arXiv subjects

Yaron Amouyal

Publications and source records attributed to Yaron Amouyal.

15 recordsLinked to original sources

arXiv2026

Tellurium sublattice instability driven amorphization in the chalcogenide AgSbTe2 under pressure

Pressure provides a powerful thermodynamic route to access hidden structural states in functional materials, yet the microscopic origin of pressure-induced amorphization remains elusive in many complex chalcogenides. Here we report a detailed high-pressure structural study of AgSbTe2,combining synchrotron X-ray diffraction with density functional theory and molecular dynamics calculations up to 60 GPa. We uncover a pressure-driven transformation from the ambient R-3m phase to a fully disordered cubic Im3m phase, through an extended intermediate amorphous state. Enthalpy calculations reveal a near-degeneracy between the R3m and Im3m structures over a broad pressure range, dictating amorphization. Contrary to previously speculated cation vacancies, the amorphization is governed by a pronounced displacement instability of the Te sublattice. Remarkably, the time dependent decompression pathway controls the final structural state, resulting in either amorphous (slow decompression) or fully crystalline (fast decompression) states, indicative of a strong counterintuitive kinetic effect.

cond-mat.mtrl-sci↗

arXiv2026

Evidence for Many-Body States in NiPS$_3$ Revealed by Angle-Resolved Photoelectron Spectroscopy

We present $μ$-ARPES spectra of the Mott-insulating van der Waals antiferromagnet NiPS$_3$. Signatures of strong correlations -- such as the onset of atomic or atomic-ligand multiplets and spin-orbit-entangled exciton have been observed in this material by various two-particle spectroscopies, but not previously in photoemission. Our measurements reveal a weakly dispersive feature at the valence-band edge that is absent in DFT+$U$ calculations and remains unchanged across the Néel transition. After critically examining and ruling out alternative interpretations, we show that an exact diagonalization of a NiS$_6$ cluster yields low-energy final-state configurations of mixed multiplet $d^7$ and $d^8\underline{L}$ character, whose energy differences are consistent with the observed additional feature. This implies that ARPES directly accesses local Ni-S multiplet physics in NiPS$_3$, revealing a many-body structure beyond mean-field theory. Our results confirm that NiPS$_3$ is an excellent model platform in which strong correlations, reduced dimensionality, and covalent metal-ligand bonding jointly shape both two- and single-particle spectroscopies, underscoring the need for a genuinely quantum many-body description of two-dimensional quantum materials.

cond-mat.str-el↗

arXiv2026

Crystal Anisotropy Implications on the Magneto-Optical Properties of van der Waals FePS3

Antiferromagnetic FePS3 has recently gained significant interest in its potential applications in spin-related devices. Here, we show that in-plane structural anisotropy has a major impact in shaping the optical responses of FePS3 single-crystals from the bulk form down to the monolayer limit. X-ray diffraction on a bulk FePS3 crystal confirms a distorted FeS6 octahedron causing inequivalent Fe-Fe distances and consequently resulting in a higher a/b lattice parameter ratio. Micro-photoluminescence observations on bulk and monolayer FePS3 reveal four emissions: one intra-atomic d-d transition (band A, centered at ~1.24 eV) and three p-d charge transfer transitions (bands B, C, and D, centered around ~1.79 eV, ~2.3 eV, and ~2.56 eV, respectively). These bands exhibit different polarization behaviors, which persist down to the monolayer limit. Density functional theory calculations from bulk to monolayer FePS3 reveal the underlying electronic structure, assign the observed emissions, and indicate why these peaks have contrasting linear and circular polarization responses. These results establish a direct structure-optics relation in FePS3, highlighting the strong coupling between lattice anisotropy, electronic transitions, and symmetry-selective optical selection rules.

cond-mat.mtrl-sci↗

arXiv2026

Modeling the Thermal Behavior of Photopolymers for In-Space Fabrication

Future long-duration space missions will require in-situ, on-demand manufacturing of tools and components. Photopolymer-based processes are attractive for this purpose due to their low energy requirements, volume efficiency, and precise control of curing. However, photopolymerization generates significant heat, which is difficult to regulate in microgravity where natural convection is absent, leading to defects such as surface blistering and deformation. In this work, we combine experimental studies and modeling to address these thermal challenges. We report results from International Space Station (ISS) experiments and a dedicated parabolic flight campaign, which confirm that suppressed convective heat transfer in microgravity exacerbates thermal buildup and defect formation. Building on these observations, we present a predictive thermal model that couples heat transfer, light absorption, and evolving material properties to simulate polymerization and temperature evolution under terrestrial and microgravity conditions. Laboratory validation demonstrates strong agreement between model predictions and measured temperature profiles. Applying the model to the ISS experiments, we show that the model accurately reproduces experimentally observed blistering in TJ-3704A, a commercial acrylate-based polymer resin, while also predicting defect-free outcomes for Norland optical adhesives. The model functions as a design tool for defect-free in-space manufacturing, enabling selection of polymer properties, exposure strategies, and environmental conditions that together inhibit excess thermal buildup, paving the way for scalable, reliable in-situ manufacturing during future missions.

