The topological Hall effect (THE) arises from a Berry phase imprinted on conduction electron spins as they traverse noncollinear magnetic textures. It constitutes a transport hallmark of chiral magnetism. Very large THE signals are theoretically expected in oxide heterostructures combining 3d or 4d ferromagnets and 5d metals with strong spin–orbit coupling. However, experimental realizations have so far yielded only modest signals whose emergence could not be linked to any chiral magnetic texture. Using ultrathin La₀.₇Sr₀.₃MnO₃/SrIrO₃ bilayers, here we demonstrate a THE that can be switched ON and OFF by the magnetic history, and we establish a direct one-to-one correspondence between the transport anomaly and the emergence—or disappearance—of a chiral magnetic texture at the interface. Further, the associated THE signal is giant, reaching values an order of magnitude larger than observed earlier in analogous systems. Beyond providing a rare, unequivocal evidence for a pure THE, the controllable link between magnetic chirality and the giant Hall signal at oxide interfaces shows a path for engineering reconfigurable conspicuous topological responses, which could impact spintronic sensing and beyond. The topological Hall effect is a key transport signature of chiral magnetism, yet experimental realizations in oxide heterostructures have been limited. Here, the authors use ultrathin La₀.₇Sr₀.₃MnO₃/SrIrO₃ bilayers to demonstrate a switchable, giant topological Hall effect linked to chiral magnetic textures, paving the way for advanced spintronic applications

The unique coupling between magnetic order and photo-generated excitons, electron-hole pairs bound by Coulomb interaction, in layered magnetic semiconductors offers a powerful mechanism for controlling light-matter interactions. In the van der Waals antiferromagnet CrSBr, this coupling is exceptionally strong and manifests distinctly between two coexisting excitonic states: the localised, Frenkel-like XA exciton and the more delocalised, Wannier-Mott-like XB exciton, providing a unique playground for the optical control of magnetism. Here, we reveal how chlorine incorporation reshapes the magneto-optical interplay in CrSBr1-xClx by simultaneously modifying its electronic structure, excitonic properties, and magnetic interactions. Combining magneto-optical spectroscopy up to 85 T with state-of-the-art quasiparticle self-consistent GW (QSGW) calculations on alloy supercells, we show that Cl insertion progressively localises the excitonic wavefunctions and drives both states toward a more Frenkel-like regime. This evolution is accompanied by a systematic reduction of the magnetic-field-induced energy renormalisation, most prominently for the XB exciton. Our work connects exciton character directly to magneto-excitonic coupling. Furthermore, it establishes compositional alloying as an effective strategy for engineering the coupling between magnetic and optical properties in van der Waals magnetic semiconductors.

The recent realization of freestanding membranes of perovskite oxides has enabled their deterministic mechanical assembly into twisted homo bilayers. Twisted oxide interfaces feature a non-homogeneous pattern of shear strains determined by the atomic registry through the strong ionic-covalent bonding of this family of compounds. Twisted ferroelectrics open an unprecedented opportunity to tailor topological polar landscapes in a way determined by the flexoelectric coupling of polarization to the large strain gradients developing with the modulation of the moiré coincidence pattern. Yet, flexoelectricity is a universal phenomenon which may render polar landscapes in non-ferroelectric materials. Here we report a polar topology in twisted membranes of SrTiO3 (STO), a paraelectric centrosymmetric compound. The polar landscape is generated by the flexoelectrically induced polarization driven by the strain modulation triggered by twisting, as also supported by machine-learned force fields based on first-principles calculations. We further show that the strain and polarization patterns in top and bottom layers are correlated in a way which breaks inversion and mirror symmetries as dictated by the emergent chirality imposed by twisting. This finding opens exciting opportunities for the exploration of novel physical effects and functionalities.

