Orientation Of Crystal Axes Research Articles

Thin film lithium niobate electro-optic modulator with reduced half-wave voltage length product through design

This paper aims at shortening electrode spacing in a thin film lithium niobate (TFLN) electro-optic modulator (EOM) while avoiding an increase in metal absorption loss, thereby reducing the half-wave voltage length product (V π ⋅L). Through numerical simulations, we find that metal absorption loss reaches its peak values when the optical modes of the metal-clad dielectric waveguide and ridged waveguide hybridize. This negative effect can be mitigated by adjusting the electrode width to modify the optical mode of the metal-clad dielectric waveguide. In addition, we raise the vertical position of the electrodes to further mitigate metal absorption loss and reduce the electrode spacing. By calculating the optimal buffer layer thickness for two crystal axis orientations, our findings reveal a 19% reduction in V π ⋅L at conventional crystal axis orientation (θ=±90∘) and a 16% decrease at unconventional crystal axis orientation (θ=54∘). Notably, V π ⋅L at unconventional crystal axis orientation is 5% lower than at conventional crystal axis orientation. These findings demonstrate the effectiveness of geometric configuration optimization toward enhancing the efficiency and performance of the TFLN EOM.

Spatial orientation of CdS nanowiresbased on second harmonic generation spectroscopy and microscopic Imaging

The second harmonic generation (SHG), as a nonlinear optical effect, has a wide range of applications in obtaining information such as material composition, structure, and properties due to its good polarization sensitivity. Although SHG spectroscopy or SHG microscopy has been used to explore the precise positioning or tracking of nanowires, there are few reports on the combination of SHG spectroscopy and SHG microscopy to study the structure of nanomaterials and the spatial orientation of crystal axes. In this work, we investigate the spatial orientation and crystal axis orientation of cadmium sulfide (CdS) nanowires by combining SHG spectroscopy and microscopic imaging. Firstly, we experimentally and theoretically study the spectral intensity of the SHG of CdS nanowires with the polarization direction of the incident light based on the all-optical analysis method proposed by the predecessors. We also analyze the influence of the azimuth angle of the crystal axis γ, ω and φ on the pattern of the SHG of CdS nanowires in detail. Secondly, through the mutual verification of theoretical calculations and experimental measurement results, we successfully determine the three axial orientations of a single CdS nanowire. Finally, we also investigate the spatial orientation of a single CdS nanowire by using the polarization-dependent SHG microscopic imaging method. It is shown that different parts of the CdS nanowire have different SHG responses when the polarization is changed. These results provide a new idea and an important reference for studying the application of SHG spectroscopy and microscopic imaging in the research of high-precision spatial positioning of nanomaterials. This study provides important enlightenment for realizing the potential applications of nanomaterials in biomedicine.

Polarization superposition of room-temperature polariton condensation

A methodology for forming a qubit state is essential for quantum applications of room temperature polaritons. While polarization degree of freedom is expected as a possible means for this purpose, the coupling of linearly polarized polariton condensed states has been still a challenging issue. In this study, we show a polarization superposition of a polariton condensed states in an all-inorganic perovskite microcavity at room temperature. We achieved the energy resonance of the two orthogonally polarized polariton modes with the same number of antinodes by exploiting the blue shift of the polariton condensed state. The polarization coupling between the condensed states results in a polarization switching in the polariton lasing emission. The orthorhombic crystal structure of the perovskite active layer and/or a slight off-axis orientation of the perovskite crystal axis from the normal direction of microcavity plane enables the interaction between the two orthogonally polarized states. These observations suggest the use of polariton polarization states as a promising room temperature quantum technology.

