Gallium Telluride (GaTe) has garnered significant attention for its unique optical properties, yet its potential for optical spin polarization driven by triplet excitonic states analogous to those in GaSe remains largely unexplored. In this study, we investigate the optical spin polarization in GaTe through circularly polarized photoluminescence (CPPL) measurements at both room and cryogenic temperatures. Notably, a typical GaTe flake exhibited a robust degree of circular polarization (DoCP) of approximately 70% at 77 K under 633 nm laser excitation. The DoCP was found to depend strongly on flake thickness, showing no clear trend for flakes thinner than 25 nm, while flakes thicker than 25 nm exhibited a pronounced decrease in DoCP, attributed to the increasing exciton photoluminescence (PL) decay lifetime z0 relative to the spin relaxation time zs. The DoCP also varied significantly with excitation wavelength: for a 163 nm thick flake, the DoCP was 25% under 633 nm excitation but dropped to 5% when excited at 532 nm. Temperature dependence studies further revealed a nonmonotonic behavior of the DoCP, linked to the interplay between exciton PL decay lifetime z0 and spin relaxation time zs. These findings highlight the complex spin dynamics in GaTe and its potential applications in spintronic devices.

We present a comprehensive investigation of the effects of Fe doping on the lattice dynamics, magnetic ordering, and magneto-transport properties of the intercalated van der Waals antiferromagnets Co1-xFexNb3S6 (x = 0.1 and 0.3). Temperature- and polarization-dependent Raman scattering measurements reveal a pronounced blue shift of the 180 cm-1 phonon mode with increasing Fe concentration, indicating enhanced sensitivity of lattice vibrations to Fe-induced structural and mass effects. While the temperature evolution of the phonon modes is dominated by conventional anharmonic phonon softening, subtle anomalies observed near the Néel temperature for x = 0.1 point to weak spin-phonon coupling. Electrical transport and magnetic susceptibility data show clear signatures of the antiferromagnetic phase transitions at TN 20.5-23.7 K for x = 0.1 and TN 32.0 K for x = 0.3. Out-of-plane magnetization measurements reveal hysteretic behavior with two field-induced transitions for x =0.1, which evolve into a single hysteresis loop at x =0.3, signaling a subtle reconstruction of the magnetic ground state. Magneto-transport measurements for x = 0.1 further display a butterfly-shaped hysteretic magnetoresistance and a weak topological Hall effect; however, both features are strongly suppressed at x = 0.3. These results illustrate the critical role of Fe-induced magnetic structure reconstruction in fine-tuning topological and magnetic transport phenomena in intercalated van der Waals antiferromagnets.

Two-dimensional semiconducting materials have a wide range of applications in various fields due to their excellent properties and rich physics. Here, we report a detailed investigation of temperature-dependent Raman and photoluminescence measurements on vertically aligned 2H-SnS2 grown by the CVD method. Our results established the tunability of resonant Raman scattering with varying temperature, i.e., a crossover between resonance and non-resonance conditions for the current system. We also discussed the temperature as well as laser power dependence of the low-frequency asymmetric Raman mode, which is the interlayer shear mode. The temperature dependence of the intensity of the phonon modes also manifests the tunability of the resonant Raman scattering with temperature. Our temperature-dependent photoluminescence measurement shows the strong temperature dependence of the excitonic peaks and this is confirmed by the laser power dependence of the photoluminescence measurement at room temperature. Our investigation may help to design and fabricate devices based on vertically aligned 2H-SnS2 and other similar materials in the future.

The spin-entangled Zhang-Rice (ZR) exciton observed in the van der Waals magnet NiPS3 has garnered significant interest due to its strong correlation with magnetic ordering and long coherence. Herein, we present a temperature- and polarization-dependent photoluminescence (PL) study of anion-substituted NiPS3-xSex (x = 0.008, 0.03, 0.06, and 0.09) to explore the nature and dynamics of the ZR exciton. Our results reveal that even a small percentage of anion substitution effectively destroys and modulates the ZR exciton, as evidenced by the emergence of a weaker, lower-energy PL peak in addition to the primary ZR peak. Both peaks share the same anisotropic polarization but differ in their peak energy shift and intensity evolution with Se substitution, suggesting varying charge transfers of p-orbitals. Notably, the ZR exciton undergoes thermal destabilization at much lower temperatures than two-magnon excitations, highlighting that p-orbital inhomogeneity beyond the magnetic ordering structure is a decisive factor in driving its thermal quenching.