cond-mat.mtrl-sci↗

arXiv2026

Probing the band structure of the strongly correlated antiferromagnet NiPS3 across its phase transition

NiPS3 is an exfoliable van-der-Waals intralayer antiferromagnet with zigzag-type spin arrangement. It is distinct from other TMPS3 (TM: transition metal) materials by optical excitations into a strongly correlated state that is tied to the magnetic properties. However, the related, fundamental band structure across the antiferromagnetic phase transition has not been probed yet. Here, we use angular-resolved photoelectron spectroscopy with μm resolution in combination with DFT+U calculations for that purpose. We identify a characteristic band shift across TN. It is attributed to bands of mixed Ni and S character related to the superexchange interaction of Ni 3t2g orbitals. Moreover, we find a structure above the valence band maximum with little angular dispersion that could not be reproduced by the calculations. The discrepancy suggests the influence of many-body interactions beyond the DFT+U approximations in striking contrast to the results on MnPS3 and FePS3, where these calculations were sufficient for an adequate description.

cond-mat.str-el↗

arXiv2025

On the ambient conditions crystal structure of AgSbTe2

We present a combined X-ray and neutron diffraction, Raman spectroscopy, and 121Sb NMR studies of AgSbTe2, supported by first-principles calculations aiming to elucidate its crystal structure. While diffraction methods cannot unambiguously resolve the structure, Raman and NMR data, together with electric field gradient calculations, strongly support the rhombohedral R-3m phase. Moreover, the agreement between experimental and calculated Raman spectra further corroborates this result, resolving the 60-year sold debate about the exact crystal structure of the AgSbTe2 compound.

cond-mat.mtrl-sci↗

arXiv2025

Comparative high-pressure structural and electrical transport properties study of thermoelectric (Bi1-xSbx)2Te3 compounds

Thermoelectric (Bi1-x Sbx)2Te3 (BST-x) compounds with x=0.2, 0.7 and 0.9 have been studied using synchrotron angle-dispersive powder x-ray diffraction in a diamond anvil cell up to 25 GPa (at room temperature). The results clearly indicate that all compounds of this study follow a similar structural evolution with the one of pure Bi2Te3 and Sb2Te3 under pressure. From the comparison between the critical pressures of the corresponding phase transitions, a clear trend of increasing critical pressure for the transition to the disordered solid-solution BCC phase was observed with the increase of Sb concentration. In the case of the BST-0.7, an extended stability of the solid-solution BCC phase up to, at least, 180 GPa was observed. Finally, electrical transport properties measurements under pressure for BST-0.7, document a reversible pressure-induced metallization above 12 GPa.

cond-mat.mtrl-sci↗

arXiv2024

Change in Magnetic Order in NiPS3 Single Crystals Induced by a Molecular Intercalation

Intercalation is a robust method for tuning the physical properties of a vast number of van der Waals (vdW) materials. However, the prospects of using intercalation to modify magnetism in vdWs systems and the associated mechanisms have not been investigated adequately. In this work, we modulate magnetic order in an XY antiferromagnet NiPS3 single crystals by introducing pyridine molecules into the vdWs gap under different thermal conditions. X-ray diffraction measurements indicated pronounced changes in the lattice parameter beta, while magnetization measurements at in-plane and out-of-plane configurations exposed reversal trends in the crystals Neel temperatures through intercalation-de-intercalation processes. The changes in magnetic ordering were also supported by three-dimensional thermal diffusivity experiments. The preferred orientation of the pyridine dipoles within vdW gaps was deciphered via polarized Raman spectroscopy. The results highlight the relation between the preferential alignment of the intercalants, thermal transport, and crystallographic disorder along with the modulation of anisotropy in the magnetic order. The theoretical concept of double-exchange interaction in NiPS3 was employed to explain the intercalation-induced magnetic ordering. The study uncovers the merit of intercalation as a foundation for spin switches and spin transistors in advanced quantum devices.

