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The combined influence of spin–orbit coupling and spatial inversion asymmetry leads to an enhancement of electronic properties, including Rashba spin-splittings as well as spin Hall effect. Recent research has shown the possibility to create two-dimensional Janus materials with inherent structural asymmetry. In this work, the structural stability, piezoelectricity, electronic properties, and intrinsic spin Hall conductivity of quintuple-layer atomic Janus Sb2XSX' (X, X' = S, Se, Te; X ≠ X') monolayers are investigated using first-principles calculations within the framework of density functional theory. They demonstrate relatively high in-plane piezoelectric coefficients ( d 22) and also possess out-of-plane piezoelectric coefficients ( d 31), which is due to the breaking of inversion symmetry in the crystal structure with the space group P3m1. Large Rashba parameters are obtained in Janus Sb2XSX' monolayers, especially high for Sb 2 S 2 Te (1.62 eV Å) and Sb 2 SeSTe (1.33 eV Å) due to strong spin–orbit coupling. Moreover, Rashba-like spin-splitting is also observed in the edge-states as well, which is highest for Sb 2 SeSTe with 2.17 eV Å. Furthermore, Sb 2 S 2 Te and Sb 2 SeSTe monolayers reveal a significantly high Berry curvature (65.59 and 61.05 Bohr 2), spin Berry curvature (− 118.4 and − 120.6 Bohr 2), and spin Hall conductivity (1.8 and 1.6 e 2 /h). Our results suggest that Janus Sb 2 S 2 Te and Sb 2 SeSTe monolayers could be an excellent platform for multifunctional electronic applications. [ABSTRACT FROM AUTHOR]

Brillouin light scattering is a versatile measurement technique of the dispersion of bulk acoustic phonons in amorphous and crystalline solids. It allows contactless and non-destructive characterization of the relevant material tensors of optically transparent materials, provided that the optical refraction indices, and in addition the dielectric tensor for piezoelectric materials, are known beforehand. The complete estimation of the anisotropic material tensors is often performed using many different crystal orientations, and hence different samples of the same crystal. In this paper, we consider the problem of measuring those tensors using a single sample of an anisotropic single crystal with trigonal symmetry. A complete measurement requires sufficient experimental diversity in the phonon wavevectors when sampling the phonon velocity surfaces, hence the consideration of a large number of directions away from crystallographic axes. We estimate all six independent elastic constants of non-piezoelectric sapphire ( 3 ¯ m point group) with a single X-cut wafer and the six independent elastic constants together with the four independent piezoelectric constants of piezoelectric lithium niobate (3 m point group) with a single Y-cut wafer. The estimated tensors are in close agreement with those reported in the literature based on resonant ultrasonic techniques. [ABSTRACT FROM AUTHOR]

The all-temperature magnon (ATM) theory [Datta and A. Panda, J. Phys. Condens. Matter 21, 336003 (2009)] has been used to analyze the temperature dependence of magnetization and internal energy components of a mono-domain ferromagnetic solid. One impact of the ATM formulation is that calculated critical exponents are in better agreement with experiments than their counterparts from mean-field and critical phenomenon theories. These exponents can vary from one ferromagnet to another of similar symmetry and dimensionality but differing in spin and can be field-dependent. The ATM finding is that exponent β depends on spin and increases as T approaches TC, whereas the exponent γ is weakly dependent on spin and the applied field but relies on crystal symmetry. The main thrust of the present work has been to derive the thermally averaged spin-center force constants in terms of the baseline related (solid) and exchange-cum-field mediated (magnetic) components and to formulate phonon frequencies and their modifications by magnon–phonon coupling. The derived expressions are suitable for correct quantum chemical evaluation. A detailed calculation on different spin configurations at varying geometries is still hardly possible and beyond the scope of the present work that emphasizes the correctness of formulas and has the significance of explaining properties. The phonon frequency shift due to lattice expansion is always negative. It is also clarified that frequency modification by the magnon–phonon interaction is negative for certain phonon branches near TC, and the ratio of frequency modification and phonon frequency is approximately proportional to the ratio of curvatures of involved energy surfaces. [ABSTRACT FROM AUTHOR]

Antiferroelectric (AFE) materials are potentially useful for energy storage applications. Lead hafnate (PbHfO 3) is one of the prototypical AFE materials. However, its critical field (E cr) which is needed to induce the AFE to ferroelectric phase transition is close to the dielectric breakdown strength. To reduce E cr , we prepare the solid solutions of (1- x)PbHfO 3 – x BiAlO 3 (x = 0.00–0.04) via solid state synthesis. The crystal structures, dielectric behaviour, ferroelectric properties, and energy storage properties are investigated. A temperature-composition phase diagram is established. At room temperature, the crystal symmetry of all compositions is orthorhombic with the Pbam space group. Upon heating, the transition to the AFE orthorhombic Imma phase is observed at the temperature T C1 , which slightly decreases with increasing x , followed by the transition to the cubic phase at the temperature T C2 , which does not depend on x. Distinct dielectric anomalies are observed at T C1 and T C2. It is found that BiAlO 3 substitution reduces E cr and the polarization–electric field relations display characteristic double hysteresis loops. For x = 0.04, at a comparatively small applied field of 130 kV/cm, the values of recoverable energy density (W rec) and efficiency of 0.24 J/cm3 and 84 %, respectively, are obtained. At 190 °C, a W rec = 0.75 J/cm3 and a very high efficiency of 92 % are obtained at the field of 50 kV/cm. Thus, the prepared material can potentially be used in high-temperature pulsed power capacitors for energy storage applications within the temperature range from room temperature up to 190 °C. [ABSTRACT FROM AUTHOR]

This article investigates the dynamic features of domain walls in a bilayer piezoelectric-magnetostrictive heterostructure under the influence of piezo-induced strains, inertial damping, and dry friction dissipation. We assume that the magnetostrictive material belongs to the transversely isotropic hexagonal crystal. The analysis is carried out within the framework of the inertial Landau-Lifshitz-Gilbert equation, which describes the ultrafast evolution of magnetization inside the magnetostrictive materials. By employing the classical traveling wave ansatz, the study explores how various factors such as magnetoelasticity, dry friction, inertial damping, crystal symmetry, and a tunable external magnetic field characterize the motion of the magnetic domain walls in both steady-state and precessional dynamic regimes. The results present valuable insights into how these key parameters can effectively modulate dynamic features such as domain wall width, threshold, Walker breakdown, and domain wall velocity. The obtained analytical results are further numerically illustrated, and a qualitative comparison with recent observations is also presented. [ABSTRACT FROM AUTHOR]

