arXiv subjects

José J. Baldoví

Publications and source records attributed to José J. Baldoví.

At least 19 recordsLinked to original sources

arXiv2026

WannierSTM: Efficient superconducting scanning-probe spectroscopy from maximally localized Wannier functions

We present a Python-based program that combines maximally localized Wannier functions-based first-principles electronic structure with the nonequilibrium Green's function formalism to enable efficient simulations of scanning tunneling microscopy (STM). The workflow builds upon standard density functional theory packages to construct compact transport Hamiltonians that preserve the properties of realistic materials. Superconductivity is incorporated via an effective pairing potential within the Nambu-spinor formalism, while coupling to the STM tip and substrate electrodes is treated using the wide-band limit approximation. Within this formulation, transport quantities such as current-voltage characteristics and differential conductance are evaluated in a closed analytical form. This avoids explicit numerical energy integrations and enables rapid spectroscopic calculations over broad parameter spaces. The framework provides a unified and computationally efficient approach for modeling superconducting hybrid nanostructures with spin-orbit coupling, magnetic textures, and spin polarization. Representative applications in spin chains, two-dimensional and molecular magnets on a superconductor demonstrate its robust capabilities for both simple model systems and realistic ab initio molecular structures relevant to modern STM experiments.

cond-mat.mes-hall↗

arXiv2026

Intrinsic (non)-Gilbert damping in magnetic insulators calculated from a minimal model and ab initio spin Hamiltonians

We present an analytically solvable minimal model for the relaxation of low-frequency magnons in magnetic insulators arising from magnon-phonon and magnon-magnon interactions. The model establishes a direct connection between microscopic relaxation processes and Gilbert damping, and reveals how magnon decay evolves from bulk systems to the monolayer limit. We find that magnon-phonon coupling produces Gilbert damping of comparable magnitude in three- and two-dimensional magnets, with qualitative differences between flexural phonons in free-standing monolayers and three-dimensional phonons in substrate-supported layers. By contrast, non-Gilbert damping due to four-magnon scattering is strongly enhanced in two dimensions, where it becomes independent of spin-orbit coupling. To benchmark the model against real materials, we introduce a numerical approach for computing magnon damping from ab initio-derived spin Hamiltonians. We demonstrate that the central conclusions of the model remain valid for magnons in bulk YIG and several van der Waals magnetic insulators: CrSBr, CrI3 and CrPS4.

cond-mat.mtrl-sci↗

arXiv2026

Switchable Altermagnetism in a Layered van der Waals Metal-Organic Framework Driven by Spin-Crossover

Dynamical control of altermagnetism is a key requirement for translating its unique spin-dependent functionalities into practical spintronic devices, yet effective switching mechanisms remain largely unexplored. Here, we open an unprecedented, versatile and programmable route based on spin-crossover to switch altermagnetism on demand in molecular materials. Using density functional calculations, we demonstrate an altermagnetic ground state in the layered van der Waals MOFs MnX$_2$(tdz)$_2$ (X = Cl, Br; tdz = thiadiazole), stabilized by anisotropic interlayer exchange interactions, which gives rise to a characteristic d-wave momentum-space spin splitting and an associated spin-splitter transport response. Our findings reveal that under hydrostatic pressure, a high-spin to low-spin transition reconfigures the Mn d-orbital occupation, thus modifying the magnetic exchange network, and stabilizing a different antiferromagnetic ground state whose symmetry suppresses the nonrelativistic spin splitting. Crucially, spin-crossover switches altermagnetism not by directly altering the electronic structure, but by changing the symmetry of the magnetic ground state. These results establish molecular spin-crossover altermagnets as a platform for externally reconfigurable spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Electrical Control of Altermagnetism in a Quasi-1D Magnet

