arXiv subjects

Beatriz Martín-García

Publications and source records attributed to Beatriz Martín-García.

At least 19 recordsLinked to original sources

arXiv2026

A new helical InSeI polymorph: crystal structure and polarized Raman spectroscopy study

Tetragonal InSeI is an interesting low-dimensional metal chalcohalide due to its composition and anisotropic crystal structure composed of helical chains, which give rise to optoelectronic properties with potential application in photodetectors, optical thermometers, and spintronic devices. However, experimental works lack on the study of its anisotropic or chiral behavior. Here we present the crystal structure of an unreported InSeI polymorph and study its lattice dynamics in bulk crystals and exfoliated nanowires by polarized Raman spectroscopy for two non-equivalent crystallographic planes. We determine the orientation of the helical chains and distinguish between crystallographic planes by linearly polarized measurements, evaluating the angle-dependent intensity of the modes, which allows assigning each mode to its representation. Circularly polarized Raman measurements do not reveal chiral phonons, despite the helical chains and anisotropic crystal structure. These results offer insight into the crystal structure of InSeI, which is fundamental for the fabrication of orientation-dependent optoelectronic and spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Engineering magnetism in hybrid organic-inorganic metal halide perovskites

The chemical and structural flexibility of hybrid organic-inorganic metal halide perovskites (HOIPs) provides an ideal platform for engineering not only their well-studied optical properties, but also their magnetic ones. In this review we present HOIPs from a new perspective, turning the attention to their magnetic properties and their potential as new class of on-demand low-dimensional magnetic materials. Focusing on HOIPs containing transition metals, we comprehensively present the progress that has been made in preparing, understanding and exploring magnetic HOIPs. First, we briefly introduce HOIPs in terms of composition and crystal structure and examine the synthesis protocols commonly used to prepare those showing magnetic properties. Then, we present their rich magnetic behavior and phenomenology; discuss their origin and guidelines for tuning them by changing the perovskite phase, chemical composition and dimensionality; and showcase their potential application in magneto-optoelectronics and spintronics. Finally, we describe the current challenges in the field, such as their integration into devices, as well as the emerging possibilities of moving from magnetic doping to pure transition metal-based HOIPs, which will motivate further studies in the future.

cond-mat.mtrl-sci↗

arXiv2026

Galvanic intercalation of molecular cations into van der Waals materials

The intercalation of molecular species between the layers of van der Waals (vdW) crystals is a powerful approach to combine the remarkable physical properties of vdW materials with the chemical versatility of organic molecules. However, the full transformative potential of molecular intercalation remains underexplored, largely due to the lack of simple, broadly applicable methods that preserve high crystalline quality down to the few-layer limit. Here, we introduce a simple galvanic approach to intercalate different molecules into various vdW materials under ambient conditions, leveraging the low reduction potential of selected metals. We employ our method, which is particularly well-suited for the in-situ intercalation of few-layer-thick crystals, to intercalate nine vdW materials, including magnets and superconductors, with molecules ranging from conventional alkylammonium ions to metallorganic and bio-inspired chiral cations. Notably, intercalation leads to an unprecedented transition from antiferromagnetic to ferrimagnetic ordering in α-RuCl3 and to a molecule-dependent enhancement of the superconducting transition in 2H-TaS2. These results establish our approach as a versatile technique for engineering atomically thin quantum materials and heterostructures, unlocking the transformative effects of molecular intercalation.

cond-mat.mtrl-sci↗

arXiv2026

Ferromagnetism above 200 K in organic-ion intercalated CrSBr

CrSBr is a van der Waals magnetic semiconductor exhibiting antiferromagnetic order below 140 K. It has emerged as a promising platform for engineering 2D magnetism because its intertwined electronic, optical, and magnetic properties can be profoundly modified via external stimuli such as electrical gating or magnetic fields. However, other strategies for tuning magnetism in layered materials, such as molecular intercalation, remain largely unexplored for CrSBr. Here, we demonstrate that the intercalation of tetramethylammonium (TMA) and tetrapropylammonium (TPA) ions into CrSBr induces a transition from antiferromagnetic to ferromagnetic order, while significantly enhancing the magnetic transition temperature to 190 K (TMA) and 230 K (TPA). The resulting intercalates are air-stable and exhibit large, hysteretic magnetoresistance exceeding 60% at 50 K in the TPA case. Besides, intercalation introduces symmetry-breaking structural changes in each CrSBr plane, revealed by Raman microscopy and corroborated by density functional theory (DFT) calculations. These findings highlight molecular intercalation as a powerful and versatile route to tailor the magnetic properties of CrSBr and unlock its potential to fabricate robust, high-temperature 2D magnetic devices.