Mid-infrared (MIR) light sources have gained significant importance across various applications in spectroscopy, sensing, astronomy, communications and medical surgery. The diverse spectral characteristics of rare earth ions, particularly lanthanide ions, stemming from their distinctive 4f intershell transitions, offer a multitude of potential transitions spanning the UV–visible–infrared spectrum. Despite recent advancements in MIR gain luminescence, the investigation of tunable MIR luminescence mechanisms remains a major technical challenge. Herein, an effective mechanism to modulate the local crystal field of rare earth ions by altering its crystal structure has been revealed, resulting in tunable broad-spectrum emission in the MIR luminescence range of 2800–3000 nm and multi-peak emission in the near-infrared band of Ho3+. Notably, the local crystal field of Ho3+ is adjusted by manipulating the lattice symmetry of CsPb 1-x Ho x Br 3 perovskite through the incorporation of fluoride glass reticulation to control the crystal size of the perovskite and thereby modify the lattice symmetry of CsPb 1-x Ho x Br 3 perovskite. The energy level transition of Ho3+ is influenced by adjusting the crystal field asymmetry, resulting in the splitting of the 5I 6 energy level depending on the crystal field. This cleavage affects the transitions from the 5I 5 level to 5I 6 at 1480 nm and from 5I 6 to 5I 7 at 2880 nm. As 5I 6 acts as the common upper level for the two emission peaks, the infrared peaks at 1480 nm and 2880 nm widen and develop into a dual-peak emission phenomenon. The infrared luminescence produced aligns closely with the distinctive infrared absorption peaks of carbon dioxide, leading to the development of a convenient, high-precision device for monitoring of CO 2 concentration in hydrogen energy in real time. These findings are anticipated to pave the way for extensive utilization of novel tunable MIR luminescence. [ABSTRACT FROM AUTHOR]

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Alloying/doping is a widely used technique for improving the electrical, mechanical, and optical properties of materials. However, this technology induces significant distortions in the lattice structure, mass distribution, and potential field, greatly enhancing phonon scattering. Here, we introduce the concept of alloying/doping path and employ crystal symmetry, lattice deformation, and electron distribution to characterize it. Based on this new concept, the phonon thermal transport behavior in alloyed/doped materials can be well designed, and along different alloying/doping paths, the difference in thermal conductivity can be up to 45 times. On one hand, strategic alloying/doping that combines high crystal symmetry, large lattice contraction, and the same electron distribution suppresses phonon-phonon scattering phase space, induces phonon stiffening, and bolsters electronic structure symmetry, respectively. These synergistic effects significantly improve thermal conductivity. On the other hand, random alloying/doping has a low symmetry, leading to the typical “U” shape of alloying/doping level-dependent thermal conductivity. Our theory is corroborated in three-dimensional (3D) Si, 2D MoS2, and quasi-1D TiS3, affirming its efficacy and broad applicability in controlling phonon transport. [ABSTRACT FROM AUTHOR]

Altermagnets (AM) are a recently discovered third class of collinear magnets and have been attracting significant interest in the field of condensed matter physics. Here, based on first-principles calculations and theoretical analysis, we propose four two-dimensional (2D) magnetic materials—monolayers V2Te2O, V2STeO, V2SSeO, and V2S2O—as candidates for altermagnetic materials. We show that these materials are semiconductors with spin-splitting in their nonrelativistic band structures. Furthermore, in the band structure, there is a pair of Dirac-type valleys located at the time-reversal invariant momenta (TRIM) X and Y points. These two valleys are connected by crystal symmetry instead of time-reversal symmetry. We investigate the strain effect on the band structure and find that uniaxial strain can induce valley polarization, topological states in these monolayer materials. Moreover, piezomagnetism can be realized upon finite doping. Our result reveals interesting valley physics in monolayers V2Te2O, V2STeO, V2SSeO, and V2S2O, suggesting their great potential for valleytronics, spintronics, and multifunctional nanoelectronics applications. [ABSTRACT FROM AUTHOR]

The Dzyaloshinskii-Moriya antisymmetric exchange interaction (DMI) stabilises topological spin textures with promising future spintronics applications. According to crystal symmetry, the DMI can be categorized as four different types that favour different chiral textures. Unlike the other three extensively-investigated types, out-of-plane DMI, as the last type that favours in-plane chirality, remained missing so far. Here we apply point-group-dependent DMI matrix analysis to show that out-of-plane DMI exists under reduced crystal symmetry. Through strain and structure engineering, we show how Cs symmetry is realized in ultrathin magnets and observe the out-of-plane DMI stabilised in-plane chirality using spin-polarized electron microscopy. Our results show that extremely low out-of-plane DMI strengths at µeV/atom are sufficient to stabilise topological spin textures, including merons and bimerons. We also demonstrate field-induced reversible control of the in-plane chirality and merons. Our findings open up untapped paths on topological magnetic textures and their potential applications. Antisymmetric exchange, or the Dzyaloshinskii-Moriya interaction, has been a topic intense study in recent years, due to its critical role in stabilizing topological spin-textures such as Skyrmions. Here, using a combination of point group analysis and spin polarized electron microscopy Niu et al demonstrate the existence of an out-of-plane Dzyaloshinskii-Moriya interaction, which was hitherto unobserved. [ABSTRACT FROM AUTHOR]

Symmetry invariants of a group specify the classes of quasiparticles, namely the classes of projective irreducible co-representations in systems having that symmetry. More symmetry invariants exist in discrete point groups than the full rotation group O(3), leading to new quasiparticles restricted to lattices that do not have any counterpart in a vacuum. We focus on the fermionic quasiparticle excitations under "spin-space group" symmetries, applicable to materials where long-range magnetic order and itinerant electrons coexist. We provide a list of 218 classes of new quasiparticles that can only be realized in the spin-space groups. These quasiparticles have at least one of the following properties that are qualitatively distinct from those discovered in magnetic space group(MSG)s, and distinct from each other:(i) degree of degeneracy,(ii) dispersion as function of momentum, and(iii) rules of coupling to external probe fields. We rigorously prove this result as a theorem that directly relates these properties to the symmetry invariants, and then illustrate this theorem with a concrete example, by comparing three 12-fold fermions having different sets of symmetry invariants including one discovered in MSG. Our approach can be generalized to realize more quasiparticles whose little co-groups are beyond those considered in our work. The symmetry of free space greatly restricts the properties of quasiparticles that exist in free space. Solid state systems, with the discrete symmetry of the crystal lattice, have far fewer restrictions, and here, Fang et al find a vast array of new quasiparticles, with distinct energy dispersions or external field couplings that can only be realised in the spin-space group. [ABSTRACT FROM AUTHOR]

The physical properties of two-dimensional (2D) van der Waals (vdW) materials are profoundly influenced by their stacking orders, which affect interlayer coupling and crystal symmetry, leading to fascinating strongly correlated orders. Detecting stacking orders is important, yet challenging as they involve sub-nanometer shifts in the relative arrangement of layers. In this study, we utilize nanomechanical resonators to detect the strain change during the stacking order transition of octahedrally coordinated thin molybdenum ditelluride (MoTe2) membranes and show the change in stacking orders can be reflected by the vibration modes of nanomechanical resonators. We discover that a strain as small as 0.014%—induced by transitions in the stacking order—results in a notable frequency shift up to 1.019 MHz in the mechanical resonance. We establish the relationship between the detection sensitivity of stacking orders and both internal and external parameters including higher-order vibrations, electrostatic energy, and initial strain. Our nanomechanical methodology offers a potential avenue for creating a comprehensive phase diagram by uncovering stacking orders across a wide array of van der Waals materials and leveraging ultralow-barrier stacking order transitions for energy-efficient devices. [ABSTRACT FROM AUTHOR]