cond-mat.mtrl-sci↗

arXiv2024

Identifying band structure changes of FePS3 across the antiferromagnetic phase transition

Magnetic 2D materials enable novel tuning options of magnetism. As an example, the van der Waals material FePS3, a zigzag-type intralayer antiferromagnet, exhibits very strong magnetoelastic coupling due to the different bond lengths along different ferromagnetic and antiferromagnetic coupling directions enabling elastic tuning of magnetic properties. The likely cause of the length change is the intricate competition between direct exchange of the Fe atoms and superexchange via the S and P atoms. To elucidate this interplay, we study the band structure of exfoliated FePS3 by mu m scale ARPES (Angular Resolved Photoelectron Spectroscopy), both, above and, for the first time, below the Neel temperature TN. We find three characteristic changes across TN. They involve S 3p-type bands, Fe 3d-type bands and P 3p-type bands, respectively, as attributed by comparison with density functional theory calculations (DFT+U). This highlights the involvement of all the atoms in the magnetic phase transition providing independent evidence for the intricate exchange paths.

cond-mat.mtrl-sci↗

arXiv2024

Direct Optical Probing of the Magnetic Properties of the Layered Antiferromagnet CrPS$_4$

Unusual magnetic properties of Van der Waals type antiferromagnetic semiconductors make them highly attractive for spintronics and optoelectronics. A link between the magnetic and optical properties of those materials, required for practical applications, has not been, however, established so far. Here, we report on a combined experimental and theoretical study of magnetic, optical, and structural properties of bulk CrPS$_{4}$ samples. We find that the magnetic-field-dependent circular polarization degree of the photoluminescence is a direct measure of the net magnetization of CrPS$_{4}$. Complementary, Raman scattering measured as a function of magnetic field and temperature enables the determination of the magnetic susceptibility curve of the material. Our experimental results are backed by Our experimental results are supported by density functional theory calculations that take as input the lattice parameters determined from temperature-dependent X-ray diffraction measurements. This allows us to explain the impact of spin ordering on the spectral position of Raman transitions in CrPS$_4$, as well as anomalous temperature shifts of selected of them. The presented method for all-optical determination of the magnetic properties is highly promising for studies of spin ordering and magnetic phase transitions in single- or a few-layer samples of magnetic layered materials, for which a poor signal-to-noise ratio precludes any reliable neutron scattering or magnetometry measurements.

cond-mat.mtrl-sci↗

arXiv2024

Crystal anisotropy implications on the intrinsic magnetic and optical properties in van der Waals FePS3

Antiferromagnetic (AFM) FePS3 has gained significant interest recently for its potential applications in spin-related devices. A single layer is comprised of a honeycomb network, stabilized by long-range spin-exchange interactions, with a zigzag or Neel arrangement of the Fe-atoms. This study exposed, for the first time, a strong impact of lateral crystal distortion on the magnetic arrangement and optical properties of FePS3. This impact was deciphered by correlating photoluminescence (PL) observations with single-crystal XRD which uncovered anisotropy in the a/b crystallographic plane. Thus, induceing a breakage in the inversion symmetry in FePS3 causing changes in it's electronic and optical transitions. The MPL observations exhibited an unexpected band-edge circularly polarized recombination emission, while off-band-edge transitions were linearly polarized. Also, temperature-dependent MPL measurements reflected zigzag-AFM at low temperatures and the coexistence of zigzag or Neel at mid temperatures. Theoretical calculation implementing anisotropy in spin-exchange interactions among Fe atom's nearest neighbors revealed stabilized zigzag arrangement tilted away from the a-axis. Furthermore, DFT calculations of the electronic band-edge predicted split states in degenerate symmetric points (K+/K-) for zigzag structure and non-degenerate for the Neel arrangement. Highlighting the importance of the inclusion of a crystallographic anisotropy parameter for the simulation of the experimental observations.

cond-mat.mtrl-sci↗

arXiv2024

Tuning Magnetic and Optical Properties in MnxZn1-xPS3 Single Crystals by the Alloying Composition