PdSb _2 is a metal in which band structure calculations suggest the presence of sixfold-degenerate fermions. Surface bands emerging from the sixfold-degenerate point may exhibit nontrivial topological properties. Here, we present Scanning Tunneling Microscopy (STM) measurements of PdSb _2 between 4.2 and 60 K and under magnetic fields up to 14 T. We identify a gap-like feature with a width of approximately 20 meV around the Fermi level. We additionally provide Density Functional Theory (DFT) calculations and discuss the possible connection between the observed tunneling conductance and the surface band structure. We find a small incomplete gap-like feature in the density of states which has a similar size as the feature observed in the experiment but is located slightly above the Fermi level. We furthermore estimate surface relaxation of atomic positions and find that Sb suffers larger relaxations than Pd atoms. This could influence the position in energy of the features found in the band structure. Our measurements show that PdSb _2 is a good metal, with a density of states which presents, however, interesting features close to the Fermi level.

Freestanding ferroelectric oxides integrated with 2D semiconductors offer a platform for reconfigurable electronic functionalities beyond conventional dielectric gating. However, once released from epitaxial constraint and transferred directly onto metallic gates, the BaTiO3 (BTO) membranes under study preferentially adopt an in-plane polarization configuration, suppressing out-of-plane ferroelectric coupling at room temperature. Here, we demonstrate that single-layer MoS2 field-effect transistors gated by 25 nm freestanding BTO exhibit excellent electrostatic control at room temperature, with subthreshold swings down to 85 mV dec- 1 and high on/off ratios, yet negligible hysteresis, highlighting the effectiveness of depolarized BTO as an ultrahigh-κ dielectric. Upon cooling, robust counter-clockwise ferroelectric hysteresis emerges, with memory windows of ∼0.4 V, stable over 500 cycles and retention times exceeding 105 s. Temperature-dependent x-ray diffraction reveals structural signatures consistent with the bulk phase transitions sequence of BTO and confirms a predominant in-plane lattice orientation near room temperature. The combined electrical and structural analysis indicates that phase-dependent polarization anisotropy, together with domain-wall dynamics and interfacial screening processes, stabilizes an out-of-plane polarization component at low temperature in the rhombohedral and orthorhombic phases.

Functionalization of transition metal dichalcogenides is a key process for future technological applications. To date, various routes, primarily chemical, have been proposed for efficient functionalization with thiol moieties. Previous functionalization protocols have generally taken advantage of intrinsic defects typically present on the surface. However, the specific nature of the molecule-substrate bond, covalent or noncovalent, has always remained controversial. In this work, we present a study of the functionalization of MoS2 by physical vapor deposition in ultrahigh vacuum conditions of the 4-aminothiophenol molecule. We have investigated its interaction with the intrinsic sulfur vacancies present in MoS2 and with additional vacancies generated by ion bombardment. We observe that the molecule is found in planar configuration on the surface and the thiol moiety remains intact. Atomic force microscopy measurements show high diffusion of molecules through the surface, along with a strong interaction between the thiol moieties and the tip itself. Interestingly, this interaction leads to a contrast inversion in the acquired AFM images, which is a key observation that leads to consider that molecules are not covalently bonded. Density functional theory calculations rule out thiol dehydrogenation, attributing the observed contrast inversion to molecular tip functionalization. These findings provide compelling evidence of a nonspecific physisorption interaction, confirming the absence of covalent bonding between the molecule and the surface.

Hexagonal boron nitride (h-BN) is a key material for 2D heterostructures and electronic devices. It has been widely employed as encapsulant, dielectric barrier and, mainly, as a substrate for graphene since it significantly enhances its electronic properties and in particular the mobility of the charge carriers. However, these advances are to a great extent restricted to laboratory-scale experiments due to the limited scalability of current h-BN growth methods. In this work, we present an in-depth study of h-BN thin films grown by ion beam assisted deposition (IBAD), a versatile and scalable technique that enables the synthesis of high-quality ultra-flat layers with tunable thickness on metallic, semiconducting, or insulating substrates. Comprehensive structural, optical, and morphological characterization of the h-BN films was performed using complementary spectroscopic and advanced microscopy techniques. Our results reveal the growth of highly in-plane textured nanocrystalline h-BN layers exhibiting very low defect density and ultraflat surfaces with a wide bandgap around 5.35 eV. These findings make IBAD a promising method for the scalable growth of highly performing h-BN thin films for integration as substrates in graphene-based devices.