Review: Structural, elastic, and thermodynamic properties of cubic and hexagonal ScxAl1−xN crystals

A review of the structural, elastic, and thermodynamic properties of cubic and hexagonal ScxAl1−xN crystals over the range of possible random alloys is provided. Based on measured and simulated lattice and internal cell parameters of NaCl (B1), CsCl (B2), and α-ZnS (B3) type cubic ScxAl1−xN lattices as well as of β-ZnS (B4), lh-MgO (Bk), and NiAs (B81) type hexagonal ScxAl1−xN crystals, their atomic positions, distances to nearest neighbor atoms, geometric dimensions of crystal cells, mass density, as well as their average bond length and bond angles are presented in dependence on the alloy composition. The understanding gained about the crystal lattices is used to provide a model for the transitions from the β-ZnS to the lh-MgO or NaCl lattice induced by the alloying of AlN with ScN. Based on published data sets of stiffness coefficients, the compliance coefficients, Young's modulus, shear modulus, Poisson's ratio, compressibility, and the sound velocities are presented in relation to the orientation of representative crystal planes and axes for rock salt, layered hexagonal, and wurtzite ScxAl1−xN crystals. Particular attention is paid to the directional anisotropies of elastic properties of the different crystal lattices if Sc atoms substitute an increasing number of Al atoms. Based on sound velocities determined, an overview of the fundamental thermodynamic properties of cubic and hexagonal ScxAl1−xN alloys is provided, such as the Debye temperature, heat capacity, minimum heat conduction, and melting temperature.

Hall Effect Anisotropy in the Paramagnetic Phase of Ho0.8Lu0.2B12 Induced by Dynamic Charge Stripes.

A detailed study of charge transport in the paramagnetic phase of the cage-cluster dodecaboride Ho0.8Lu0.2B12 with an instability both of the fcc lattice (cooperative Jahn-Teller effect) and the electronic structure (dynamic charge stripes) was carried out at temperatures 1.9-300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals of Ho0.8Lu0.2B12 samples with different crystal axis orientation were investigated in order to establish the singularities of Hall effect, which develop due to (i) the electronic phase separation (stripes) and (ii) formation of the disordered cage-glass state below T*~60 K. It was demonstrated that a considerable intrinsic anisotropic positive component ρanxy appears at low temperatures in addition to the ordinary negative Hall resistivity contribution in magnetic fields above 40 kOe applied along the [001] and [110] axes. A relation between anomalous components of the resistivity tensor ρanxy~ρanxx1.7 was found for H||[001] below T*~60 K, and a power law ρanxy~ρanxx0.83 for the orientation H||[110] at temperatures T < TS~15 K. It is argued that below characteristic temperature TS~15 K the anomalous odd ρanxy(T) and even ρanxx(T) parts of the resistivity tensor may be interpreted in terms of formation of long chains in the filamentary structure of fluctuating charges (stripes). We assume that these ρanxy(H||[001]) and ρanxy(H||[110]) components represent the intrinsic (Berry phase contribution) and extrinsic (skew scattering) mechanism, respectively. Apart from them, an additional ferromagnetic contribution to both isotropic and anisotropic components in the Hall signal was registered and attributed to the effect of magnetic polarization of 5d states (ferromagnetic nano-domains) in the conduction band of Ho0.8Lu0.2B12.

A Tolerance‐Enhanced Spontaneous Parametric Downconversion Source of Bright Entangled Photons

AbstractSpontaneous parametric down‐conversion (SPDC), a primary resource of photonic quantum entangled states, strongly depends on the intrinsic phase matching condition. This makes it susceptible to changes in factors such as the pump wavelength, crystal temperature, and crystal axes orientation. Such intolerance to changing environmental factors prohibits deployment of SPDC‐based sources in non‐ideal environments outside controlled laboratories. Here, a novel system architecture based on a hybrid linear and non‐linear solution that is shown to make the source tolerance‐enhanced without sacrificing brightness. This linear solution is a lens‐axicon pair, judiciously placed, which is tested together with two common non‐linear crystals, quasi‐phase‐matched periodically‐poled KTiOPO4, and birefringent‐phase‐matched BiB3O6. This approach has the benefit of simultaneous tolerance to the environment and high brightness, which is demonstrated by using the proposed architecture as a stable entangled photon source and a spectral brightness as high as 22.58 ± 0.15 kHz mW−1 with a state fidelity of 0.95 , yet requiring a crystal temperature stability of only ±0.8 °C, a 5 × enhanced tolerance as compared to the conventional high brightness SPDC configurations is reported. This solution offers a new approach to deployable high‐brightness quantum sources that are robust to their environment, for instance, in satellite‐based quantum applications.