Current induced spin–orbit torque (SOT) manipulation of magnetization is pivotal in spintronic devices. However, its application for perpendicular magnetic anisotropy magnets, crucial for high‐density storage and memory devices, remains nondeterministic and inefficient. Here, a highly efficient approach is demonstrated to generate collinear spin currents by artificial modulation of interfacial symmetry, achieving 100% current‐induced field‐free SOT switching in CoFeB multilayers with perpendicular magnetization on stepped Al2O3 substrates. This field‐free switching is primarily driven by the out‐of‐plane anti‐damping SOT generated by the planar spin Hall effect (PSHE), resulting from reduced interface symmetry due to orientation‐determined steps. Microscopic theoretical analysis confirms the presence and significance of PSHE in this process. Notably, this method for generating out‐of‐plane spin polarization along the collinear direction of the spin‐current with artificial modulation of interfacial symmetry, overcomes inherent material symmetry constraints. These findings provide a promising avenue for universal control of spin–orbit torque, addressing challenges associated with low crystal symmetry and highlighting its great potential to advance the development of energy‐efficient spintronic devices technology. [ABSTRACT FROM AUTHOR]

C points, circular polarization in momentum space, play crucial roles in chiral wave manipulations. However, conventional approaches of achieving intrinsic C points using photonic crystals with broken symmetries suffer from a low Q factor and high sensitivity to structural geometry, rendering them fragile and susceptible to perturbations and disorders. We report magneto-optical (MO) bound states in the continuum (BICs) with a symmetry-preserved planar photonic crystal. We achieve intrinsic C points at G point that are robust against variation in both structural geometry and external magnetic field. MO coupling between two modes induces Zeeman splitting, leading to MO BICs and quasi-BICs with circular eigenstates for high-Q chiral responses. Furthermore, switchable C point handedness and circular dichroism are enabled by reversing the magnetic field. These findings unveil BICs and quasi-BICs with circular eigenstates and on-demand control of C points, paving the way for advanced chiral wave manipulation with enhanced light-matter interaction. [ABSTRACT FROM AUTHOR]

Understanding the structure formation and its underlying physical mechanism is a fundamental topic in condensed matter systems, with both academic and practical implications. Soft matter is playing a remarkable role in current era of information explosion, demonstrating enormous potential in integrated functional photonics. As unique soft photonic crystals with cubic symmetries, not only liquid crystalline blue phases (BPs) have circularly polarized selective reflection and ultra-fast electro-optical response, but also their three-dimensional photonic structures increase degrees-of-freedom for multiplexed optical modulation. In the thriving field of soft-matter-based photonics, precise and programmable engineering of BP crystal orientation is of vital importance for planar optical elements, which remains a challenging task due to the complexity of the nucleation process as well as the interaction between the BP building blocks and the boundary conditions. Aiming to gain a comprehensive understanding of how to tailor the orientation of BP crystals for the photonic applications of next generation, here we discuss the solutions for uniformity improvement and orientation control of BP crystals, about which a few of examples in combination with the underlying mechanisms are explained. In addition, the remaining challenges and the efforts that are expected are also reviewed. We expect this work provides a deeper understanding of phase transitions and resulting structures in soft crystals, which may open encouraging perspectives for their applications in photonics, biosensing, interfacial, and chemical engineering. [ABSTRACT FROM AUTHOR]

Current semiconductor qubits rely either on the spin or on the charge degree of freedom to encode quantum information. By contrast, in bilayer graphene the valley degree of freedom, stemming from the crystal lattice symmetry, is a robust quantum number that can therefore be harnessed for this purpose. The simplest implementation of a valley qubit would rely on two states with opposite valleys as in the case of a single-carrier bilayer graphene quantum dot immersed in a small perpendicular magnetic field (B⊥ ≲ 100 mT). However, the single-carrier quantum dot excited states spectrum has not been resolved to date in the relevant magnetic field range. Here, we fill this gap, by measuring the parallel and perpendicular magnetic field dependence of this spectrum with an unprecedented resolution of 4 μeV. We use a time-resolved charge detection technique that gives us access to individual tunnel events. Our results come as a direct verification of the predicted spectrum and establish a new upper-bound on inter-valley mixing, equal to our energy resolution. Our charge detection technique opens the door to measuring the relaxation time of a valley qubit in a single-carrier bilayer graphene quantum dot. A single electron quantum dot in bilayer graphene is a candidate for a spin-valley qubit, however its excited state spectrum has not been determined under relevant conditions. Here the authors accomplish this using time-resolved charge detection technique and set the new upper bound on the inter-valley mixing. [ABSTRACT FROM AUTHOR]

In this study, the propagation of plane waves in the lanthanum gallium tantalate (langatate, LGT) single crystals is investigated. Moreover, the flight time of different waves in the LGT rectangular parallelepiped sample is measured using the ultrasonic pulse‐echo (UPE) technique, and the elastic constants of the LGT sample are determined. The experimental results clearly show echoes corresponding to the longitudinal and transverse waves along the x‐axis. The waves along the z‐axis have a similar property. However, the waves along the y‐axis are more complex than those along the x‐ and z‐axes. The echoes corresponding to the quasi‐longitudinal waves along the y‐axis are clear, but those corresponding to the transverse and quasi‐transverse waves along the y‐axis are not. The elastic constant can be accurately determined if the wave echoes corresponding to this constant propagate without distinct distortion and are clear; otherwise, it may be impossible to accurately determine the constant using UPE. All elastic constants cijE$c_{ij}^{\mathrm{E}}$ except c13E$c_{13}^{\mathrm{E}}$ of the LGT single crystals can be determined using UPE from one sample. This study uses UPE to provide a reference for the characterization of elastic constants of piezoelectric crystals with 32 symmetry from one sample. [ABSTRACT FROM AUTHOR]

Focusing on a VGa–VN complex vacancy defect in GaN, the adiabatic potential for conformational changes of the VGa–VN is investigated using the density functional theory. There are two types of configurations due to the symmetry of the crystal, it is confirmed that there is almost no difference in their stability or electronic state. Using these configurations as the initial and final states, the defect reaction is analyzed when VGa–VN moves using the climbing‐image nudged elastic band method. The reaction barrier for the migration of VGa (VN) is found to be 2.2 (3.3) eV. It is concluded that these reactions occur frequently as GaN is annealed since the atomic diffusion potential barrier is similar to that in other semiconductors. These results suggest that VGa–VN in GaN moves through the crystal as a pair of vacancies by alternately repeating the VGa and the VN migration. These results provide important knowledge for elucidating the microscopic mechanism of the experimentally observed VGa–VN aggregation reaction. [ABSTRACT FROM AUTHOR]

Narrow‐band cyan‐emitting materials for white light‐emitting diode (wLED) application have shown great potential in increasing the maximum accessible display gamut and improving the color rendering of full‐spectrum healthy lighting. However, the discovery of novel narrow‐band cyan emitters with excellent luminescence performances remains challenging. Here, an ultra‐narrow‐band cyan‐emitting Na5K3(Li3SiO4)8:Eu2+ (N5K3:Eu2+) phosphor (λem = 483 nm) with full width at half maximum (FWHM) of only 18 nm is developed from some typical UCr4C4 frameworks phosphors by slightly modifying crystal structure and symmetry. Through controllable regulation of the ratio of Na and K from Na4K4(Li3SiO4)8:Eu2+ (N4K4:Eu2+) and Na6K2(Li3SiO4)8:Eu2+ (N6K2:Eu2+) to N5K3:Eu2+, the lattice sites forming shoulder peaks are further squeezed to generate the narrowest cyan emission. Moreover, the N5K3:Eu2+ exhibits low photoluminescence thermal quenching (90%@150 °C) and high internal quantum efficiency (IQE) of 50%. The color rendering index of wLED for full‐spectrum health lighting is enhanced from 92 to 94. Using this short‐wavelength cyan emission instead of a part of the emission from a blue chip can effectively prevent "blue hazard". This work provides basic principles for the design of ultra‐narrow‐band phosphors, thus achieving their applications in the fields of healthy lighting and eye‐friendly display. [ABSTRACT FROM AUTHOR]

