candidates for tailor-made optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Magneto-Excitonic Duality From Monolayer to Trilayer CrSBr

Two-dimensional (2D) layered magnetic materials (LMMs) are a newly emerging class of van der Waals materials, opening new opportunities to study magneto-excitonic coupling. The air-stable, structurally and optically anisotropic A-type antiferromagnetic chromium sulfur bromide (CrSBr) is one of the most prominent examples of such LMMs. We investigate photoluminescence (PL) and PL excitation of mono- to tri-layers CrSBr and find that it exhibits a unique duplexity, supporting both Frenkel- and Wannier-Mott-like excitons. Our magneto-optical experiments reveal a similar excitonic response from the mono- and trilayer systems and a completely different signature in the bilayer flake. This shows a different origin of the low-lying excitonic species (A, A', and B) in the band structure. We confirm the robustness of the magneto-excitonic coupling in few-layer CrSBr. Our work enables a more comprehensive exploration of the dual excitonic behavior in 2D materials.

cond-mat.mtrl-sci↗

arXiv2024

Pressure-induced optical anisotropy of HfS$_2$

The effect of pressure on Raman scattering (RS) in the bulk HfS$_2$ is investigated under hydrostatic and non-hydrostatic conditions. The RS lineshape does not change significantly in the hydrostatic regime, showing a systematic blueshift of the spectral features. In a non-hydrostatic environment, seven peaks emerge in the spectrum ($P$=7 GPa) dominating the lineshape up to $P$=10.5 GPa. The change in the RS lineshape manifests a pressure-induced phase transition in HfS$_2$. The simultaneous observation of both low-pressure (LP) and high-pressure (HP) related RS peaks suggests the corresponding coexistence of two different phases over a large pressure range. We found that the HP-related phase is metastable, persisting during the decompression cycle down to $P$=1.2 GPa with the LP-related features finally recovering at even lower pressures. The angle-resolved polarized RS (ARPRS) performed under $P$=7.4 GPa revealed a strong in-plane anisotropy of both the LP-related A$_{1g}$ mode and the HP peaks. The anisotropy is related to the possible distortion of the structure induced by the non-hydrostatic component of the pressure. We describe the obtained results by the influence of the non-hydrostatic pressure on the observed phase transition. We interpret our results in terms of a distorted $Pnma$ phase as a possible HP induced structure of HfS$_2$.

cond-mat.mtrl-sci↗

arXiv2023

Ion-beam-milled graphite nanoribbons as mesoscopic carbon-based polarizers

We demonstrate optical reflectivity and Raman responses of graphite microstructures as a function of light polarization when the incident light is applied perpendicular to the material's stacking direction (c-axis). For this, we employed novel graphite nanoribbons with edges polished through ion-beam etching. In this unique configuration, a strong polarization dependence of the D, G, and 2D Raman modes is observed. At the same time, polarized reflectivity measurements demonstrate the potential of such a device as a carbon-based, on-chip polarizer. We discuss the advantages of the proposed fabrication method as opposed to the mechanical polishing of bulk crystals.

cond-mat.mes-hall↗

arXiv2023

Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower-to-Higher Bandgap 2D Material

High light absorption (~15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenide (TMD) make it an ideal candidate for optoelectronic applications. Competing interlayer charge (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe2-to-MoS2 with an interlayer hBN, due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.

cond-mat.mtrl-sci↗

arXiv2022

The effect of temperature and excitation energy on Raman scattering in bulk HfS$_2$

Raman scattering (RS) in bulk hafnium disulfide (HfS$_2$) is investigated as a function of temperature (5 K $-$ 350 K) with polarization resolution and excitation of several laser energies. An unexpected temperature dependence of the energies of the main Raman-active (A$_{\textrm{1g}}$ and E$_{\textrm{g}}$) modes with the temperature-induced blueshift in the low-temperature limit is observed. The low-temperature quenching of a mode $ω_1$ (134 cm$^{-1}$) and the emergence of a new mode at approx. 184 cm$^{-1}$, labeled Z, is reported. The optical anisotropy of the RS in HfS$_2$ is also reported, which is highly susceptible to the excitation energy. The apparent quenching of the A$_{\textrm{1g}}$ mode at $T$=5 K and of the E$_{\textrm{g}}$ mode at $T$=300 K in the RS spectrum excited with 3.06~eV excitation is also observed. We discuss the results in the context of possible resonant character of light-phonon interactions. Analyzed is also a possible effect of the iodine molecules intercalated in the van der Waals gaps between neighboring HfS$_2$ layers, which inevitably result from the growth procedure.

cond-mat.mes-hall↗