ABSTRACT Inorganic antiperovskites with the formula X 3 A N ( X = Ba, Sr, Ca, Mg; A = As, Sb) have recently been reported to exhibit excellent optoelectronic properties including small carrier effective masses, suitable direct bandgaps, high optical absorption coefficients as well as allowed optical transitions at the band edges. Using the ammonothermal method, we have synthesized the imide antiperovskites AE 5 Pn 2 (NH) 2 ( AE = Ca, Sr; Pn = As, Sb, Bi). The crystal structures of AE 5 Pn 2 (NH) 2 were solved and refined in the orthorhombic space group Pbam by single‐crystal x‐ray diffraction (scXRD), and further confirmed using powder X‐ray diffraction (pXRD) and Raman spectroscopy. Depending on the ion size ratio between AE 2+ and Pn 3– , different degrees of octahedral tilting can be observed. Soft X‐ray spectroscopy was used to study the band gap and electronic structure, and revealed the presence of oxygen impurities. The AE 5 Pn 2 (NH) 2 compounds can further react to form the ternary antiperovskites AE 3 Pn N. Density functional theory calculations reveal favorable transport and optical properties. Narrow direct band gaps in the range of 0.87–1.76 eV could be verified experimentally, making AE 5 Pn 2 (NH) 2 not only suitable as precursor materials for the corresponding AE 3 Pn N antiperovskites, but also as promising candidates for solar cell absorber materials.

Chiral crystals have a noncentrosymmetric unit cell and can manifest spin-orbit coupling (SOC)-induced band splitting, even in the absence of an atomic magnetic moment. We examine the particular case of Strukturbericht B20 compounds, with AlPt as representative material, by means of first-principles electronic structure calculations. We show how nonzero, but punctually compensated k textures for both the spin and the orbital magnetic moment, emerge as a function of the lattice geometry, SOC, and in dependence on finite temperature. An applied electric field perturbation is shown to set up a bulk Edelstein effect in terms of both spin and orbital magnetic moment.

We present an approach for first principles investigations on the spin driven electric polarization in type II multiferroics. We propose a parametrization of the polarization with the parameters calculated using the Korringa-Kohn-Rostoker Green function (KKR-GF) formalism. Within this approach the induced electric polarization of a unit cell is represented in terms of three-site parameters. Those antisymmetric with respect to spin permutation are seen as an ab-initio based counter-part to the phenomenological parameters used within the inverse-Dzyaloshinskii-Moriya-interaction (DMI) model. Due to their relativistic origin, these parameters are responsible for the electric polarization induced in the presence of a non-collinear spin alignment in materials with a centrosymmetric crystal structure. Beyond to this, our approach gives direct access to the element- or site-resolved electric polarization. To demonstrate the capability of the approach, we consider several examples of the so-called type II multiferroics, for which the magneto-electric effect is observed either as a consequence of an applied magnetic field (we use Cr_2O_3 as a prototype), or as a result of a phase transition to a spin-spiral magnetic state, as for instance in MnI_2, CuCrO_2 and AgCrO_2.

Two-dimensional perovskites show intriguing optoelectronic properties due to their anisotropic structure and multiple quantum well structure. Here, we report the first three gold-based Ruddlesden-Popper type two-dimensional double perovskites with a general formula (NOP)4AuIBIIII8 (B = Au, Bi, Sb) employing naphthalene-O-propylammonium (NOP) as an organic cation. They were found to form highly crystalline thin films on various substrates, predominantly oriented in the [001] direction featuring continuous, crack-free film areas on the μm2 scale. The thin films show strong optical absorption in the visible region, with band gap energies between 1.48 and 2.32 eV. Density functional theory calculations support the experimentally obtained band gap energies and predict high charge-carrier mobilities and effective charge separation. A comprehensive study with time-resolved microwave conductivity (TRMC) and optical-pump-THz-probe (OPTP) spectroscopy revealed high charge-carrier mobilities for lead-free two-dimensional perovskites of 4.0 ± 0.2 cm2(V s)-1 and charge-carrier lifetimes in the range of μs. Photoconductivity measurements under 1 sun illumination demonstrated the material's application as a photodetector, showing a 2-fold increase in conductivity when exposed to light.