In this study, the effect of elastic biaxial strain on electronic structure and the anomalous Hall conductivity (AHC) of α‐Fe has been systematically studied by using the combination of a first principles calculation with the tight binding method through the Wannier function. It is found that applying strain in cubic structure of α‐Fe results in the reduction of crystal symmetry and gives the modification on the bands near Fermi level, which causes a significant change in the AHC of strained systems. The AHC of strained α‐Fe is found to be sensitive with applying strain, which shows the large enhancement of AHC at +2% tensile strain with AHC value is up to 929 Ω−1 cm−1 (increases more than 30%) compared with the unstrained one, while slightly reduces when applying compressive strain. The modification of AHC is found to be related to the change of Berry curvature contributed from the spin orbit coupling (SOC) induced energy gap near Fermi level. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Resonant inelastic X-ray scattering (RIXS) has played a pivotal role in advancing our understanding of spin-orbit physics in 5d transition metal materials. The progress in RIXS techniques has closely paralleled improvements in energy resolution, which have enabled the study of very low-lying excitations and led to the discovery of numerous new phenomena with significant scientific and technological implications. The multi-bend achromat (MBA) lattice upgrade of third-generation synchrotron sources, such as the Advanced Photon Source (APS), heralds a transformative era by introducing enhancements in brilliance and emittance. These advancements provide an opportunity to push the boundaries of RIXS techniques, meeting the challenges at the research frontiers of material science. This article aims to highlight key instrumental and technical advancements that enable the achievement of meV resolution in RIXS and discuss the impact of such high-resolution RIXS on exploring spin-orbit physics in 5d transition metal materials. [ABSTRACT FROM AUTHOR]

Nine different derivatives of piperidino alanes of the general formula (CH2)5N‐AlXY [X=Y=Cl (1), Br (2), I (3); X=(CH2)5N, Y=Cl (4), Br (5), I (6); X=H, Y=Cl (7), Br (8), I (9)] have been synthesized and compared with respect to their structures. All molecules form dimers with an Al2N2 central cycle and aluminum and nitrogen atoms in distorted tetrahedral environments as determined from X‐ray diffraction. The three dihalide derivatives 1, 2 and 3 have C2h (2/m) symmetries in solution of which they maintain the Centro symmetry in the crystal lattice. The bis(piperidino) derivatives 4, 5 and 6 have either C1 (1) symmetry with the bridging piperidino cycles oriented in the same direction (4, 5) or Ci (ī) point symmetry as found for 6 (in solution at least one other isomer is present). Whereas the chlorine derivative 7 has crystallographic Ci (ī) symmetry, the bromine 8 has almost C2 and the iodine 9 crystallographic C2 (2) point symmetry. In solution all derivatives 7, 8, 9 show equilibria between cis (C2) and trans (Ci) isomeric forms (27Al NMR). The longest Al−N bond lengths within the rings are found for 5 (1.969(4) Å) and the shortest for 8 (1.940(4) Å). The ratio of Al⋅⋅⋅Al to N⋅⋅⋅N non‐bonding distances in the almost square rings vary with the bulkiness of the terminal ligands at aluminum. [ABSTRACT FROM AUTHOR]

In recent years, dislocation‐tuned functionalized ceramics have become one of the focal points of modern materials research due to their outstanding properties. These range from improved electrical conductivity and ferroelectric properties to dislocation‐enhanced toughening and superconductivity, caused by local strain fields. The aim of this work is to investigate the dislocation‐induced structural changes in single‐crystal KNbO3 by micro‐Raman spectroscopy. Dislocation‐rich regions with tailored densities have been generated using the Brinell indenter scratching method. The influence of the dislocations on the single‐crystal structure can be observed in the Raman spectra. The activation of additional Raman modes is observed, which does not occur in regions of low dislocation density. This observation is confirmed by DFT calculations of vibrational modes and is attributed to a reduction in the crystal symmetry due to increased defect densities in plastically deformed KNbO3. In addition, an increase in compressive stress at higher dislocation densities can be demonstrated by a blueshift in Raman mode positions. [ABSTRACT FROM AUTHOR]

Resonant inelastic X-ray scattering (RIXS) has played a pivotal role in advancing our understanding of spin-orbit physics in 5d transition metal materials. The progress in RIXS techniques has closely paralleled improvements in energy resolution, which have enabled the study of very low-lying excitations and led to the discovery of numerous new phenomena with significant scientific and technological implications. The multi-bend achromat (MBA) lattice upgrade of third-generation synchrotron sources, such as the Advanced Photon Source (APS), heralds a transformative era by introducing enhancements in brilliance and emittance. These advancements provide an opportunity to push the boundaries of RIXS techniques, meeting the challenges at the research frontiers of material science. This article aims to highlight key instrumental and technical advancements that enable the achievement of meV resolution in RIXS and discuss the impact of such high-resolution RIXS on exploring spin-orbit physics in 5d transition metal materials. [ABSTRACT FROM AUTHOR]

How to break the C═O bond and reduce the energy barrier of *COOH formation is the key to triggering the photocatalytic CO2 reduction (PCR) reaction and subsequent proton‐electron processes, which is as important as overcoming high recombination rate of photocarriers. In order to solve this issue, the symmetric structure of CuS/TiO2 is destroyed by S vacancy and Al doping (denoted as Al‐CuS/TiO2), which significantly expands the electron localization range and promotes the cis‐coordination splitting of Cu 3d orbits. The experimental results show that the CO yield selectivity of ≈90.68% and yield of ≈335.68 µmol·g−1·h−1 on Al‐CuS/TiO2. The redistribution of Cu electron states in specific d/s/p orbitals increases the adsorption of CO2 and reduces the reaction energy barrier of *COOH intermediates, while effectively breaking the C═O bond. Doped Al atoms also serve as adsorption sites for H2O molecules, effectively interleaving the competition with photocatalytic CO2 reduction at the Cu sites is effectively staggered. This study provides a new approach to reduce the energy barrier of *COOH formation and to accelerate the photocarrier migration by destroying local symmetry to adjust the crystal structure, which is important for further improving the activity and selectivity of PCR. [ABSTRACT FROM AUTHOR]