cond-mat.mtrl-sci↗

arXiv2026

Unveiling Photoluminescence Signatures of Magneto-Optical Coupling in Layered Hybrid Manganese Chloride Perovskites

Understanding the interplay between magnetic ordering and light emission is crucial for developing magneto-optical technologies. However, this phenomenon is poorly understood since observations of this coupling vary significantly across materials. In this context, hybrid organic-inorganic metal halide perovskites (HOIPs) that incorporate Mn2+ ions are a chemically and structurally tunable platform for exploring this phenomenon, since they exhibit magnetic ordering and photoluminescence (PL) emission. Here, we study two antiferromagnetic Mn-based HOIPs with different organic cations that result in distinct lattice stiffness, Mn2+-Mn2+ distance and octahedral distortion. Temperature-dependent PL excitation spectroscopy reveals changes in crystal field splitting energy and Racah parameters well above the Néel temperature (TN), indicating the emergence of Mn2+-Mn2+ magnetic interactions prior to reach long-range magnetic ordering. These variations align with the observed changes in temperature-PL evolution. The compound with a more rigid lattice shows stronger changes closer to TN, suggesting combined effects of magnetic polarons and spin-canting. In contrast, magnetic polaron-induced magnetic modifications prevail in the HOIP with a softer lattice. These results reveal the complexity of the magneto-optical coupling in Mn-based HOIPs and provide new insights into this field extensible to other 2D materials that exhibit this phenomenon with potential for advanced magneto-optical applications.

cond-mat.mtrl-sci↗

arXiv2026

Permanent Lattice Compression of Lead-Halide Perovskite for Persistently Enhanced Optoelectronic Properties

Under mild mechanical pressure, halide perovskites show enhanced optoelectronic properties. However, these improvements are reversible upon decompression, and permanent enhancements have yet to be realized. Here, we report antisolvent-assisted solvent acidolysis crystallization that enables us to prepare methylammonium lead bromide single crystals showing intense emission at all four edges under ultraviolet light excitation. We study structural variations, edge-vs-center, in these crystals using micro-X-ray diffraction and find that the enhanced emission at the edges correlates with lattice compression compared to in the central areas. Time-resolved photoluminescence measurements show much longer-lived photogenerated carriers at the compressed edges, with radiative component lifetimes of ca. 1.4 us, 10 times longer than at the central regions. The properties of the edges are exploited to fabricate planar photodetectors exhibiting detectivities of 3x10^13 Jones, compared to 5x10^12 Jones at the central regions. The enhanced lifetimes and detectivities correlate to the reduced trap state densities and the formation of shallower traps at the edges due to lattice compression.

cond-mat.mtrl-sci↗

arXiv2026

Graphene-based technologies for energy applications, challenges and perspectives

Here we report on technology developments implemented into the Graphene Flagship European project for the integration of graphene and graphene-related materials (GRMs) into energy application devices. Many of the technologies investigated so far aim at producing composite materials associating graphene or GRMs with either metal or semiconducting nanocrystals or other carbon nanostructures (e.g., CNT, graphite). These composites can be used favourably as hydrogen storage materials or solar cell absorbers. They can also provide better performing electrodes for fuel cells, batteries, or supercapacitors. For photovoltaic (PV) electrodes, where thin layers and interface engineering are required, surface technologies are preferred. We are using conventional vacuum processes to integrate graphene as well as radically new approaches based on laser irradiation strategies. For each application, the potential of implemented technologies is then presented on the basis of selected experimental and modelling results. It is shown in particular how some of these technologies can maximize the benefit taken from GRM integration. The technical challenges still to be addressed are highlighted and perspectives derived from the running works emphasized.

cond-mat.mtrl-sci↗

arXiv2026

Functionalization of reduced graphite oxide sheets with a zwitterionic surfactant