Layered 2D van der Waals materials, such as transition metal dichalcogenides, are promising for nanoscale spintronic and optoelectronic applications. Harnessing their full potential requires understanding both intrinsic transport and the dynamics of optically excited spin and charge carriers, particularly the transition between excited spin polarization and the conduction band's intrinsic spin texture. Here, we investigate the spin polarization of the conduction bands of bulk WSe_{2} using static and time-resolved spin-resolved photoemission spectroscopy, complemented by photocurrent calculations. Electron doping reveals the intrinsic spin polarization, while time-resolved measurements trace the evolution of excited spin carriers. We find that intervalley scattering is spin-conserving, with spin transport initially governed by photoexcited carriers and aligning with the intrinsic conduction band spin polarization after ∼150  fs.

Chirality is an inherent characteristics of some objects in nature. In magnetism chiral magnetic textures can be formed in systems with broken inversion symmetry and due to an antisymmetric magnetic interaction, known as Dzyaloshinskii--Moriya interaction (DMI). Here, aiming on a fundamental understanding of this chiral interaction on the atomic scale, we design several synthetic layered structures composed of alternating atomic layers of 3d ferromagnetic metals epitaxially grown on Ir(001). We demonstrate both experimentally and theoretically that the atomistic DMI depends critically not only on the orbital occupancy of the interface magnetic layer but also on the sequence of the atomic layers. The effect is attributed to the complexity of the electronic structure and the contribution of different orbitals to the hybridization and DMI. We anticipate that our results provide guidelines for controlling both the chirality and the magnitude of the atomistic DMI.

Induced by an ultra-short laser pulse, the electronic structure of a material undergoes strong modifications leading to a fast demagnetization in magnetic materials. Induced spin-flip transitions are one of the reasons for demagnetization, that is associated in the literature with a Stoner-like mechanism. On the other hand, demagnetization due to transverse spin fluctuations is usually discussed on the basis of the Heisenberg Hamiltonian and hardly accounts for the modification of the electronic structure. In this work we demonstrate a strong impact of the laser-induced electron transitions, both spin-flip and spin-conserving, on the exchange coupling parameters. For this, a simple two-step scheme is suggested. As a first step, the electronic structure time evolution during the ultra-short laser pulse is described accurately within time-dependent density-functional theory calculations. As a next step, the information on the time-dependent electronic structure is used for calculations of the parameters of the Heisenberg Hamiltonian. A strong modification of the exchange coupling parameters is found on the femtosecond time scale as a consequence of the depopulation of the electronic states in response to the applied ultra-short laser pulse. Due to the relatively slow attenuation of these changes after the laser pulse, taking place on the subpicosecond/picosecond time scale, we expect an appreciable impact on the magnon energies and that way on the demagnetization/relaxation processes. The same concerns the spin-lattice interactions playing a central role for the relaxation process. A strong impact of the laser-induced modification of the electronic structure on the spin-lattice coupling parameters is also shown in this work.

An abundance of oxide, halide and chalcogenide perovskites have been explored, demonstrating outstanding properties, while the emerging nitride perovskites are extremely rare due to their challenging synthesis requirements. By inverting the ion type in the perovskite structure, the corresponding antiperovskite structure is obtained. Among them, ternary antiperovskite nitrides X3AN (X=Ba, Sr, Ca, Mg; A=As, Sb) have recently been identified as exhibiting excellent optoelectronic properties. To explore the unrealized composition space of nitride perovskites, the ammonothermal method was applied, yielding three new layered quaternary imide-based defect-antiperovskites, namely AE5AsPn(NH)2 (AE=Ca, Sr; Pn=Sb, Bi). These new compounds feature distorted square-pyramidal coordination around the imide-group (Ca5NH). Layers with Ca2+ vacancies are found with an alternating As3- and Pn3- (Pn3-=Sb3-, Bi3-) coordination along the A-site, forming a two-dimensional (2D) structure. All three AE5AsPn(NH)2 compounds show suitable direct band gaps within the visible light spectrum. Density functional theory calculations reveal favorable band dispersion, as well as transport and optical properties, especially along the out-of-plane direction, demonstrating their 3D character of electronic transport. The narrow tunable direct band gaps and favorable charge carrier properties make AE5AsPn(NH)2 promising candidates for solar cell absorber materials.