In the classical model, ferroelectricity is associated with small ion displacements from paraelectric phases with high symmetry, and ferroelectric crystals must adopt one of the ten polar point groups with low symmetry according to Neumann's principle. In this work, it is proposed that this conclusion is based on perfect bulk crystals without taking the boundaries into account. First‐principles evidence shows that ferroelectric polarizations may also be formed in some non‐polar point groups as the edges generally break the crystal symmetry. Meanwhile, such polarizations can be maintained at macroscale and are switchable when the transition between multiple equivalent states with high symmetry can be realized via long ion displacements， essentially akin to ion conductors. For example, the switching barriers can be much reduced in sliding ferroelectric bilayer systems or ionic compounds with covalent‐like directionality. Such unconventional ferroelectricity can be attributed to the boundaries and long ion displacements, and its existence in several systems like CuCrS2 is supported by experimental observations. It may explain a series of unclarified phenomena reported previously as well as significantly expand the scope of ferroelectrics, especially those with high polarizations induced by long ion displacements. [ABSTRACT FROM AUTHOR]

How to break the C═O bond and reduce the energy barrier of *COOH formation is the key to triggering the photocatalytic CO2 reduction (PCR) reaction and subsequent proton‐electron processes, which is as important as overcoming high recombination rate of photocarriers. In order to solve this issue, the symmetric structure of CuS/TiO2 is destroyed by S vacancy and Al doping (denoted as Al‐CuS/TiO2), which significantly expands the electron localization range and promotes the cis‐coordination splitting of Cu 3d orbits. The experimental results show that the CO yield selectivity of ≈90.68% and yield of ≈335.68 µmol·g−1·h−1 on Al‐CuS/TiO2. The redistribution of Cu electron states in specific d/s/p orbitals increases the adsorption of CO2 and reduces the reaction energy barrier of *COOH intermediates, while effectively breaking the C═O bond. Doped Al atoms also serve as adsorption sites for H2O molecules, effectively interleaving the competition with photocatalytic CO2 reduction at the Cu sites is effectively staggered. This study provides a new approach to reduce the energy barrier of *COOH formation and to accelerate the photocarrier migration by destroying local symmetry to adjust the crystal structure, which is important for further improving the activity and selectivity of PCR. [ABSTRACT FROM AUTHOR]

It is well known that the properties of a crystal evolve as it increases in size from a single atomic plane to that of the bulk. Such size‐dependent transitions can stem from many different origins and depend on minute changes to crystal bonding and composition. A model example is that of LaCoO3, which is non‐magnetic in the bulk but can display ferromagnetism at the nanoscale. Here, the evolution of structure‐property relationships is studied in the LaCoO3−δ/SrTiO3 (001) system as the thickness of LaCoO3−δ is increased from a single plane to 10 unit cells. In situ synchrotron X‐ray studies are performed during and post‐deposition to probe changes in the interactions between structure, stoichiometry, and magnetic behavior. Structural quantification indicates that the oxygen octahedral rotation pattern evolves with thickness, due to inherent differences in crystal symmetry between the film and substrate. The change in rotation modifies the required energy barrier for the spin state transition via the Co–O bond length and Co–O–Co bond angle, affecting the appearance of ferromagnetism. Our results highlight the contributions of high spin Co2+ and/or high spin Co3+ to respective weak and robust ferromagnetism and the evolution of properties with size in ultrathin LaCoO3−δ heterostructures. [ABSTRACT FROM AUTHOR]

Magneto-electric effect, i.e. an appearance of magnetisation induced by electric current, is allowed by symmetry in metals with crystal structure without space inversion. The microscopic origin of this effect is spin–orbit coupling of electrons with a non-centrosymmetric crystal lattice lifting spin degeneracy of electron energy and mixing spin and orbital degrees of freedom. The presented here calculation of magnetisation induced by current is based on the application of kinetic equation for the matrix distribution function of electrons occupying the states in two bands split by the spin–orbit interaction. [ABSTRACT FROM AUTHOR]

This study investigates the pressure-dependent thermal and mechanical properties of solid bromine through density functional theory (DFT) calculations used in conjunction with the quasi-harmonic approximation (QHA). At ambient pressure, bromine crystallizes as a molecular crystal of Cmca symmetry. Previous studies have indicated that upon compression, this polymorph should undergo a bandgap closure at 80 GPa followed by a phase transition to a nonmolecular phase at 90 GPa. By employing QHA, we model the lattice vibrations and calculate the free energy, thermal expansion, and specific heat capacities of solid molecular bromine over a temperature range from 0 to 1000 K and pressures up to 90 GPa. Furthermore, mechanical properties such as bulk modulus and elastic constants are also analyzed. The results reveal the significant impact that pressure has on the thermal properties, mechanical stability, and dynamical stability of a molecular crystal. These findings contribute to a deeper understanding of such systems under extreme conditions, potentially guiding future experimental and theoretical investigations. [ABSTRACT FROM AUTHOR]

Morphology‐controlled Cs2SbBr6 crystals are synthesized by Bi‐ and Ag‐substitution of the precursor solution. X‐ray diffraction (XRD) together with Raman spectroscopy confirms the lattice tilting and symmetry changes with the dominant appearance of higher index facets by Bi substitution. Ag substitution does not induce crystal symmetry changes in the Cs2BBr6 (B = Sb or Bi) phase, but results in highly defective structures hindering the formation of a smooth surface during the crystal growth. Successful substitution of Bi and limited substitution of Ag into Cs2SbBr6 is also confirmed by energy dispersive X‐ray spectroscopy (EDX). This research provides design principles and practical examples of how to control the morphology of Cs2SbBr6 crystals with structural defects and multiphase formation. [ABSTRACT FROM AUTHOR]

An exhaustive search for missing symmetry was performed for 223076 entries in the ICSD (2023‐2 release). Approximately 0.65% of them can be described with higher symmetry than reported. Out of the identified noncentrosymmetric entries, ∼74% can be described by centrosymmetric space groups; this has implications for compatible physical properties. It is proposed that the information on the correct space group is included in the ICSD. [ABSTRACT FROM AUTHOR]

The study focused on the nitrilo‐tris‐(methylene phosphonate) [K2ntpH4]2 and [(K1−yTly)2ntpH4]2 complexes, which are a series of isovalent substitutions. The crystals of [K2ntpH4]2 are monoclinic and belong to the space group of symmetry P21/c with Z=4. When thallium substitutes potassium, the molecular structure remains the same, but the symmetry of the crystal packing changes to a triclinic system, space group of symmetry P1‾ ${\bar{1}}$ , with Z=2. One coordination polyhedra maintains an isometric configuration, while the other undergoes significant distortions. Polarization‐selective coordination is observed, where the thallium(I) ion, which is easily polarizable, populates the highly distorted polyhedron. The low polarizable potassium ion populates the weakly distorted one. The crystal is formed with an average thallium fraction higher than the initial aqueous solution. This suggests that replacing potassium ions in the complex with thallium ions is energetically favourable. It could explain why thallium is toxic to intracellular enzymes and carriers of genetic information. The isovalent substitution of potassium made it possible to observe the step‐by‐step formation of a super‐strong hydrogen bond, a phenomenon that is rarely detected under normal conditions. The O...O interatomic distance in the hydrogen bond decreases gradually from 2.55 Å for [K2ntpH4]2 to 2.474 Å for [Tl2ntpH4]2. [ABSTRACT FROM AUTHOR]