Films of a few layers in thickness of reduced graphite oxide, RGO, sheets functionalized by the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, DDPS, are obtained by using the Langmuir-Blodgett method. The quality of the RGO sheets is checked by analyzing the degrees of reduction and defect repair by means of X-ray photoelectron spectroscopy, atomic force microscopy -AFM, field-emission scanning electron microscopy -SEM, micro-Raman spectroscopy, and electrical conductivity measurements. A modified Hummers method is used to obtain highly oxidized graphite oxide, GO, together with a centrifugation-based method to improve the quality of GO. The GO samples are reduced by hydrazine or vitamin C. Functionalization of RGO with the zwitterionic surfactant improves the degrees of reduction and defect repair of the two reducing agents and significantly increases the electrical conductivity of paperlike films compared with those prepared from unfunctionalized RGO.

cond-mat.mtrl-sci↗

arXiv2026

Langmuir and Langmuir-Blodgett films of a maleic anhydride derivative: effect of subphase divalent cations

We report the study of the equilibrium and dynamic properties of Langmuir monolayers of poly (styrene-co-maleic anhydride) partial 2-buthoxy ethyl ester cumene terminated polymer and the effect of the Mg(NO3)2 addition in the water subphase on the film properties. Results show that the polymer monolayer becomes more expanded when the electrolyte concentration in the subphase increases. Dense polymer films aggregate at the interface. The aggregates are transferred onto Silicon wafers using the Langmuir-Blodgett methodology and the morphology is observed by AFM. The structure of aggregates depends on the subphase composition of the Langmuir film transferred onto the silicon wafer.

cond-mat.mtrl-sci↗

arXiv2026

Photoluminescence Dynamics of CdSe QD/polymer Langmuir-Blodgett Thin Films: Morphology Effects

Thin films of colloidal semiconductor CdSe quantum-dots (QDs) and a styrene/maleic anhydride copolymer were prepared by the Langmuir-Blodgett technique and their photoluminescence was characterized by confocal fluorescence lifetime microscopy. In the films, the photoluminescence dynamics are strongly affected by excitation energy migration between close-packed quantum-dots and energy trapping by surface-defective QDs or small clusters of aggregated QDs. Polymer/QD films with more aggregated QD regions exhibit lower PL intensities and faster decays, which we attribute primarily to the increased ability of excitations to find trap sites among more close-packed QD regions. This was confirmed by comparing films from bilayer or co-spreading deposition, and varying the QD-to-polymer composition or the surface pressure at deposition. The more regular films, such as those obtained by bilayer deposition at high-pressure, display more surface emission intensity and decays with less accentuated curvature. Decay analysis was performed with a model that accounts for excitation energy migration and trapping in the films. In the framework of the model, the photoluminescence dynamics are related to film morphology through the density of energy traps. A lower amount of QD clustering in the films reflects on a lower density of energy traps and, thus, on more emissive QD films, as inferred here for bilayer films relatively to co-spreading films.

cond-mat.mtrl-sci↗

arXiv2026

Nanoparticle Self-assembly Assisted by Polymers: The Role of Shear Stress in the Nanoparticle Arrangement of Langmuir and Langmuir-Blodgett Films

We propose to use the self-assembly ability of a block copolymer combined with compression-expansion cycles to obtain CdSe quantum dots (QDs) structures of different morphology. The methodology proposed consists in transferring onto mica mixed Langmuir monolayers of QDs and the polymer poly (styrene-co-maleic anhydride) partial 2 buthoxy ethyl ester cumene terminated, PS-MA-BEE, previously sheared by 50 compression-expansion cycles. Results indicate that the shear stress takes out nanoparticles at the air-water interface from metastable states and promoted a new equilibrium state of the Langmuir monolayer, then it was transferred onto mica by the Langmuir-Blodgett (LB) methodology and the morphology of the LB films was analyzed by Atomic Force Microscopy and Transmission Electron Microscopy measurements. Our results show that when the amplitude strain increases the QDs domain size decreases and the LB film becomes more ordered. The dynamic of the monolayer relaxation after cycling involves at least three timescales which are related to the damping of surface fluctuation, raft rearrangement and component movements inside each raft. Brewster Angle Microscopy allowed visualizing in situ the raft rearrangement at the air-water interface.