Exploring new strategies to manipulate the order parameter of magnetic materials by electrical means is of great importance not only for advancing our understanding of fundamental magnetism but also for unlocking potential applications. A well-established concept uses gate voltages to control magnetic properties by modulating the carrier population in a capacitor structure1-5. Here we show that, in Pt/Al/Fe/GaAs(001) multilayers, the application of an in-plane charge current in Pt leads to a shift in the ferromagnetic resonance field depending on the microwave frequency when the Fe film is sufficiently thin. The experimental observation is interpreted as a current-induced modification of the magnetocrystalline anisotropy ΔHA of Fe. We show that (1) ΔHA decreases with increasing Fe film thickness and is connected to the damping-like torque; and (2) ΔHA depends not only on the polarity of charge current but also on the magnetization direction, that is, ΔHA has an opposite sign when the magnetization direction is reversed. The symmetry of the modification is consistent with a current-induced spin6-8 and/or orbit9-13 accumulation, which, respectively, act on the spin and/or orbit component of the magnetization. In this study, as Pt is regarded as a typical spin current source6,14, the spin current can play a dominant part. The control of magnetism by a spin current results from the modified exchange splitting of the majority and minority spin bands, providing functionality that was previously unknown and could be useful in advanced spintronic devices.

This study reports the synthesis and crystal structure determination of a novel CrTe3 phase using various experimental and theoretical methods. The average stoichiometry and local phase separation of this quenched high-pressure phase were characterized by ex situ synchrotron powder X-ray diffraction and total scattering. Several structural models were obtained using simulated annealing, but all suffered from an imperfect Rietveld refinement, especially at higher diffraction angles. Finally, a novel stoichiometrically correct crystal structure model was proposed on the basis of electron diffraction data and refined against powder diffraction data using the Rietveld method. Scanning electron microscopy-energy-dispersive X-ray spectrometry (EDX) measurements verified the targeted 1:3 (Cr:Te) average stoichiometry for the starting compound and for the quenched high-pressure phase within experimental errors. Scanning transmission electron microscopy (STEM)-EDX was used to examine minute variations of the Cr-to-Te ratio at the nanoscale. Precession electron diffraction (PED) experiments were applied for the nanoscale structure analysis of the quenched high-pressure phase. The proposed monoclinic model from PED experiments provided an improved fit to the X-ray patterns, especially after introducing atomic anisotropic displacement parameters and partial occupancy of Cr atoms. Atomic resolution STEM and simulations were conducted to identify variations in the Cr-atom site-occupancy factor. No significant variations were observed experimentally for several zone axes. The magnetic properties of the novel CrTe3 phase were investigated through temperature- and field-dependent magnetization measurements. In order to understand these properties, auxiliary theoretical investigations have been performed by first-principles electronic structure calculations and Monte Carlo simulations. The obtained results allow the observed magnetization behavior to be interpreted as the consequence of competition between the applied magnetic field and the Cr-Cr exchange interactions, leading to a decrease of the magnetization towards T = 0 K typical for antiferromagnetic systems, as well as a field-induced enhanced magnetization around the critical temperature due to the high magnetic susceptibility in this region.

Owing to their exceptional mechanical, electronic, and phononic transport properties, compositionally complex alloys, including high-entropy alloys, represent an important class of materials. However, the interplay between chemical disorder and electronic correlations, and its influence on electronic structure-derived properties, remains largely unexplored. This is addressed for the archetypal CrMnFeCoNi alloy using resonant and valence band photoemission spectroscopy, electrical resistivity, and optical conductivity measurements, complemented by linear response calculations based on density functional theory. Utilizing dynamical mean-field theory, correlation signatures and damping in the spectra are identified, highlighting the significance of many-body effects, particularly in states distant from the Fermi edge. Electronic transport remains dominated by disorder and potentially short-range order, especially at low temperatures, while visible-spectrum optical conductivity and high-temperature transport are influenced by short quasiparticle lifetimes. These findings improve our understanding of element-specific electronic correlations in compositionally complex alloys and facilitate the development of advanced materials with tailored electronic properties.