Influence of alloying and structural transition on the directional elastic and isotropic thermodynamic properties of wurtzite and layered hexagonal ScxAl1−xN crystals

The structural, elastic, and basic thermodynamic properties of hexagonal ScxAl1−xN crystals are calculated and discussed over the whole range of possible random alloys, including the transition from wurtzite to the layered hexagonal structure. Based on a review of lattice and internal parameters in combination with complete datasets of stiffness coefficients published in the literature, differing in the considered alloying intervals and the predicted structural transitions, changes in the crystal lattices caused by the substitution of aluminum by scandium atoms are discussed and illustrated. Crystal properties like the mass densities, average bond angles, and bond lengths are calculated, and the compliance coefficients, Young's modulus, shear modulus, Poisson's ratio, compressibility, and sound velocities are determined depending on the alloy composition and in relation to the orientation of crystal planes and axes. Particular attention is paid to the occurring directional anisotropies and the changes in structural and elastic properties in the alloy region of the structural transition between wurtzite and layered hexagonal ScxAl1−xN crystals. The acoustic velocities determined are used to calculate basic thermodynamic properties such as the Debye temperature, heat capacity, and minimum heat conduction, as well as to evaluate both the influence of the alloying and the structural transition on these properties.

Field-Tuning Mechanisms of Spin Switching and Spin Reorientation Transition in Praseodymium-Erbium Orthoferrite Single Crystals.

Field-tuning mechanisms of spin switching and spin reorientation (SR) transition were investigated in a series of high-quality single crystal samples of PrxEr1-xFeO3 (x = 0, 0.1, 0.3, 0.5) prepared using the optical floating zone method. The single crystal quality, structure, and axis orientation were determined by room-temperature powder X-ray diffraction, back-reflection Laue X-ray diffraction, and Raman scattering at room temperature. Magnetic measurements indicate that the type and temperature region of SR transition are tuned by introducing different ratios of Pr3+ doping (x = 0, 0.1, 0.3, 0.5). The trigger temperatures of spin switching and magnetization compensation temperature of PrxEr1-xFeO3 crystals can be adjusted by doping with different proportions of Pr3+. Furthermore, the trigger temperature of the two types of spin switching in Pr0.3Er0.7FeO3 along the a-axis can be regulated by an external field. Meanwhile, the isothermal magnetic field-triggered spin switching effect is also observed along the a and c-axes of Pr0.3Er0.7FeO3. An in-depth understanding of the magnetic coupling and competition between the R3+ and Fe3+ magnetic sublattices, within the RFeO3 system, has important implications for advancing the practical applications of the relevant spin switching materials.

Study of a bi-axial (KTP) crystal using double Stokes–Mueller polarimetry

In this paper, we report the significance of the double Stokes–Mueller polarimetry (DSMP) technique, to characterize a large size ([Formula: see text][Formula: see text]mm) Potassium titanyl phosphate (KTP) crystal. The crystal undergoes second harmonic generation with type II phase matching. The study of standard KTP crystal using the DSMP technique helps to validate the efficiency of this technique. We were able to extract the crystal’s double Mueller matrix, relative contribution of the susceptibility tensor components, the phase difference between the susceptibility tensor components, etc. We could determine the crystal axes orientation using this optical technique, which was not possible through a single crystal X-Ray diffraction technique for such a large size crystal for which both optic axes and crystallographic axes are the same. Axes direction determined from polarization microscope measurements and Laue diffraction measurements on KTP crystal is compared with those obtained from DSMP measurements.