Altermagnetism is a collinear magnetic state characterized by momentum-dependent spin splitting in fully compensated materials. While widely investigated in systems governed by three- or two-dimensional exchange interactions, its extension to quasi-one-dimensional magnets remains almost unexplored. Focusing on the experimentally established AgCrP$_2$S$_6$ van der Waals magnet, we demonstrate that antiferromagnetic chains embedded in a two-dimensional lattice provide a general route to altermagnetism. Combining first-principles calculations and spin-space-group analysis, we show that out-of-plane symmetry breaking can generate a nonrelativistic d-wave spin splitting. An external out-of-plane electric field validates this mechanism, where the induced splitting increases linearly with field strength and reverses sign with field direction. We rationalize such behaviour by constructing an effective tight-binding model, which links the altermagnetic response to anisotropic third-neighbor interchain hoppings. Additionally, we show that Janus substitution also induces a d-wave spin texture, while ferroelectric interfacing with CuInP$_2$S$_6$ enables polarization-controlled spin-split bands in a fully compensated ferrimagnetic state. Our results establish quasi-one-dimensional antiferromagnets as building blocks for altermagnetism.

cond-mat.mtrl-sci↗

arXiv2026

Twist-engineering of a robust Quantum Spin Hall phase in $β$-/flat bismuthene bilayer from first principles

Twist-engineering of topological phases in two-dimensional materials offers a powerful route to modulate electronic structure beyond conventional strain or chemical control. In particular, group 15 (pnictogens) monolayers such as bismuthene provide an ideal platform due to their strong intrinsic spin-orbit coupling (SOC) and robust topological character. Here, we investigate a previously unexplored heterostructure consisting of a $β$-bismuthene monolayer rotated by 30$^\circ$ on a planar bismuthene layer stabilized on a SiC(0001) substrate. Using first-principles calculations, we demonstrate that this specific rotational alignment induces a unique interlayer orbital hybridization which, combined with the strong SOC and the naturally broken inversion symmetry, gives rise to a pronounced Rashba spin-splitting, absent in the isolated monolayers. The topological nature of the system is confirmed through the calculation of the Z2 topological invariant and Spin Hall Conductivity (SHC), revealing a robust Quantum Spin Hall (QSH) phase with an enhanced topological response compared to the individual layers. Furthermore, we explore the chemical tunability of this system via Sb substitution, showing that the gradual reduction of SOC systematically narrows the band gap while preserving the non-trivial topology. Our results establish large-angle twisted group 15 heterostructures as a versatile platform for engineering spin-orbit-driven phenomena and advancing topological spintronics.

cond-mat.mtrl-sci↗

arXiv2026

Emergent $d$-wave altermagnetism in orthogonally twisted bilayer CrPS$_4$

Twistronics is a powerful strategy to engineer novel quantum states by controlling the relative orientation between layered materials. Here, we demonstrate that an orthogonally twisted bilayer CrPS$_4$ shows $d$-wave altermagnetism driven purely by structural rotation. Symmetry analysis reveals that the twisted stacking breaks partial translational combined with time-reversal symmetry, leading to a fourfold rotation relation between opposite spin sublattices, enabling altermagnetism. First-principles calculations demonstrate a sizable non-relativistic spin splitting of up to 68 meV around the Fermi level. We further show that the altermagnetic state can be further stabilized through interlayer compression and modulation of the on-site Coulomb interaction. The resulting band structure exhibits pronounced spin-dependent anisotropy, enabling efficient spin to charge conversion reaching $\sim$50% near the Fermi level and sizable giant magnetoresistance. These results establish twisted CrPS$_4$ as a realistic platform for altermagnetism and highlights twistronics as a versatile route for advanced spintronics applications.

cond-mat.mtrl-sci↗

arXiv2026

One-Dimensional Materials Supported in Two-Dimensional van der Waals Metal-Organic Frameworks with Optical Anisotropy Switching via Twist-Engineering

Van der Waals (vdW) materials provide a platform to study and control the physical properties of low-dimensional materials. While strategies developed for two-dimensional (2D) crystals are not directly transferable to one-dimensional (1D) systems, we can benefit from them by creating layers formed by interconnected chains. Here, we develop a molecular strategy to illustrate this concept consisting of assembling 1D materials in 2D metal-organic frameworks (MOFs). Crystals of [FeX(pzX)(bpy)] (X = Cl, F; pz = pyrazole; bpy = bipyridine) consist of iron chains along the b-axis, crosslinked via bpy ligands along the a-axis to form 2D layers, stacked along the c-axis via vdW forces. This structural anisotropy manifests itself in highly-anisotropic optical properties, as demonstrated by optical measurements in the visible and terahertz ranges, results which are supported by DFT calculations. Chemical substitution enables the tuning of the optical properties, as exemplified by the photoluminescence of the Cl-derivative, which is quenched for the F-derivative. Thin-layers are obtained by mechanical exfoliation, and their optical properties are further tuned through the fabrication of orthogonally-twisted vdW heterostructures, enabling to effectively switch-off the optical anisotropy. Our work highlights the chemical flexibility of vdW layered MOFs as a platform for designing and manipulating 1D architectures.