ABSTRACT Freestanding ferroelectric oxides integrated with 2D semiconductors offer a platform for reconfigurable electronic functionalities beyond conventional dielectric gating. However, once released from epitaxial constraint and transferred directly onto metallic gates, the BaTiO 3 (BTO) membranes under study preferentially adopt an in‐plane polarization configuration, suppressing out‐of‐plane ferroelectric coupling at room temperature. Here, we demonstrate that single‐layer MoS 2 field‐effect transistors gated by 25 nm freestanding BTO exhibit excellent electrostatic control at room temperature, with subthreshold swings down to 85 mV dec − 1 and high on/off ratios, yet negligible hysteresis, highlighting the effectiveness of depolarized BTO as an ultrahigh‐κ dielectric. Upon cooling, robust counter‐clockwise ferroelectric hysteresis emerges, with memory windows of ∼0.4 V, stable over 500 cycles and retention times exceeding 10 5 s. Temperature‐dependent x‐ray diffraction reveals structural signatures consistent with the bulk phase transitions sequence of BTO and confirms a predominant in‐plane lattice orientation near room temperature. The combined electrical and structural analysis indicates that phase‐dependent polarization anisotropy, together with domain‐wall dynamics and interfacial screening processes, stabilizes an out‐of‐plane polarization component at low temperature in the rhombohedral and orthorhombic phases.

ABSTRACT The increase in demand for advanced electronic components, especially for the new information technologies, calls for an expansion of the materials portfolio and devices. The integration of freestanding transition metal oxide (TMO) membranes with two‐dimensional van der Waals (2DvdW) materials presents a unique opportunity to explore novel interfacial phenomena, driven by their diverse crystal symmetries, bonding characteristics, and electronic correlations. These interactions can lead to the emergence of moiré periodicities, which fundamentally alter the physical properties of the hybrid systems. The interplay of differing symmetries and structural distortions in TMOs and ultrathin 2DvdW materials complicates the prediction of their collective behavior. The twisting of cubic and hexagonal lattices creates complex moiré patterns, while variations in energy scales and correlation strengths further enhance this complexity. Understanding the evolution of moiré periodicity in relation to symmetry and distortion is crucial but remains a significant experimental and theoretical challenge. This perspective explores the integration of 2D van der Waals layers with twisted transition metal oxide (TMO) membranes. We discuss key challenges for both material classes, emphasizing how symmetry, lattice distortions, and electronic correlations govern their structural and electronic behavior. We also examine limitations of current theoretical approaches and argue for the need to develop better multiscale computational methods to model and design these hybrid systems.

Epitaxial interfaces combining 3d and 5d transition metal oxides are a fertile playground to examine the interplay between topology and electron correlations. In this paper, we explore magnetism and transport of bilayers combining ferromagnetic La0.7Sr0.3MnO3 and the strong spin-orbit coupling material SrIrO3. We have found an interfacial magnetic proximity effect driving an intrinsic contribution to the anomalous Hall effect of topological origin. The interfacial proximity interaction is enabled by the Mn-O-Ir bonding reconstruction and depends on layer sequence. While bilayers with the La0.7Sr0.3MnO3 on top featuring a robust Mn magnetism at the interface show the intrinsic AHE contribution, it is absent in bilayers with the inverted layer sequence (SrIrO3 layer on top) showing strongly suppressed magnetism at the interface. These results illustrate the leading role of interfacial atomic reconstructions on the interplay between topology and correlations at 3d/5d oxide interfaces. This finding may be of interest in future oxide topological spintronics and spin-orbitronics.