Exploring novel strategies to manipulate the order parameter of magnetic materials by electrical means is of great importance, not only for advancing our understanding of fundamental magnetism, but also for unlocking potential practical applications. A well-established concept to date uses gate voltages to control magnetic properties, such as saturation magnetization, magnetic anisotropies, coercive field, Curie temperature and Gilbert damping, by modulating the charge carrier population within a capacitor structure. Note that the induced carriers are non-spin-polarized, so the control via the electric-field is independent of the direction of the magnetization. Here, we show that the magnetocrystalline anisotropy (MCA) of ultrathin Fe films can be reversibly modified by a spin current generated in Pt by the spin Hall effect. The effect decreases with increasing Fe thickness, indicating that the origin of the modification can be traced back to the interface. Uniquely, the change in MCA due to the spin current depends not only on the polarity of the charge current but also on the direction of magnetization, i.e. the change in MCA has opposite sign when the direction of magnetization is reversed. The control of magnetism by the spin current results from the modified exchange splitting of majority- and minority-spin bands, and differs significantly from the manipulation by gate voltages via a capacitor structure, providing a functionality that was previously unavailable and could be useful in advanced spintronic devices.

Spin-orbit interaction affects the band structure of topological insulators beyond the opening of an inverted gap in the bulk bands, and the understanding of its effects on the surface states is of primary importance to access the underlying physics of these exotic states. Here, we propose an $\textit{ab initio}$ approach benchmarked by pump-probe angle-resolved photoelectron spectroscopy data to model the effect of spin-orbit coupling on the surface states of a topological insulator. The critical novelty of our approach lies in the possibility of accounting for a partial transfer of the spin-orbit coupling to the surface states, mediated by the hybridization with the surface resonance states. In topological insulators, the fraction of transferred spin-orbit coupling influences the strength of the hexagonal warping of the surface states, which we use as a telltale of the capability of our model to reproduce the experimental dispersion. The comparison between calculations and measurements, of both the unoccupied and part of the occupied Dirac cone, indicates that the fraction of spin-orbit coupling transferred to the surface states by hybridization with the resonance states is between 70% and 85% of its full atomic value. This offers a valuable insight to improve the modeling of surface state properties in topological insulators for both scientific purposes and technological applications.

Kubo's linear response formalism has been used to calculate the orbital Hall conductivity (OHC) for nonmagnetic undoped and doped transition metal systems, focusing on the impact of different types of disorder and the role of vertex corrections for the OHC. The doping and temperature dependence of the OH conductivity have been investigated and compared with corresponding results for the spin Hall conductivity (SHC). A strong difference has been found between the results for undoped and doped metallic systems. For elemental systems at finite temperature, a dominating role of the intrinsic contribution to the temperature-dependent OH and SH conductivities is found. Moreover, the different temperature-dependent behavior of the intrinsic SOC-independent OHC and SOC-driven SHC indicates a nontrivial relationship between these quantities. It is shown that, in contrast to the intrinsic part of the OH and SH conductivities, the extrinsic contributions in doped systems are determined by spin-orbit coupling for both of them. This effect is dominating at low temperature, strongly decreasing at higher temperatures owing to the increasing impact of the electron-phonon scattering.

The possibility to combine organic semiconducting materials with inorganic halide perovskites opens exciting pathways toward tuning optoelectronic properties. Exploring stable and nontoxic, double perovskites as a host for electroactive organic cations to form two-dimensional (2D) hybrid materials is an emerging opportunity to create both functional and lead-free materials for optoelectronic applications. By introducing naphthalene and pyrene moieties into Ag-Bi-I and Cu-Bi-I double perovskite lattices, intrinsic electronic challenges of double perovskites are addressed and the electronic anisotropy of 2D perovskites can be modulated. (POE)4AgBiI8 containing pyrene moieties in the 2D layers was selected from a total of eight new 2D double perovskites, exhibiting a favorable electronic band structure with a type IIb multiple quantum well system based on a layer architecture suitable for out-of-plane conductivity and leading to a photocurrent response ratio of almost 3 orders of magnitude under AM1.5G illumination. Finally, an exclusively parallelly oriented thin film of (POE)4AgBiI8 was integrated into a device to construct the first pure n = 1 Ruddlesden-Popper 2D double perovskite solar cell.