cond-mat.mtrl-sci↗

arXiv2026

Efficient charge transfer in solution-processed PbS Quantum Dot-reduced graphene oxide hybrid materials

Quantum dot - graphene hybrid materials have raised significant interest due to the unique synergy of the optical properties of colloidal quantum dots (QDs) and the transport properties of graphene. This stimulated the development of low-cost and up-scalable solution-processed strategies for hybrid materials with potential application in light harvesting and opto-electronic devices. Here we report a versatile covalent-linking based approach for the functionalization of reduced graphene oxide (rGO), to prepare a variety of QD-rGO hybrid dispersions with QDs of different size and composition (PbS, PbS/CdS and CdSe QDs), and shape (CdSe/CdS dot-in-rods). We achieved a well-controlled QD coverage of the rGO sheets by functionalizing the rGO surface with mercapto-silane linkers. A further spectroscopic investigation of near-infrared PbS QD-rGO materials demonstrates efficient electronic coupling between both materials. The QD photoluminescence emission quenching and exciton lifetime shortening up to 95%, together with subtle graphene Raman G-band shifts upon QD linking, supports electron transfer as the dominant relaxation pathway from the QD to the rGO. The use of core/shell PbS/CdS QDs allows tuning of the transfer efficiency from 94% for a 0.2 nm thin CdS shell, down to 30% for a 1.1 nm thick shell.

cond-mat.mes-hall↗

arXiv2026

Phase Transitions in Low-Dimensional Layered Double Perovskites: The Role of the Organic Moieties

Halide double perovskites are an interesting alternative to Pb-containing counterparts as active materials in optoelectronic devices. Low-dimensional double perovskites are fabricated by introducing large organic cations, resulting in organic/inorganic architectures with one or more inorganic octahedral layers separated by organic cations. Here, we synthesize layered double perovskites based on 3D Cs2AgBiBr6 that consist of double (2L) or single (1L) inorganic octahedral layers, using ammonium cations of different size and chemical structure. Temperature-dependent Raman spectroscopy reveals phase transition signatures in both inorganic lattice and organic moieties by detecting variations in their vibrational modes. Changes in the conformational arrangement of the organic cations to an ordered state coincide with a phase transition in the 1L systems with the shortest ammonium moieties. Significant changes of photoluminescence intensity observed around the transition temperature suggest that optical properties may be deeply affected by the octahedral tilts emerging at the phase transition.

cond-mat.mtrl-sci↗

arXiv2026

Gate-tunable charge-spin interconversion in graphene/heavy-metal heterostructures

Spintronics has emerged as a promising field for next-generation devices, offering functionalities beyond complementary metal-oxide-semiconductor (CMOS). A critical challenge in spintronics is to develop systems that can efficiently generate spin currents and enable their long-distance transport. Here, we demonstrate a graphene (Gr)/heavy metal (HM) heterostructure system that combines strong charge-spin interconversion efficiency, induced by the spin Hall effect, with a long spin diffusion length. By employing an industry-friendly magnetron sputtering technique, we deposit HM layers onto few-layer Gr while minimizing structural damage. The proximity effect from the HM enhances the spin Hall angle of Gr while limiting the reduction in its spin diffusion length. Additionally, the spin Hall angle can be tuned via an applied gate voltage, offering high controllability of the system. Importantly, these properties are observed across heterostructures composed of different HMs, indicating the generality of this approach. Our findings establish Gr/HM heterostructures as a scalable and versatile platform for spin current generation, paving the way for advanced spintronic devices with high efficiency, long spin propagation, and straightforward fabrication processes.

cond-mat.mes-hall↗

arXiv2025

Lattice dynamics in chiral tellurium by linear and circularly polarized Raman spectroscopy: crystal orientation and handedness