Quasi-elastic scattering (QES) serves as a sensitive probe of slow spin fluctuations in low-dimensional magnetic systems, multiferroics, and frustrated quantum magnets. Here, we investigate spin and lattice dynamics in anion-substituted NiPS3-xSex using temperature- and polarization-dependent Raman spectroscopy. Above the N & eacute;el temperature, the Raman spectra in the cocircular polarization configuration show a QES response near zero frequency, which is described by a Lorentzian profile. This QES is linked to paramagnetic spin fluctuations and the associated energy density of spins, which are slightly suppressed with increasing Se content. Notably, even inside the magnetically ordered state (below 50 K), we observe a strong enhancement of this QES signal, indicative of persistent fluctuations of the ordered magnetic moments. Concurrently, spin-phonon coupling manifests as an anomalous renormalization of phonon self-energy in certain phonon modes that couple strongly to the magnetic ions, with their frequencies shifting systematically as Se concentration increases. These results suggest that spin fluctuations and lattice vibrations remain strongly intertwined in NiPS3-xSex, and that chemical substitution provides a means to tune this spin-phonon coupling in van der Waals magnets.

Trilayer nickelates are a rich class of materials exhibiting diverse correlated phenomena, including superconductivity, density wave transitions, non-Fermi liquid behavior along with an unusual metal-to-metal transition around T* similar to 150 K. Understanding the electronic correlations as well as lattice and charge dynamics is crucial to unravel the origin of superconductivity and other instabilities in nickelates. Our in-depth Raman measurements show that trilayer nickelate, La4Ni3O10, shows transition from electron-phonon coupled phase to the electron-electron correlated one below charge density wave transition around T* with an estimated energy gap ( Delta) of similar to 18-20 meV. The transition around T* is also accompanied by the emergence of zone-folded phonon modes reflecting the transition into a charge density wave phase. Phonon modes self-energy parameters show anomalous changes around T* attributed to the electron-electron correlations, and the renormalization rate of the phonon is much slower in the charge-ordered phase compared to the phase above T*. The transition around T* is marked by a suppression of the electron-phonon coupling parameter by similar to 70%, a change in the quasiparticle dynamics from non-Fermi liquid to the Landau-Fermi liquid-type behavior estimated using the low-frequency ( omega -> 0) Raman response.

Two-dimensional magnetic materials with tunable physical parameters are emerging as potential candidates for topological phenomena as well as applications in spintronics. The famous Mermin-Wagner theorem states that spontaneous spin symmetry cannot be broken at finite temperature in low dimensional magnetic systems which forbids the possibility of a transition to a long-range ordered state in a two-dimensional magnetic system at finite temperature. Though, there are some exceptions to Mermin-Wagner theorem in particular low dimensional magnetic systems with topologically ordered phase transitions. Here, we present an in-depth temperature dependent analysis for the bulk single crystals of two-dimensional (Mn1−xNix)2P2S6 with x = 1, 0.7, 0.3, 0 using the Raman spectroscopy supported by first-principles calculations of the phonon frequencies. We observed multiple phase transitions with tunability as a function of doping associated with the short and long-range spin-spin correlations. First transition at ~ 150 K to ~ 170 K for x = 0 to x = 0.7, and second one from ~ 60 K to ~ 153 K. Quite interestingly, a third transition is observed at low temperature (much below their respective TN) ~ 24 K to ~ 60 K and is attributed to the potential topological phase transition. These transitions are marked by the distinct changes observed in the temperature evolution of the phonon self-energy parameters, modes intensity and dynamic Raman susceptibility.

To manufacture complex parts using abrasive waterjets (AWJs) in milling mode, one should ensure that the local features of the target part geometry match with the channel shape produced by manipulating the operating parameters, such as jet impingement angle (alpha) and traverse speed (V-f). Hence, generating surfaces with tight tolerances demands control over the channel cross-section profile (CP) and its characteristics (maximum erosion depth, top width, cross-section area, and trailing edge angle). Despite AWJ technology's existence for decades, there have been limited attempts to obtain control over channel geometries. Since AWJ is a complex three-phase mixture (air-water-particles), determining the particle flow properties in AWJ for material removal is of utmost importance. These circumstances seek to establish a modelling approach for predicting the channel geometry under the change in alpha and V-f. This paper proposes an innovative model for predicting CPs obtained at shallow-angle jet (SAJ) impinged erosion trials, incorporating the insights gained on channel formation mathematically. The Ti-6Al-4V alloy is highly challenging to mill by conventional methods used for experiments. The modelling results demonstrate that by considering the mathematical relationship between the specific cutting energy associated with alpha and V-f and corresponding jet flow properties in the model, the prediction capability improved by 98 %. Overall, within the range of alpha (50(0)-90(0)) and V-f (3000-5000 mm/min), the model's prediction error of channel characteristics is <10 %, and the mean absolute error in channel shape is 22.74 mu m. Strong conformity is observed with a correlation coefficient of 0.98 between modelled and experimental profiles.