Use of 4×4 transfer matrix method in the study of surface magnon polaritons via simulated attenuated total reflection measurements on the antiferromagnetic semiconductor MnF2

The surface magnon polaritons (SMPs) present in thin film antiferromagnet semiconductors can be extremely confined, having most of their energy distributed within the magnetic medium. For extremely thin films these SMPs can therefore be well described using a quasimagnetostatic treatment. In this work Berreman's $4\ifmmode\times\else\texttimes\fi{}4$ transfer matrix method (TMM) is used to study the SMPs supported by thicker films, beyond the magnetostatic approximation. Focus is placed on the antiferromagnet semiconductor ${\mathrm{MnF}}_{2}$ for which attenuated total reflection measurements are modeled, probing the hyperbolic dispersion of the medium. The dispersion relations from both the TMM and the analytical quasimagnetostatic approximation are compared. For thicker films, the coupling efficiencies into the SMP energy channels are analyzed as a function of air gap distances. The TMM is used to probe the SMP dispersion for realistic experimental configurations with modifications including type of substrate, film thickness, and crystal axis orientation. Rich phenomena are observed such as strong SMP-waveguide mode coupling and SMPs with negative refraction.

Thermopower and thermophase in a d -wave superconductor

In an unconventional superconductor, the interplay of scattering off impurities and Andreev processes may lead to different scattering times for electronlike and holelike quasiparticles. Such electron-hole asymmetry appears when the impurity scattering phase shift is intermediate between the Born and unitary limits and leads to an expectation for large thermoelectric effects. Here, we examine the thermoelectric response of a $d$-wave superconductor connected to normal-metal reservoirs under a temperature bias using a fully self-consistent quasiclassical theory. The thermoelectrically induced quasiparticle current is cancelled by superflow in an open circuit setup, but at the cost of a charge imbalance induced at the contacts and extending across the structure. We investigate the resulting thermopower and thermophase and their dependencies on scattering phase shift, mean free path, and interface transparency. For crystal-axis orientations such that surface-bound zero-energy Andreev states are formed, the thermoelectric effect is reduced as a result of locally reduced electron-hole asymmetry. For a semiballistic superconductor with good contacts, we find thermopowers of order several ${\mu}V/K$, suggesting a thermovoltage measurement as a promising path to investigate thermoelectricity in unconventional superconductors.

An experimental XAS and ab initio approach to describe the electronic and local structure of sodium nitroprussiate single crystals

The electronic and local structural properties of single crystals in the ground state (GS) of the photo-switchable compound Na2[Fe(CN)5NO]•2H2O (sodium nitroprussiate, SNP) have been investigated by X-ray Absorption Fine Structure Spectroscopy (XAFS) and FEFF simulations. In SNP, the XANES (X-ray Absorption Near Edge Structure) pre-edge region presents three distinct peaks with different intensities depending on the crystal axis orientation with respect to the polarization direction of the X-ray beam. The peaks correspond to a combination of 1s to 4p and 1s to 3d transitions with possibly mixed dipole and quadrupole character. The EXAFS fitting reveals, as expected, a biased structure according to the relative position of the crystal with respect to the beam polarization and the fittings are in accordance to theoretical values. The best fitted model has a large contribution from multi-scattering paths, which clarifies the interpretation of the actual peak contributions on the Fourier Transformed signal.