cond-mat.mtrl-sci↗

arXiv2026

Altermagnetic Metal-Organic Frameworks

Altermagnetism has recently emerged as a new class of spin compensated magnetic materials that exhibit momentum dependent spin splitting despite having zero net magnetization. The origin of these electronic signatures lies in symmetry operations that connect opposite spin sublattices while allowing spin splitting in momentum space. While most candidate materials identified so far belong to inorganic crystals with fixed lattice symmetries, the realization of altermagnetism ultimately requires platforms in which magnetic symmetry can be deliberately engineered. In this Perspective, we discuss how metal-organic frameworks (MOFs) provide a unique chemical platform to address this challenge. We first place altermagnetism in the broader context of magnetic and electronically active metal-organic networks, highlighting how reticular chemistry enables precise control over lattice geometry, dimensionality and electronic structure. We then discuss how these features position framework materials as promising candidates for realizing altermagnetism and highlight the key challenges that must be addressed to translate theoretical proposals into experimentally accessible systems. Finally, we critically assess current experimental challenges and outline emerging directions for realizing and controlling altermagnetism in coordination framework materials, which emerge as a versatile and powerful platform for exploring new paradigms in spintronics.

cond-mat.mtrl-sci↗

arXiv2026

Twist-induced altermagnetism in a metallic van der Waals antiferromagnet

Altermagnetism -a magnetic state characterized by spin-polarized electronic bands at zero net magnetization- offers a promising route for next-generation spintronic devices. In two-dimensional (2D) magnets, twist engineering enables its realization by breaking the combined inversion and time-reversal symmetry (PT) while preserving crystal symmetries that ensure the altermagnetic order. Here, by means of first-principles calculations and symmetry analysis, we demonstrate that twist engineering applied to the recently synthesized metallic van der Waals antiferromagnet Co-doped bilayer Fe$_3$GaTe$_2$ (Fe$_2$CoGaTe$_2$) provides a robust platform for altermagnetism. By twisting two layers of Fe$_2$CoGaTe$_2$, the PT symmetry between opposite spin sublattices is broken, resulting in a non-relativistic $i$-wave altermagnetic state with spin splitting up to 138 meV. In the absence of spin-orbit coupling (SOC), the electronic states are spin-degenerate along six high-symmetry directions, while the inclusion of SOC preserves this degeneracy along the three directions protected by twofold rotation axes. Furthermore, we unveil the microscopic mechanisms governing the magnetic behavior in twisted Fe$_2$CoGaTe$_2$. Our results establish twist engineering and metallic Fe-based van der Waals antiferromagnets as versatile platforms to realize 2D van der Waals altermagnetism, with potential for designing high-efficiency ultrathin nanodevices.

cond-mat.mtrl-sci↗

arXiv2025

Switchable Magnonic Crystals Based on Spin Crossover/CrSBr Heterostructures

The progress of magnonics ultimately depends on material platforms that offer precise control of spin waves propagation. Here, we put forward a chemical strategy to create locally tunable magnonic crystals by integrating switchable spin-crossover (SCO) molecules with 2D van der Waals magnets. Specifically, we investigate from first principles a hybrid molecular/2D heterostructure formed by [Fe((3,5-(CH3)2Pz)3BH)2] molecules (Fe-pz) deposited on a single-layer of semiconducting CrSBr. We show that Fe-pz molecules are stable on CrSBr while preserving its SCO bistability, particularly in densely packed molecular arrays. By patterning Fe-pz into periodic stripes separated by pristine CrSBr regions, the interface becomes a magnonic crystal that filters spin waves at selected frequencies. Crucially, light-driven excited spin-state trapping (LIESST) enables LS-HS switching and induces up to ~1.3% local strain in CrSBr, which in turn reshapes the magnonic band structure in a dynamic and reversible manner. These results establish Fe-pz@CrSBr as a switchable platform for on-chip, programmable magnonic devices.