Two-dimensional cobalt-based honeycomb oxide Na2Co2TeO6 is an important candidate for the realization of Kitaev physics and may provide future platform for the quantum computation and quantum technology. Here, we report an in-depth temperature as well as polarization dependent inelastic light scattering (Raman) measurements on the single crystals of quasi-two-dimensional Na2Co2TeO6. Our study reveal signature of multiple phase transitions i.e. long-range zigzag antiferromagnetic transition (TN) at 30 K, ferroelectric transition (TFE) at 70 K, and a crossover from pure paramagnetic phase to a quantum paramagnetic phase around 150 K reflected in the renormalized self-energy parameters of the Raman active phonon modes. A distinct signature of spin reorientation deep into the AFM phase around TSR 17 K is observed, marked by the clear change in the frequency and linewidth slopes. We also observed an asymmetric phonon mode in the low frequency region, and it appears below the transition temperature 50 K, attributed to the magnetic excitations other than the magnon. The Raman signature of multiple crystal-field excitations at low temperature along with lifting of the Kramers degeneracy is also observed. Signature of the underlying broad magnetic continuum in the quantum paramagnetic phase and its temperature dependence suggest presence of frustrated magnetic interaction in the quantum paramagnetic phase below 150 K.

In recent years, group six of the atomically thin two-dimensional transition metal dichalcogenides (VI-TMDCs) like MX2 (M = Mo, W and X = S, Se), have gain a tremendous attention due to their unique electronic and optoelectronic properties, strong spin-orbit coupling, spin and valley degrees of freedom, thickness dependent modulation of the electronic and vibrational properties and the existence of a zoo of excitonic quasiparticle energy states like excitons, trions and bi-excitons. The understanding of these various aspects has become pertinent from the fundamental research as well as potential applications point of view. Raman spectroscopy has been established to be a very effective, powerful, sensitive and non-destructive technique to understand the various aspects of group VI-TMDCs. Furthermore, Resonant Raman spectroscopy, a special form of Raman spectroscopy, has played a vital role in our current understanding of group VI-TMDCs and lead to the observation of conventionally/generally forbidden backscattering/infrared active phonons as well as the phonons from the entire Brillouin zone, Davydov splitting, electron (exciton)-phonon coupling etc. The observation of these various aspects is not possible with the normal Raman/non-resonant Raman spectroscopy. Moreover, due to the existence of various excitonic quasiparticles energy states in these materials provide a better platform to understand the crossover between resonant and non-resonant conditions with different external perturbations such as laser excitation energy, thickness of the sample, temperature, pressure, strain etc. In this chapter we will discuss these various aspects of resonant and non-resonant Raman scattering and their remarkable uses to understand the various intriguing properties of group VI-TMDCs.

The spin-1 triangular lattice Heisenberg antiferromagnet Ca3NiNb2O9 3 NiNb 2 O 9 and its sister compounds are conjectured to promote the formation of many-body quantum entangled states such as a quantum spin liquid (QSL), an exotic phase which features fractionalized quasiparticle excitations and emergent gauges. We probe the single crystal of Ca3NiNb2O9 3 NiNb 2 O 9 using an in-depth Raman spectroscopic technique. Our measurements provide evidence for the fractionalized excitations, suggesting that the current system is in close proximity to the QSL phase. This is also in line with the proposed higher-order fractional magnetization plateau in this system, as these plateaus have an intricate relationship with the spin entanglement. We observed unconventional underlying scattering as a broad continuum with an intensity that shows fermionic statistics. Additionally, phonon modes show Fano asymmetry, also conjectured as a fingerprint of the spin-liquid phase, and above a critical Raman shift also show fermionic statistics in their intensity evolution.

The intricate interplay between spin and lattice degrees of freedom in two-dimensional magnetic materials plays a pivotal role in modifying their magnetic characteristics, engendering hybrid quasiparticles, and implementing functional devices. Herein, we present our comprehensive and in-depth investigations on magnetic and lattice excitations of MnPSe3-xSx 3 - x S x (x x = 0, 0.63, and 1.68) alloys, utilizing temperature- and polarization- dependent Raman scattering. Our experimental results reveal the occurrence of multiple phase transitions, evidenced by notable changes in phonon self-energy and the appearance or splitting of phonon modes. These emergent phases are tied to the development of long and short-range spin-spin correlations, as well as to spin reorientations or magnetic instabilities. Our analysis of two-magnon excitations as a function of temperature and composition showcases their hybridization with phonons whose degree weakens with increasing x . Moreover, the suppression of spin-dependent phonon intensity in chemically most-disordered MnPSe3-xSx 3 - x S x (x x = 1.68) . 68) suggests that chalcogen substitution offers a control knob of tuning spin and phonon dynamics by modulating concurrently superexchange pathways and a degree of trigonal distortions.