Recently a large variety of non‐collinear spin textures have been revealed in various crystals with different symmetry groups. Of particular interest are crystals with D2d symmetry that exhibit a complex variety of stable and metastable spin textures that includes antiskyrmions, elliptical Bloch‐skyrmions, fractional‐antiskyrmions, fractional Bloch‐skyrmions, and type‐II trivial‐bubbles. The observation of these structures necessitates their stabilization via magnetic field and temperature protocols which demands a thorough understanding of their creation, transformation, and collapse dynamics. Utilizing the real‐space imaging capabilities of Lorentz transmission electron microscopy, the generation and annihilation of diverse spin textures in a single D2d Heusler compound are demonstrated. It is showed that antiskyrmions and elliptical Bloch‐skyrmions can be deformed into more elaborate elongated magnetic nano‐objects through a collapse mechanism. Their elongation is governed by the intrinsic antisymmetric Dzyaloshinskii‐Moriya vector exchange interaction and dipolar energy present in the system. Furthermore, antiskyrmions are found to be metastable at all temperatures on field‐cooling, while a topological phase transformation from elliptical Bloch‐skyrmions to antiskyrmions rather takes places on field‐heating. These results are corroborated by micromagnetic simulations and demonstrate the efficient manipulation of different spin textures in a D2d compound by varying field and temperature protocols and represents a critical step toward the application of magnetic skyrmions. [ABSTRACT FROM AUTHOR]

Ceria has attracted a lot of interest in scientific community due to its several technological uses. During this study, composite hydroxide-mediated method was used to prepare nanocubes of undoped and doped ceria. The prepared materials were characterized using a number of analytical techniques including room temperature powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) theory, and UV–Visible spectroscopy to investigate the structural, morphological, optical and photocatalytic properties. No impurity phases were observed from the XRD revealing face centred cubic (FCC) crystal symmetry of the undoped and doped ceria. The formation of nanocubes was confirmed by SEM. Pore sizes in the range of 24.9–29 mm were revealed by BET analysis. A gradual increase in photodegradation efficiency with an increase in irradiation time was seen for the doped samples compared to undoped ceria, showing suitability for photocatalytic applications. An increase in defect concentrations especially for Sr2+ doped samples indicated by the quantitative analysis of Raman spectra reveals potential for electrolytic applications in fuel cells provided necessary conductivity and long-term performance testing would need to be done. [ABSTRACT FROM AUTHOR]

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Research on intragranular acicular ferrite inclusions has demonstrated that high-melting-point oxide MgAl2O4 cores and composite inclusions precipitated by Ti2O3 adhesion can be used as effective nucleation particles in oxide metallurgy. However, the microscopic mechanism underlying this adsorption behavior remains unclear. Hence, in this study, the adsorption and polymerization mechanisms of Ti2O3 on the MgAl2O4(100)Mg- and MgAl2O4(111)O3(Mg)-terminal surfaces in steel were studied using first-principles calculations based on density functional theory. The calculation based on the first principles of DFT and performed by the CASTEP code under plane wave basis set. The exchange correlation energy and correlation effects were described by generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) function. Spin polarization was considered in all calculation. Ultrasoft pseudopotentials (USPP) was employed to describe the electron-ion interactions. The energy cutoff for the plane wave basis was set at 620 eV in the current work. For the Brillouin zone sampling, we carried out 3 × 3 × 3 k-points mesh for MgAl2O4 bulk using the method of Monkhorst-Pack. A vacuum layer of 20.0 Å is added above the top surface of MgAl2O4 to eliminate the interaction of the normal periodic repetition of the surfaces. In all the surface calculations, the use of symmetry in bulk crystal was failed and k-point grids is set to 3 × 3 × 1. The results of this study revealed that when the most stable adsorption positions of Ti2O3 on the surface of MgAl2O4(100)Mg- and MgAl2O4(111)O3(Mg)-terminal are located at TAl and FMg, the adsorption energy is the highest and the most stable. The most stable adsorption configurations are located on vertical and parallel (P1) surfaces. Through comparative analysis, the best surface for Ti2O3 adsorption was found to be the MgAl2O4(111)O3(Mg)-terminal surface, and the adsorption behavior mainly occurred on the first layer of atoms on the surface. The best adsorption configuration was P1, and the best adsorption mode occurred when Ti2O3 formed three rings connected in pairs with the surface and embedded in the surface of the MgAl2O4(111)O3(Mg)-terminal. This study provides insights into the adsorption polymerization mechanisms of MgAl2O4–Ti2O3 complex inclusions in steel that could facilitate the fabrication of novel low-melting-point oxides and sulfides. [ABSTRACT FROM AUTHOR]

Thouless charge pumps are quantum mechanical devices whose operation relies on topology. They provide the means for transporting quantum matter in space lattices with a single quantum precision. Contrasting space crystals that spontaneously break a continuous spatial translation symmetry and form crystals in space, time crystals have emerged as novel states of matter that organise into time lattices and spontaneously break a discrete time translation symmetry. The utility of Thouless pumps that enable topologically protected quantised transport of electrons and neutral atoms in spatial superlattices leads to the question if corresponding devices exist for time crystals. Here we show that topological pumps can be realised for time solids by transporting droplets of a liquid forward and backward in time lattices and we measure the topological index that characterises such pumping processes. By exploiting a synthetic time dimension, classical time crystals can circumvent the quantum tunnelling that underpins Thouless charge pumps. Our results establish topological pumping through time instead of space and pave the way for applications of time crystals. Key Points: Periodically driven fluid droplets can be made to bounce persistently in a gravitational field and may undergo spontaneous time translation symmetry breaking forming classical time crystals.These classical time crystals can be pumped from one time site to another, and this pumping process is characterised by a topological index.Our observations establish a classical temporal counterpart to Thouless pumping of quantum particles in space lattices. [ABSTRACT FROM AUTHOR]

Thin layers of ferromagnetic/non-magnetic bimetallic heterostructures have become the focal point of spintronics, primarily due to their capacity to convert spin to charge current, leveraging the spin- and inverse spin Hall effects. However, the interfacial properties and morphologies can significantly influence this conversion. Hence, we employed molecular dynamics calculations to model the construction of the Fe/Pt interface at various bilayer growth temperatures and Pt deposition rates. We then experimentally evaluated the modeling using x-ray methods to resolve the chemical and structural state of the interface. The calculations revealed moderate diffusive phenomena between the adjacent layers and an interfacial roughness of less than 1 nm, consistent with the experimental observations. In cases where plastic relaxation of the Fe/Pt interface is insufficient, lattice deformation is mitigated by a local pseudomorphic growth caused by transformation of the Pt crystal symmetry. Additionally, interfacial planar defects may emerge as a complementary stress-relieving mechanism to misfit dislocations. By combining the experimental and computational findings, we propose optimized growth conditions for an "ideal" Fe/Pt interface, which could serve as a useful tool to control the efficiency of spin-to-charge conversion. [ABSTRACT FROM AUTHOR]

Using muon spin relaxation measurements on formamidinium lead iodide [ FAPbI 3 , where FA denotes HC( NH 2) 2 ], we show that, among the five structurally distinct phases of FAPbI 3 exhibited through two different temperature hysteresis, the reorientation motion of FA molecules is quasi-static below ≈ 50 K over the time scale of 10 − 6 s in the low-temperature (LT) hexagonal (Hex-LT, <160 K) phase, which has a relatively longer photo-excited charge carrier lifetime (τ c ∼ 10 − 6 s). In contrast, a sharp increase in the FA molecular motion was found above ≈ 50 K in the Hex-LT phase, LT-tetragonal phase (Tet-LT, <140 K), the high-temperature (HT) hexagonal phase (Hex-HT, 160–380 K), and the HT-tetragonal phase (Tet-HT, 140–280 K), where τ c decreases with increasing temperature. More interestingly, the reorientation motion is further promoted in the cubic phase at higher temperatures (>380/280 K), while τ c is recovered to comparable or larger than that of the LT phases. These results indicate that there are two factors that determine τ c , one related to the local reorientation of cationic molecules that is not unencumbered by phonons and the other to the high symmetry of the bulk crystal structure. [ABSTRACT FROM AUTHOR]