The application and associated problems of EBSD technique in fabric analysis

在过去的二十年里，EBSD（Electron Backscattered Diffraction），即电子背散射衍射测试技术，已广泛应用于韧性组构分析，成为变形运动学、流变学分析的常规手段。该方法主要应用于流变条件下矿物晶轴组构定向性分析，以判定流变剪切指向、对比应变强度、估算变形温度。理论上讲，EBSD法适用于所有矿物的全部晶轴定向的分析测试。然而鉴于天然变形的复杂性，笔者建议EBSD分析应以石英，特别是经历了动态重结晶的石英条带为组构分析的主要对象。长期以来，石英晶轴组构的不对称性被视作独立的剪切指向标志。然而，近年来基于天然变形和一般剪切实验的研究结果表明，塑性流变的剪切指向含义应为多重流变剪切指向标志综合判别比对的结果。尽管在提出之初，石英的轴组构开角被视作独立可靠的变形温度计（Kruhl，1998）。然而限于天然变形的复杂性，特别是对变质与变形阶段的对应、耦合的认识；尽管石英变形滑移系及石英晶轴组构开角可为动力变质温度提供重要的参考，但是石英晶轴组构开角并非独立的变形温度计。;In the last two decades, EBSD (Electron Backscattered Diffraction) has been widely used as a routine approach in ductile fabric analyses, focusing on flow kinematics and rheology of ductile deformation. It is predominantly applied to determining the shear-sense of the bulk flow, evaluating strain strength, and assessing deformation temperature via analyzing Crystallographic Preferred Orientation (CPO) and deformation mechanisms of recrystallized minerals. Theoretically, EBDS retains the potential to recover the crystal-axis orientation of all minerals. However, dynamically recrystallized quartz grains, particularly, quartz ribbons are recommended for EBDS analysis due to the complexities of natural deformation. Conventionally, quartz c-axis obliquity is used as a reliable and independent shear-sense indicator, while the c-axis opening angle and recrystallization mechanisms of quartz (i.e., bulging, subgrain rotation, and grain boundary migration) have been treated as deformation thermometers. However, recent studies on naturally deformed rocks and general-shear experiments indicate that cautions must be exercised when using EBSD results to extract flow kinematics and multi-criteria are suggested for a proper interpretation of flow kinematics in ductile shear zones. Similarly, limited to our understanding of the process of natural deformation, particularly the coupling between metamorphism and ductile deformation, crystal fabric-based deformation thermometers have their own caveats and limitations that EBSD-derived thermal data, the quartz c-axis opening-angles, may also be subject to multiple interpretations although it was originally proposed as an independent deformation thermometer (Kruhl, 1998).

Investigation for the Thermodynamic Polarization Degradation of the BaTiO3 Crystal Thin Films

According to the latest development of memory, it is found that the motion of ferroelectric domain wall is very important for the high-density non-volatile devices of ferroelectric materials. This paper mainly studies the microstructure of barium titanate (BaTiO3) crystal films with the molecular dynamics of crystal domain motion and then models the polarization degradation with the conservation of the nucleation energy-focusing and free energy thermodynamic processes in the crystalline domains. First, by the means of XRD diffractometer and JADE software, the crystal axis orientation of BaTiO3 thin film is analysed, and then the crystal axis orientation is determined by referring the published measurement results. Further, for the ferroelectric crystal BaTiO3 thin film, the thermodynamic process is studied and the temperature dependences of the polarization ratio with respect to the spontaneous polarization is modelled. Numerical simulations have shown the much higher temperature dependence on the nucleation energy than on the free energy in a domain wall system, leading to the possibility to reach a high polarization ratio with the optimal deposition conditions to control the local energy and the nucleation energy cost of crystalline domains.

Optically detected vibrations of crystal pendulum due to sun radiation

The optical experiments with suspended quartz crystals reflecting Laser-Doppler-Vibrometer (LDV) beam reveal an effect of crystal pendulum vibrations initiated by Sun's radiation of heavy particles. The LDV measures speed S(t) of oscillating crystal surface. The Fourier-transform of S(t) returns a spectrum of the acoustic vibrations with a few hertz frequency. The S(t) is a sine-type curve with amplitude depending on the time and space orientation of crystal axes. Maximum vibrational speed and corresponding crystal displacement from a position of equilibrium are observed when quartz piezoelectric axis is aimed toward the Sun. Experimental evidences exclude involvement of any electro-magnetic wave. The theoretical calculations for an oscillator driven by a periodic pulse-force are compared to the experimentally detected oscillations. The computations give a work done by an external force to move the crystal from its equilibrium to maximum displacement. It yields a mass of a thinkable particle that is necessary to initiate and support observed vibrations. In the case of individual particles propagating with a solar wind speed and hitting crystal, particle mass is of the order of 10 i×-21 kg. The physics of crystal-particle interaction may be related to gravitational pull of quartz atoms/ions and particle quantum properties such as matter waves.