Mermin-Wagner theorem forbid spontaneous symmetry breaking of spins in one/two-dimensional systems at finite temperature and rules out the stabilization of this ordered state. However, it does not apply to all types of phase transitions in low dimensions such as topologically ordered phase rigorously shown by Berezinskii-Kosterlitz-Thouless (BKT) and experimentally realized in very limited systems such as superfluids, superconducting thin films. Quasi 2D van der Waals magnets provide an ideal platform to investigate the fundamentals of low-dimensional magnetism. We explored the 2D honeycomb antiferromagnetic single crystals of (NixFe1-x)2P2S6 with varying spins ( ) using in depth temperature dependent Raman measurements supported by first-principles calculations of the phonon frequencies. As a function of doping, a tunable transition from paramagnetic to antiferromagnetic ordering is shown via phonons reflected in the strong renormalization of the self-energy parameters of the Raman active phonon modes. An anomalously broad magnetic continuum attributed to two-magnon excitations is observed and its coupling with the phonons is revealed in the observation a Fano line asymmetry. Interestingly, the two-magnon continuum is observed only for the finite doping understood invoking underlying nature of insulator these materials belongs to, i.e. exchange interaction between transition metals via surrounding ligands (sulphur) and the resonance involving phonon modes associated with the (P2S6) cage. Quite surprisingly, we also observed renormalization of the phonon modes much below the long-range magnetic ordered temperature attributed to the topological ordered state, namely the BKT phase, which is also found to change as a function of doping. The extracted critical exponent of the order-parameter evince the signature of topologically active state driven by vortex-antivortex excitations.

Phase transitions with lowering temperature is a manifestation of decreased entropy and within the Landau theoretical framework these are accompanied by the symmetry breaking. Whenever a symmetry is broken weakly or strongly, it leaves its trail and the same may be captured indirectly using renormalization of the quasi-particle excitations. Cr2Ge2Te6, a quasi-two-dimensional magnetic material, provides a rich playground to probe dynamics of the quasi-particle excitations as well as multiple phase transitions with lowering temperature intimately linked with the lattice and spin degrees of freedom. Here, we report in-depth inelastic light scattering measurements on single crystals of Cr2Ge2Te6 as a function of temperature, from 6 K to 330 K, and polarization. Our measurements reveal the long as well as short range ordering of the spins below Tc (~ 60 K) and T* (~ 180 K), respectively; setting the stage for broken rotational and time reversal symmetry, gauged via the distinct renormalization of the phonon self-energy parameters along with the modes intensity. Our measurements also uncovered an intriguing dependence of the interaction strength between discrete state (phonon here) and the underlying continuum, quantified using the Fano asymmetry parameter, as a function of the scattered light polarization. Our results suggest the possibility of tuning the interaction strength using controlled scattered light and symmetry in this 2D magnet.

The intricate interplay between spin and lattice degrees of freedom in two-dimensional magnetic materials plays a pivotal role in modifying their magnetic characteristics, engendering hybrid quasiparticles, and implementing functional devices. Herein, we present our comprehensive and in-depth investigations on magnetic and lattice excitations of MnPSe3-xSx (x = 0, 0.5, and 1.5) alloys, utilizing temperature- and polarization-dependent Raman scattering. Our experimental results reveal the occurrence of multiple phase transitions, evidenced by notable changes in phonon self-energy and the appearance or splitting of phonon modes. These emergent phases are tied to the development of long and short-range spin-spin correlations, as well as to spin reorientations or magnetic instabilities. Our analysis of two-magnon excitations as a function of temperature and composition showcases their hybridization with phonons whose degree weakens with increasing x. Moreover, the suppression of spin-dependent phonon intensity in chemically most-disordered MnPSe3-xSx (x = 1.5) suggests that chalcogen substitution offers a control knob of tuning spin and phonon dynamics by modulating concurrently superexchange pathways and a degree of trigonal distortions.

Titanium alloys are used in engineering applications due to their high strength-to weight ratio. However, it is challenging to manufacture parts from it. On the other hand, abrasive waterjet (AWJ) has demonstrated its capabilities in milling parts in titanium alloys. However, AWJ milling technology is still nascent due to a lack of accurate control over material removal. The material removal rate (MRR) is one measure that decides productivity. Towards contributing to the acceptance of the AWJ milling technology, a model for accurate prediction of the MRR is proposed in this work. Hence, a suitable generic geometry that accurately mimics the material removal under various AWJ conditions is identified. By integrating the identified geometry (rectangle, trapezium, triangle) with the maximum erosion depth and the top kerf width, the MRR is predicted. Results show that the estimated MRR using a triangular kerf CP area correlate well with the experimental MRR.