Christian Lidig,1 Jan Minár,2 Jürgen Braun,3 Hubert Ebert,3 Andrei Gloskovskii,4 Jonas A. Krieger,5,6 Vladimir Strocov,5 Mathias Kläui,1 and Martin Jourdan1 1Institut für Physik, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany 2New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen, Czech Republic 3Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 11, 81377 München, Germany 4Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany 5Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland 6Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich, Switzerland

2D hybrid organic and inorganic perovskites (HOIPs) are used as capping layers on top of 3D perovskites to enhance their stability while maintaining the desired power conversion efficiency (PCE). Therefore, the 2D HOIP needs to withstand mechanical stresses and deformations, making the stiffness an important observable. However, there is no model for unravelling the relationship between their crystal structures and mechanical properties. In this work, explainable machine learning (ML) models are used to accelerate the in silico prediction of mechanical properties of 2D HOIPs, as indicated by their out-of-plane and in-plane Young's modulus. The ML models can distinguish between stiff and non-stiff 2D HOIPs, and extract the dominant physical feature influencing their Young's moduli, viz. the metal-halogen-metal bond angle. Furthermore, the steric effect index (STEI) of cations is found to be a rough criterion for non-stiffness. Their optimal ranges are extracted from a probability analysis. Based on the strong correlation between the deformation of octahedra and the Young's modulus, the transferability of the approach from single-layer to multi-layer 2D HOIPs is demonstrated. This work represents a step toward unravelling the complex relationship between crystal structure and mechanical properties of 2D HOIPs using ML as a tool. Explainable machine learning is applied to study the mechanical properties of n = 1 2D hybrid halide perovskites via Feature Engineering, the significant features influencing the structural non-stiffness are extracted. The transferability of the ML model from single-layer to multi-layer 2D hybrid halide perovskites is achieved. image

The thermoelectric performance of existing perovskites lags far behind that of state-of-the-art thermoelectric materials such as SnSe. Despite halide perovskites showing promising thermoelectric properties, namely, high Seebeck coefficients and ultralow thermal conductivities, their thermoelectric performance is significantly restricted by low electrical conductivities. Here, we explore new multi-anion antiperovskites X6NFSn2 (X = Ca, Sr, and Ba) via B-site anion mutation in antiperovskite and global structure searches and demonstrate their phase stability by first-principles calculations. Ca6NFSn2 and Sr6NFSn2 exhibit decent Seebeck coefficients and ultralow lattice thermal conductivities (<1 W m(-1) K-1). Notably, Ca6NFSn2 and Sr6NFSn2 show remarkably larger electrical conductivities compared to the halide perovskite CsSnI3. The combined superior electrical and thermal properties of Ca6NFSn2 and Sr6NFSn2 lead to high thermoelectric figures of merit (ZTs) of -1.9 and -2.3 high temperatures. Our exploration of multi-anion antiperovskites X6NFSn2 (X = Ca, Sr) realizes the "phonon-glass, electron-crystal"concept within the antiperovskite structure.

InBi(0 01) is formed epitaxially on InAs(1 1 1)-A by depositing Bi onto an In-rich surface. Angle-resolved photoemission measurements reveal topological electronic surface states, close to the M high symmetry point. This demonstrates a heteroepitaxial system entirely in the III-V family with topological electronic properties. InBi shows coexistence of Bi and In surface terminations, in contradiction with other III-V materials. For the Bi termination, the study gives a consistent physical picture of the topological surface electronic structure of InBi(0 0 1) terminated by a Bi bilayer rather than a surface formed by splitting to a Bi monolayer termination. Theoretical calculations based on relativistic density functional theory and the one-step model of photoemission clarify the relationship between the InBi(0 01) surface termination and the topological surface states, supporting a predominant role of the Bi bilayer termination. Furthermore, a tight-binding model based on this Bi bilayer termination with only Bi-Bi hopping terms, and no Bi-In interaction, gives a deeper insight into the spin texture.

Recently, the interplay between spin and lattice degrees of freedom has gained a lot of attention due to its importance for various fundamental phenomena as well as for spintronic and magnonic applications. Examples are ultrafast angular momentum transfer between the spin and lattice subsystems during ultrafast demagnetization, frustration driven by structural distortions in transition metal oxides, or in acoustically driven spin-wave resonances. In this work, we provide a systematic analysis of spin-lattice interactions for ferro- and antiferromagnetic materials and focus on the role of lattice symmetries and dimensions, magnetic order, and the relevance of spin-lattice interactions for angular momentum transfer as well as magnetic frustration. For this purpose, we use a recently developed scheme which allows an efficient calculation of spin-lattice interaction tensors from first principles. In addition to that, we provide a more accurate and self consistent scheme to calculate ab initio spin lattice interactions by using embedded clusters which allows to benchmark the performance of the scheme introduced previously.