Using muon spin relaxation measurements on formamidinium lead iodide [ FAPbI 3 , where FA denotes HC( NH 2) 2 ], we show that, among the five structurally distinct phases of FAPbI 3 exhibited through two different temperature hysteresis, the reorientation motion of FA molecules is quasi-static below ≈ 50 K over the time scale of 10 − 6 s in the low-temperature (LT) hexagonal (Hex-LT, <160 K) phase, which has a relatively longer photo-excited charge carrier lifetime (τ c ∼ 10 − 6 s). In contrast, a sharp increase in the FA molecular motion was found above ≈ 50 K in the Hex-LT phase, LT-tetragonal phase (Tet-LT, <140 K), the high-temperature (HT) hexagonal phase (Hex-HT, 160–380 K), and the HT-tetragonal phase (Tet-HT, 140–280 K), where τ c decreases with increasing temperature. More interestingly, the reorientation motion is further promoted in the cubic phase at higher temperatures (>380/280 K), while τ c is recovered to comparable or larger than that of the LT phases. These results indicate that there are two factors that determine τ c , one related to the local reorientation of cationic molecules that is not unencumbered by phonons and the other to the high symmetry of the bulk crystal structure. [ABSTRACT FROM AUTHOR]

An aliovalent metal substitution strategy was proposed in preparing MOF hybrid membranes with high chemical stability and proton conductivity. With the aliovalent substitution of In(III) for Cd(II), both the metal–oxygen coordination bond energy strength and the unit cell symmetry of the model gradually raised, resulting in the thermal stability increase of Im@quasi- C -In-BTC (C 3 H 5 N 2) 2 [In(BTC)] reach up to 700 K, as well as exhibiting a super protonic performance with the proton conductivity of 7.1 × 10−2 S cm−1 at 65 °C and 95 % relative humidity. Furthermore, Im@quasi- C -In-BTC was hybridized with poly(vinyl pyrrolidone)-poly(vinylidene fluoride) polymer to synthesize into Im@quasi- C -In-BTC@PP-X (X = 20, 40, 60) membrane, implying its enormous potentiality for proton exchange membrane applications. [Display omitted] • An aliovalent metal substitution strategy was implemented in symmetry-related highly stable proton-conducting MOFs. • The synergistic effect of contracted pore volume and encapsulated imidazolium cations in Im@quasi- C -In-BTC enhanced its conductivity. • High stability was obtained through a good integration of strong coordination bond and significant steric hindrance. • The prepared MOF membrane was expected to be developed into proton exchange membrane fuel cells. Proton-conducting materials have gained popularity owing to their extensive applications in biologic/chemical sensors, supercapacitors, proton sieving, and proton-exchange-membrane fuel cells. To date, the most commercially used polymer membrane has been the Nafion series that exhibits conductivity exceeding 0.1 S cm−1, however, this series is expensive, has poor dimensional stability, and requires a complex synthesis process. The key criterion for selecting Nafion alternatives is to achieve the systematic integration of high proton conductivity with high stability through a simple and efficient approach. In this study, we used an aliovalent metal substitution strategy to design serial metal–organic frameworks (MOFs), including tetragonal T -Cd-BTC (CH 3 NH 2 CH 3) 2 [Cd(BTC)](H 2 O) and quasi-cubic quasi- C -In-BTC (C 4 H 7 N 2)[In(BTC)] and Im@quasi- C -In-BTC (C 3 H 5 N 2) 2 [In(BTC)] frameworks, with 2-methylimidazolium and imidazolium cations as templates, respectively. Because of the aliovalent substitution of In(III) for Cd(II), both the metal–oxygen bond strength and unit cell symmetry gradually increased, resulting in an increase in the thermal stability of quasi- C -In-BTC and Im@quasi- C -In-BTC at temperatures of up to 700 K. Compared with in situ loaded 2-methylimidazolium quasi- C -In-BTC, Im@quasi- C -In-BTC prepared by incorporating the imidazolium cation into the pores of activated quasi- C -In-BTC exhibited a higher proton conductivity of 7.1 × 10−2 S cm−1 at 338 K and 95 % relative humidity. Thus, Im@quasi- C -In-BTC demonstrated real-life application. This result was confirmed by integrating Im@quasi- C -In-BTC with a poly(vinyl pyrrolidone)-poly(vinylidene fluoride) polymer matrix. Density functional theory simulations indicated that Im@quasi- C -In-BTC was strongly acidic and had high water–adsorption capacities, which contributed to extensive hydrogen-bond networks and strong host–guest interactions, in accordance with the experimental finding. [ABSTRACT FROM AUTHOR]

We study the evolution of band topology under external pressure in rare-earth gadolinium mono-antimonide (GdSb) using first-principles calculations. This material crystallizes in a rocksalt-type structure and shows a structural phase transition (SPT) to a CsCl-type structure at 26.1 GPa. The phonon dispersions are analyzed to ascertain the dynamical stability of this material. We use hybrid density functional theory with the inclusion of spin–orbit coupling to investigate the structural, electronic, and topological phase transitions (TPTs). At ambient pressure, GdSb shows a topologically trivial state which is in agreement with existing experimental reports. The first TPT is observed at 6 GPa of hydrostatic pressure (at the high symmetry X -point) which is verified with the help of single-band inversion and surface state analysis along the (001) plane. The non-zero value of the first Z2 topological invariant and the presence of the Dirac cone also confirm the topological phase of this material. A further increase in pressure to 12 GPa results in two band inversions at Γ - as well as X - points, which corresponds to the trivial nature of GdSb. The same is also verified with (0; 000) values of Z2 topological invariants and a pair of Dirac cones in surface states. It is noted that the crystal symmetries are preserved throughout the study and the TPT values are much lower than the SPT pressure, i.e. 26.1 GPa. [ABSTRACT FROM AUTHOR]

Organic-cation engineering has recently proven effective in flexibly regulating two-dimensional hybrid organic–inorganic perovskites (2D HOIPs) to achieve a diversity of newly emerging applications. There have been many mechanistic studies based on the structural tunability of organic cations; nevertheless, those with an emphasis on the effect solely caused by the organic cations remain lacking. To this end, here we deliberately design a set of 2D HOIPs in which the inorganic layers are kept nearly intact upon cation modification, i.e., the precursor phenethylammonium lead iodide and its four derivatives with the phenyl group's para-position H being replaced by CH3, F, Cl, and Br. By means of femtosecond time-resolved transient absorption spectroscopy and temperature-dependent/time-resolved photoluminescence spectroscopy, we interrogate the subtle impact of cation modification on phonon dynamics, coherent phonon modes, phonon-dressed exciton dynamics, and excitonic emissions. A concerted trend for phonon lifetimes and exciton relaxation lifetimes regulated by cation modification is revealed, evidencing the existence of strong exciton–phonon coupling in this 2D HOIP system. The observed mass effect can be ascribed to the change in moment of inertia of organic cations. In addition, we observe an interesting interplay of exciton kinetics pertinent to population transfers between two emissive states, likely linked to the subtle variation in crystal symmetry induced by cation modification. The mechanistic insights gained from this work would be of value for the 2D HOIPs-based applications. [ABSTRACT FROM AUTHOR]