Tailoring magnetoresistance and magnetic anisotropy in van der Waals magnetic materials is essential for advancing their integration into technological applications. In this regard, strain engineering has emerged as a powerful and versatile strategy to control magnetism at the 2D limit. Here, it is demonstrated that compressive biaxial strain significantly enhances the magnetoresistance and magnetic anisotropy of few-layer CrSBr flakes. Strain is efficiently transferred to the flakes from the thermal compression of a polymeric substrate upon cooling, as confirmed by temperature-dependent Raman spectroscopy. This strain induces a remarkable increase in the magnetoresistance ratio and in the saturation fields required to align the magnetization of CrSBr along each of its three crystalographic directions, reaching a twofold enhancement along the magnetic easy axis. This enhancement is accompanied by a subtle reduction of the Néel temperature by ≈10 K. The experimental results are fully supported by first-principles calculations, which link the observed effects to a strain-driven modification in interlayer exchange coupling and magnetic anisotropy energy. These findings establish strain engineering as a key tool for fine-tuning magnetotransport properties in 2D magnetic semiconductors, paving the way for implementation in spintronics and information storage devices.

Since the discovery of graphene in 2004, there has been rapid progress in research on two-dimensional (2D) material’s potential applications with significant impact. Efforts to bring 2D materials closer to industrial production, quality assessment, and standardization still need to be expanded upon. This remains challenging because sophisticated analytics techniques are required to analyze a limited amount of material with high variability due to differences in the synthesis process and the lack of a clear standard for comparing results. Modern methods can evaluate domain size, surface coverage, defects, dopants, mobility, and photoluminescence parameters. Still, it is challenging to understand the structure–property relationship due to external influences such as adsorbates and strain, which can alter results. To address this problem, the Graphene Flagship project conducted an extensive benchmarking study of monolayer molybdenum disulfide grown through chemical vapor deposition by various groups. The study employed a variety of techniques to characterize the material, including optical and transmission electron microscopy, Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, and capacitance-voltage measurements. Herein, we present the results of this comprehensive study and the correlation between various methods

We present a benchmarking protocol that combines the characterization of boron nitride (BN) crystals and films with the evaluation of the electronic properties of graphene on these substrates. Our study includes hBN crystals grown under different conditions and scalable BN films deposited by either chemical or physical vapor deposition (CVD or PVD). We explore the complete process from boron nitride growth, over its optical characterization by time-resolved cathodoluminescence (TRCL), to the optical and electronic characterization of graphene by Raman spectroscopy after encapsulation and Hall bar processing. Within our benchmarking protocol we achieve a homogeneous electronic performance within each Hall bar device through a fast and reproducible processing routine. We find that a free exciton lifetime of 1 ns measured on as-grown hBN crystals by TRCL is sufficient to achieve high graphene room temperature charge carrier mobilities of 80,000 cm^2/(Vs) at a carrier density of |n| = 10^12 cm^-2, while respective exciton lifetimes around 100 ps yield mobilities up to 30,000 cm^2/(Vs). For scalable PVD-grown BN films, we measure carrier mobilities exceeding 10,000 cm^2/(Vs) which correlates with a graphene Raman 2D peak linewidth of 22 cm^-1. Our work highlights the importance of the Raman 2D linewidth of graphene as a critical metric that effectively assesses the interface quality (i.e. surface roughness) to the BN substrate, which directly affects the charge carrier mobility of graphene. Graphene 2D linewidth analysis is suitable for all BN substrates and is particularly advantageous when TRCL or BN Raman spectroscopy cannot be applied to specific BN materials such as amorphous or thin films. This underlines the superior role of spatially-resolved spectroscopy in the evaluation of BN crystals and films for the use of high-mobility graphene devices.

Two non-porous coordination compounds are presented as promising new materials for DMF sensing as they display a characteristic change of color and photoluminescence.

Strain engineering represents a pivotal approach to tailoring the optoelectronic properties of two-dimensional (2D) materials. However, typical bending experiments often encounter challenges, such as layer slippage and inefficient transfer of strain from the substrate to the 2D material, hindering the realization of their full potential. In our study, using molybdenum disulfide (MoS2) as a model 2D material, we have demonstrated that layers obtained through gold-assisted exfoliation on flexible polycarbonate substrates can achieve high-efficient strain transfer while also mitigating slippage effects, owing to the strong interfacial interaction established between MoS2 and gold. We employ differential reflectance and Raman spectroscopy for monitoring strain changes. We successfully applied uniaxial strains of up to 3% to trilayer MoS2, resulting in a notable energy shift of 168 meV. These values are comparable only to those obtained in encapsulated samples with organic polymers.