The exploration of two-dimensional (2D) antiferromagnetic (AFM) materials has shown great promise and interest in tuning the magnetic and electronic properties as well as studying magneto-optical effects. The current work investigates the control of magneto-optical interactions in alloyed MnxZn1-xPS3 lamellar semiconductor single crystals, with the Mn/Zn ratio regulating the coupling strength. Magnetic susceptibility results show a retention of AFM order followed by a decrease in Néel temperatures down to ~ 40% Mn concentration, below which a paramagnetic behavior is observed. Absorption measurements reveal an increase in bandgap energy with higher Zn(II) concentration, and the presence of Mn(II) d-d transition below the absorption edge. DFT+U approach qualitatively explained the origin and the position of the experimentally observed mid band-gap states in pure MnPS3, and corresponding peaks visible in the alloyed systems MnxZn1-xPS3. Accordingly, emission at 1.3 eV in all alloyed compounds results from recombination from a 4T1g Mn(II) excited state to a hybrid p-d state at the valence band. Most significant, temperature-dependent photoluminescence (PL) intensity trends demonstrate strong magneto-optical coupling in compositions with x > 0.65. This study underscores the potential of tailored alloy compositions as a means to control magnetic and optical properties in 2D materials, paving the way for advances in spin-based technologies.

cond-mat.mtrl-sci↗

arXiv2024

Lattice-dynamics and in-plane antiferromagnetism in MnxZn1_xPS3 across the entire composition range

Alloyed MnxZn1_xPS3 samples have been grown covering the whole compositional range and studied by means of Raman spectroscopy at temperatures covering from 4K up to 850K. Our results, supported by SQUID magnetic measurements, allowed, from one hand, to complete the magnetic phase diagram of MnxZn1_xPS3 and establish x>0.3 as the composition at which the alloy retains antiferromagnetism and, from the other hand, to identify the Raman signatures indicative of a magnetic transition. The origin of these Raman signatures is discussed in terms of spin-phonon coupling resulting in the appearance of low- and high-frequency zone-folded phonon modes. For the alloy, an assignment of the 1st and 2nd order modes is provided with the aid of first-principle lattice-dynamical calculations. The compositional dependence of all phonon modes is described and the presence of zone-folded modes is shown to take place for both, the alloy and MnPS3. Finally, a comparison of the Raman spectra of ZnPS3 to other compounds of the transition-metal phosphorous trisulfide family allowed shows that low-frequency phonon peaks exhibit an abnormally large broadening. This is consistent with previous claims on the occurrence of a second-order Jahn-Teller effect that takes place for ZnPS3 and Zn-rich MnxZn1_xPS3.

cond-mat.mtrl-sci↗

arXiv2023

Electronic band structure changes across the antiferromagnetic phase transition of exfoliated MnPS$_3$ probed by $μ$-ARPES

Exfoliated magnetic 2D materials enable versatile tuning of magnetization, e.g., by gating or providing proximity-induced exchange interaction. However, their electronic band structure after exfoliation has not been probed, most likely due to their photochemical sensitivity. Here, we provide micron-scale angle-resolved photoelectron spectroscopy of the exfoliated intralayer antiferromagnet MnPS$_3$ above and below the Néel temperature down to one monolayer. The favorable comparison with density functional theory calculations enables to identify the orbital character of the observed bands. Consistently, we find pronounced changes across the Néel temperature for bands that consist of Mn 3d and 3p levels of adjacent S atoms. The deduced orbital mixture indicates that the superexchange is relevant for the magnetic interaction. There are only minor changes between monolayer and thicker films demonstrating the predominant 2D character of MnPS$_3$. The novel access is transferable to other MPX$_3$ materials (M: transition metal, P: phosphorus, X: chalcogenide) providing a multitude of antiferromagnetic arrangements.

cond-mat.mtrl-sci↗

arXiv2022

Spectroscopy and structural investigation of iron phosphorus trisulfide -- FePS$_3$

Lamellar structures of transition metal phosphorus trisulfides possess strong intralayer bonding, albeit adjacent layers are held by weak van der Waals interactions. Those compounds received enormous interest due to their unique combination of optical and long-range magnetic properties. Among them, iron phosphorus trisulfide (FePS$_3$) gathered special attention for being a semiconductor with an absorption edge in the near-infrared, as well as showing an Ising-like anti-ferromagnetism. We report a successful growth of centimeter size bulk FePS$_3$ crystals with a chemical yield above 70%, whose crystallographic structure and composition were carefully identified by advanced electron microscopy methodologies, including atomic resolution elemental mapping, along with photoelectron spectroscopy. The knowledge on the optical activity of FePS$_3$ is extended utilizing temperature-dependent absorption and photoacoustic spectroscopies, while measurements were corroborated with density-functional theory calculations. Temperature-dependent experiments showed a small and monotonic band-edge energy shift down to 115 K and exposed the interconnected importance of electron-phonon coupling. Most of all, the correlation between the optical behavior and the magnetic phase transition is revealed, which shows the practical utilization of temperature-dependent optical absorption to investigate magnetic interactions.

cond-mat.mtrl-sci↗