Materials exhibiting a spontaneous reversal of spin chirality have the potential to drive the widespread adoption of chiral magnets in spintronic devices. Unlike the majority of chiral magnets that require the application of an external field to reverse the spin chirality, we observe the spin chirality to spontaneously reverse in the topological magnet EuAl4. Using resonant elastic x-ray scattering we demonstrate that all four magnetic phases in EuAl4 are single-k, where the first two magnetic phases are characterized by spin density wave order and the last two by helical spin order. A single spin chirality was stabilised across the 1mm2 sample, and the reversal of spin chirality occurred whilst maintaining a helical magnetic structure. At the onset of the helical magnetism, the crystal symmetry lowers to a chiral monoclinic space group, explaining the asymmetry in the chiral spin order, and establishing a mechanism by which the spin chirality could reverse via magnetostructural coupling. The reversal of spin chirality in the absence of any externally applied field would substantially broaden the use of chiral magnets for applications in spintronic devices. In this manuscript the authors demonstrate the spontaneous reversal of spin chirality in the topological magnet EuAl4 using resonant elastic x-ray scattering. [ABSTRACT FROM AUTHOR]

Materials exhibiting a spontaneous reversal of spin chirality have the potential to drive the widespread adoption of chiral magnets in spintronic devices. Unlike the majority of chiral magnets that require the application of an external field to reverse the spin chirality, we observe the spin chirality to spontaneously reverse in the topological magnet EuAl4. Using resonant elastic x-ray scattering we demonstrate that all four magnetic phases in EuAl4 are single-k, where the first two magnetic phases are characterized by spin density wave order and the last two by helical spin order. A single spin chirality was stabilised across the 1mm2 sample, and the reversal of spin chirality occurred whilst maintaining a helical magnetic structure. At the onset of the helical magnetism, the crystal symmetry lowers to a chiral monoclinic space group, explaining the asymmetry in the chiral spin order, and establishing a mechanism by which the spin chirality could reverse via magnetostructural coupling. The reversal of spin chirality in the absence of any externally applied field would substantially broaden the use of chiral magnets for applications in spintronic devices. In this manuscript the authors demonstrate the spontaneous reversal of spin chirality in the topological magnet EuAl4 using resonant elastic x-ray scattering. [ABSTRACT FROM AUTHOR]

Local symmetry of crystal field is crucial for optical temperature sensitivity that based on the thermal couple levels of rare earth ions. In this work, Lu3+ ions were introduced to alter the local environment of Er3+ ions in oxyfluoride glass-ceramics. X-ray diffraction patterns and transmission electron microscope images show that Y 5 O 4 F 7 nanocrystals are precipitated in glass-ceramics. Incorporation of rare-earth ions into the Y 5 O 4 F 7 nanocrystals is confirmed by absorption and electron energy loss spectra. The Judd-Ofelt (J-O) theory analysis reveals that local symmetry of the crystal field around Er3+ decreasing due to Lu3+ co-doping. Temperature sensing property of the Y 5 O 4 F 7 : Er3+/Yb3+/Lu3+ nanocrystal incorporated glass-ceramic was investigated, and the optimal relative temperature sensitivity S R reaches 1.50 % K−1 in 0.25 mol.% Lu3+ doped specimen. Results show that the moderate addition of Lu3+ can improve the temperature sensitivity of glass-ceramic containing Y 5 O 4 F 7 :Er3+/Yb3+ nanocrystals, which provide a promising avenue for optical temperature sensing. [ABSTRACT FROM AUTHOR]

Higher-order topological phases in non-Hermitian photonics revolutionize the understanding of wave propagation and modulation, which lead to hierarchical states in open systems. However, intrinsic insulating properties endorsed by the lattice symmetry of photonic crystals fundamentally confine the robust transport only at explicit system boundaries, letting alone the flexible reconfiguration in hierarchical states at arbitrary positions. Here, we report a dynamic topological platform for creating the reconfigurable hierarchical bound states in heat transport systems and observe the robust and nonlocalized higher-order states in both the real-and imaginary-valued bands. Our experiments showcase that the hierarchical features of zero-dimension corner and nontrivial edge modes occur at tailored positions within the system bulk states instead of the explicit system boundaries. Our findings uncover the mechanism of non-localized hierarchical non-trivial topological states and offer distinct paradigms for diffusive transport field management. [ABSTRACT FROM AUTHOR]

Herein, lead‐free, mixed‐halide perovskites of cesium bismuth bromide/iodide are synthesized by a hydrothermal method, and their structures and optical properties of the solid solution compounds are examined. The synthesized compounds exhibit X‐ray diffraction patterns similar to that of trigonal Cs3Bi2Br9 (CBB), whose reflections are shifted to lower angles depending on the experimental iodine content. Very interestingly, even with the excessive introduction of iodine content in nominal, the symmetry of the crystals is kept to be trigonal, indicating that bromide CBB and iodide Cs3Bi2I9 (CBI) are crystallographically mixed in a facile way, although the stable crystal form of CBI is hexagonal. The optical properties of bandgap energy Eg and photoluminescence (PL) for the synthesized crystals are also examined. It is found that Eg decreases and PL peak position is correspondingly shifted to a longer wavelength with an increase in the experimental iodine content due to their band‐to‐band transitions. Moreover, first‐principles calculation suggests the reduction of Eg with iodine content and the varied nature of band structure from direct (trigonal CBB) to indirect (trigonal CBI) transition. These novel findings can make the proposed strategy successful for developing lead‐free, mixed‐halide Bi‐based perovskite crystals with the tunability of their optical properties. [ABSTRACT FROM AUTHOR]

The free-field switching of the perpendicular magnetization by the out-of-plane polarized spin current induced spin-orbit torque makes it a promising technology for developing high-density memory and logic devices. The materials intrinsically with low symmetry are generally utilized to generate the spin current with out-of-plane spin polarization. However, the generation of the out-of-plane polarized spin current by engineering the symmetry of materials has not yet been reported. Here, we demonstrate that paramagnetic CaRuO3 films are able to generate out-of-plane polarized spin current by engineering the crystal symmetry. The non-uniform oxygen octahedral tilt/rotation along film's normal direction induced by oxygen octahedral coupling near interface breaks the screw-axis and glide-plane symmetries, which gives rise to a significant out-of-plane polarized spin current. This spin current can drive field-free spin-orbit torque switching of perpendicular magnetization with high efficiency. Our results offer a promising strategy based on crystal symmetry design to manipulate spin current and could have potential applications in advanced spintronic devices. The authors realize generation of out-of-plane polarized spin current in perovskite oxide CaRuO3 with reduced crystal symmetry by engineering the oxygen octahedra, which can drive efficient field-free switching of perpendicular magnetization. [ABSTRACT FROM AUTHOR]