Polarization-dependent nonlinear optical response in GeSe<sub>2</sub>

Germanium diselenide (GeSe<sub>2</sub>), a layered IV-VI semiconductor, has an in-plane anisotropic structure and a wide band gap, exhibiting unique optical, electrical, and thermal properties. In this paper, polarization axis Raman spectrum and linear absorption spectrum are used to characterize the crystal axis orientation and energy band characteristics of GeSe<sub>2</sub> flake, respectively. Based on the results, a micro-domain I scan system is used to study the optical nonlinear absorption mechanism of GeSe<sub>2</sub> near the resonance band. The results show that the nonlinear absorption mechanism in GeSe<sub>2</sub> is a superposition of saturation absorption and excited state absorption, and is strongly dependent on the polarization and wavelength of incident light. Under near-resonance excitation (450 nm), the excited state absorption is more greatly dependent on polarization. With different polarizations of incident light, the modulation depth can be changed from 4.6% to 9.9%; for non-resonant excitation (400 nm), the modulation depth only changes from 7.0% to 9.7%. At the same time, compared with saturation absorption, the polarization-dependent excited state absorption is greatly affected by the distance away from the resonance excitation wavelength.

NMR Investigation of the WTe2 Weyl Semimetal below the Topological Transition Temperature

NMR investigations are performed on 125Te nuclei of WTe2 Weyl topological semimetal at temperatures of 41 and 293 K. The measurements were carried out using a Bruker Avance 500 NMR pulse spectrometer. The 125Te NMR spectra for a WTe2 single crystal are obtained for the orientation of crystal axis c parallel and perpendicular to the quantizing field. A complicated form of the spectra was related to the presence of four nonequivalent positions of tellurium atoms in the crystalline structure of WTe2. The longitudinal magnetization recovery was studied after the pulse saturation for particular spectral lines. An exponential character of relaxation is revealed. The frequency shift and width of spectral lines were found to be insignificantly different at the two temperatures, while the times of nuclear spin-lattice relaxation at 41 K exceeded approximately by 30 times the corresponding times measured at room temperature. The strong temperature dependence of the relaxation is supposedly related to the contribution of the Weyl quasi-particles below the topological phase transition.

Rod-like incipient ferroelectric SrTiO3 polycrystal with crystal-axis orientation

Strontium titanate (SrTiO3, ST) is an incipient ferroelectric material. Generally, a one-dimensional (1D) ST polycrystal is difficult to obtain because of its high aspect ratio and directional orientation. We prepared a 1D ST polycrystal from a layered H2Ti4O9·H2O (HT) single crystal via a solvothermal soft chemical process. The 1D ST polycrystal fabricated from ST nanocrystals has a [010] crystal axis, implying that it is a mesocrystal. The ST nanocrystals were grown not only on the surfaces but also in the interlayers of the original HT matrix. The formation mechanism of the ST mesocrystal is based on a topochemical mesocrystal conversion process. ST ceramics fabricated from ST mesocrystal powder present a lossy capacitor response and excellent energy-storage capabilities owing to the presence of locally oriented ST nanocrystals with a lattice mismatch in the rod-like ST mesocrystals. The investigations performed in this study can set a new benchmark for the development of new electric ST-based materials.

Superlocalization and Formation of Grain Structure in Ni3ge Single Crystals with Different Orientations of Deformation Axes

The paper describes the influence of orientation of Ni3Ge single crystal deformation axes on the high-temperature superlocalization of plastic deformation. Mechanical properties of single crystals with different orientations are studied in this paper as well as the slip traces and the evolution of the dislocation structure. Based on these investigations, the observing conditions are described for the superlocalization bands and the formation of the grain structure in local areas of the original single crystal.

Crossover between Abrikosov vortex lattice and superconducting droplet state in superconductors with modulated disorder

We suggest a simple model describing the temperature-driven crossover between Abrikosov vortex lattice and superconducting droplet state in dirty superconductors with fluctuations either in the impurity concentration or in the crystal axes orientation. Our analysis is based on the Usadel-type theory with a spatially modulated diffusion coefficient. This modulation appears to break a regular vortex lattice into a random set of weakly coupled superconducting droplets emerging below the fluctuating upper critical field ${H}_{c2}(T)$. These droplets cause the resistivity drop at the onset of superconducting transition, being responsible for the increasing broadening of the resistive transition in the increasing magnetic field. The above crossover reveals itself in a positive curvature of the ${H}_{c2}(T)$ curves, allowing us, thus, to explain the phase diagrams observed in a wide class of disordered superconducting materials.