One of the main challenges to expand the use of titanium dioxide (titania) as a photocatalyst is related to its large band gap energy and the lack of an atomic scale description of the reduction mechanisms that may tailor the photocatalytic properties. We show that rutile TiO2 single crystals annealed in the presence of atomic hydrogen experience a strong reduction and structural rearrangement, yielding a material that exhibits enhanced light absorption, which extends from the ultraviolet to the near-infrared (NIR) spectral range, and improved photoelectrocatalytic performance. We demonstrate that both magnitudes behave oppositely: heavy/mild plasma reduction treatments lead to large/negligible spectral absorption changes and poor/enhanced (×10) photoelectrocatalytic performance, as judged from the higher photocurrent. To correlate the photoelectrochemical performance with the atomic and chemical structures of the hydrogen-reduced materials, we have modeled the process with in situ scanning tunneling microscopy measurements, which allow us to determine the initial stages of oxygen desorption and the desorption/diffusion of Ti atoms from the surface. This multiscale study opens a door toward improved materials for diverse applications such as more efficient rutile TiO2-based photoelectrocatalysts, green photothermal absorbers for solar energy applications, or NIR-sensing materials.

The wealth of complex polar topologies1-10 recently found in nanoscale ferroelectrics results from a delicate balance between the intrinsic tendency of the materials to develop a homogeneous polarization and the electric and mechanical boundary conditions imposed on them. Ferroelectric-dielectric interfaces are model systems in which polarization curling originates from open circuit-like electric boundary conditions, to avoid the build-up of polarization charges through the formation of flux-closure11-14 domains that evolve into vortex-like structures at the nanoscale15-17 level. Although ferroelectricity is known to couple strongly with strain (both homogeneous18 and inhomogeneous19,20), the effect of mechanical constraints21 on thin-film nanoscale ferroelectrics has been comparatively less explored because of the relative paucity of strain patterns that can be implemented experimentally. Here we show that the stacking of freestanding ferroelectric perovskite layers with controlled twist angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with the twisting. Furthermore, we find that a peculiar pattern of polarization vortices and antivortices emerges from the flexoelectric coupling of polarization to strain gradients. This finding provides opportunities to create two-dimensional high-density vortex crystals that would enable us to explore previously unknown physical effects and functionalities.

This work presents a straightforward, room-temperature synthesis of a robust {[Fe(atrz)(3)](OTs)(2)}(n) monolith. This approach offers a green alternative to traditional nanoparticle synthesis for manipulating spin crossover (SCO) behaviour. The monolith exhibits a more gradual SCO transition at lower temperatures compared to the bulk material, aligning with observations in smaller particle systems. Notably, the synthesis employs a solvent- and surfactant-free approach, simplifying the process and potentially reducing environmental impact, aligning with the principles of green chemistry.

We present the electrostatic control of photoluminescence of monolayer MoS$_2$ at room temperature via integration of free-standing BaTiO$_3$ (BTO), a ferroelectric perovskite oxide, layers. We show that the use of BTO leads to highly tunable exciton emission of MoS$_2$ in a minimal range of gate voltages, effectively controlling the neutral excitons to charged excitons (trions) conversion. Due to BTO's ferroelectric polarization-induced doping we observe large peak emission shifts as well as a large and tunable A trion binding energy in the range of 40-100 meV. To further investigate the efficacy of electrostatic control, we compared our measurements with those carried out when the BTO is replaced by a hexagonal boron nitride (hBN) dielectric layer of comparable thickness, confirming BTO's superior gating properties and thus lower power consumption. Additionally, we take advantage of the ferroelectric switching of BTO by fabricating devices where the BTO layer is decoupled from the gate electrode with a SiO$_2$ layer. Choosing to isolate the BTO allows us to induce large remanent behavior of MoS$_2$'s excitonic features, observing hysteretic behavior in the peak energy ratio between A exciton and its trion, as well as hysteretic behavior in the doping-related trion energy shift. This study illustrates the rich physics involved in combining free-standing complex oxide layers with two-dimensional materials.