Trigonal tellurium (Te) has attracted researchers' attention due to its transport and optical properties, which include electrical magneto-chiral anisotropy, spin polarization and bulk photovoltaic effect. It is the anisotropic and chiral crystal structure of Te that drive these properties, so the determination of its crystallographic orientation and handedness is key to their study. Here we explore the structural dynamics of Te bulk crystals by angle-dependent linearly polarized Raman spectroscopy and symmetry rules in three different crystallographic orientations. The angle-dependent intensity of the modes allows us to determine the arrangement of the helical chains and distinguish between crystallographic planes parallel and perpendicular to the chain axis. Furthermore, under different configurations of circularly polarized Raman measurements and crystal orientations, we observe the shift of two phonon modes only in the (0 0 1) plane. The shift is positive or negative depending on the handedness of the crystals, which we determine univocally by chemical etching. Our analysis of three different crystal faces of Te highlights the importance of selecting the proper orientation and crystallographic plane when investigating the transport and optical properties of this material. These results offer insight into the crystal structure and symmetry in other anisotropic and chiral materials, and open new paths to select a suitable crystal orientation when fabricating devices.

cond-mat.mtrl-sci↗

arXiv2025

Enhanced Superconductivity in 2H-TaS2 Devices Through in-situ Molecular Intercalation

The intercalation of guest species into the gap of van der Waals materials often leads to the emergence of intriguing phenomena, such as superconductivity. While intercalation-induced superconductivity has been reported in several bulk crystals, reaching a zero-resistance state in flakes remains challenging. Here, we show a simple method for enhancing the superconducting transition in tens-of-nm thick 2H-TaS2 crystals contacted by gold electrodes through in-situ intercalation. Our approach enables measuring the electrical characteristics of the same flake before and after intercalation, permitting us to precisely identify the effect of the guest species on the TaS2 transport properties. We find that the intercalation of amylamine molecules into TaS2 flakes causes a suppression of the charge density wave and an increase in the superconducting transition, with an onset temperature above 3 K. Additionally, we show that a fully developed zero-resistance state can be achieved in flakes by engineering the conditions of the chemical intercalation. Our findings pave the way for the integration of chemically tailored intercalation compounds in scalable quantum technologies.

cond-mat.supr-con↗

arXiv2025

Unconventional magnon transport in antiferromagnet NiPS$_3$ induced by an anisotropic spin-flop transition

Nonlocal magnon transport can provide valuable insight into the magnetic properties of magnetic insulators (MIs). A spin-flop transition, a typical magnetic reorientation in antiferromagnets, is expected to affect mag non transport, but studies on this topic are still rare and remain challenging, especially for van der Waals materials. Here we demonstrate the unconventional magnon transport driven by an anisotropic spin-flop transition in the van der Waals antiferromagnet NiPS$_3$. Examining the nonlocal voltage from thermally driven magnons reveals sharp jumps at certain directions when an inplane magnetic field aligns with the b-axis of NiPS$_3$, attributed to an in-plane anisotropic spin-flop transition. Furthermore, thermally driven magnon signal exhibits a 1/d$^2$ decay in thin NiPS$_3$, evidencing that it is dominated by the intrinsic spin Seebeck effect. Our findings highlight that the electrical detection of magnon currents in a nonlocal device geometry serves as a powerful approach for studying magnetic phase transitions in MIs.

cond-mat.mes-hall↗

arXiv2025

Symmetry Origin and Microscopic Mechanism of Electrical Magnetochiral Anisotropy in Tellurium

Non-linear transport effects in response to external magnetic fields, i.e. electrical magnetochiral anisotropy (eMChA), have attracted much attention for their importance to study quantum and spin-related phenomena. Indeed, they have permitted the exploration of topological surface states and charge-to-spin conversion processes in low-symmetry systems. Nevertheless, despite the inherent correlation between the symmetry of the material under examination and its non-linear transport characteristics, there is a lack of experimental demonstration to delve into this relationship and to unveil their microscopic mechanisms. Here, we study eMChA in chiral elemental Tellurium (Te) along different crystallographic directions, establishing the connection between the different eMChA components and the crystal symmetry of Te. We observed different longitudinal eMChA components with collinear current and magnetic field, demonstrating experimentally the radial angular momentum texture of Te. We also measured a transverse non-linear resistance which, as the longitudinal counterpart, scales bilinearly with current and magnetic fields, illustrating that they are different manifestations of the same effect. Finally, we study the scaling law of the eMChA, evidencing that extrinsic scattering from dynamic sources is the dominant microscopic mechanism. These findings underscore the efficacy of symmetry-based investigations in understanding and predicting non-linear transport phenomena, with potential applications in spintronics and energy harvesting.

cond-mat.mes-hall↗