cond-mat.mtrl-sci↗

arXiv2025

Chemical Engineering of Altermagnetism in Two-Dimensional Metal-Organic Frameworks

Altermagnetism represents a novel class of collinear antiferromagnetism exhibiting non-relativistic spin splitting without net magnetization, driven by lattice symmetry rather than spin-orbit coupling (SOC). Here, we introduce a coordination-driven chemical strategy to realize altermagnetic (AM) spin splitting in two-dimensional (2D) planar tetracoordinated Cr-based metal-organic frameworks (MOFs). Using density functional theory (DFT) calculations, we demonstrate that replacing centrosymmetric pyrazine (pyz) ligands with non-centrosymmetric imidazole (imz) linkers in Cr-based MOFs reduces lattice symmetry, enabling g-wave AM spin splitting up to 65 meV. Furthermore, frontier molecular orbital engineering (FMOE) allows selective ligand spin polarization, inducing a shift to d-wave AM anisotropy in polycyclic ligand-based 2D MOFs with spin splitting up to 83.9 meV. Microscopic magnetic exchange interactions (J) analysis reveals that ligand-mediated interactions dominate over metal-metal coupling, stabilizing AM order in systems with radical ligands. Interestingly, we further confirm AM spin splitting in spin wave spectrum, where chiral magnon splitting is observed. Finally, we show that AM spin splitting gives rise to experimentally accessible charge to spin conversion, emerging as a linear response in d-wave and as a symmetry-allowed nonlinear effect in g-wave 2D AM MOFs. This work establishes coordination chemistry as a powerful and versatile route to symmetry control in 2D MOFs, enabling rational design of 2D molecular materials with tunable electronic and AM properties for next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Anisotropic Phonon Dynamics and Directional Transport in Actinide van der Waals Semiconductor USe$_3$

Direction-dependent charge transport and optical responses are characteristic of van der Waals (vdW) materials with strong in-plane anisotropy. While transition-metal trichalcogenides (TMTCs) exemplify this behavior, heavier analogs remain largely unexplored. In this study we examine USe$_3$ as an anisotropic vdW material and a heavier analog of the well-studied TMTCs. We reveal strong in-plane anisotropy using polarization-resolved Raman spectroscopy, investigate strain-induced shifts of phonon modes, and quantify direction-dependent charge-carrier mobility through transport measurements on field-effect devices. First-principles calculations based on density-functional theory corroborate our findings, providing a theoretical basis for our experimental observations. Casting USe$_3$ as an actinide analog of a TMTC establishes a platform for exploring low-dimensional semiconductors that combine strong in-plane anisotropy with f-electron physics.

cond-mat.mtrl-sci↗

arXiv2025

Confinement-Induced One-Dimensional Magnetism in CrSBr Chains via Carbon Nanotube Encapsulation

Encapsulating low-dimensional magnetic materials within carbon nanotubes (CNTs) offers a compelling route to stabilize unconventional magnetic states and engineer quantum functionalities at the limit of miniaturization. In this work, we systematically investigate the structural, electronic, and magnetic properties of one-dimensional (1D) CrSBr chains encapsulated within CNTs using density functional theory (DFT) and spin dynamics simulations. We demonstrate the structural stability of CrSBr@CNT, where confinement and charge transfer cooperate to stabilize ferromagnetism in the 1D limit, which persists up to 50 K. These findings position CrSBr@CNT as a model platform for realizing 1D magnetism and establish CNT encapsulation as a powerful strategy for exploring emergent quantum spin phenomena and engineering nanoscale spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Excitonic optical absorption in strained monolayer CrSBr

Recently, the isolation of 2D magnetic materials has opened several avenues for possible new ap- plications in spintronics. Among these materials, CrSBr has sparked interest due to its relatively high Curie temperature, highly anisotropic lattice structure, and high structural stability. These properties ran along others shared by any atomically thin material such as its outstanding defor- mation capacity and a strong optical response dominated by excitonic effects. The combination of these properties provides a fairly uncharted playground where to explore the interplay between magnetism and optical excitations. Here, we focus our attention on the theoretical optical response of CrSBr under several distinct strain configurations, analyzing the resulting changes to both the excitonic peaks and overall shape of the diagonal components of the linear conductivity tensor.

cond-mat.mes-hall↗

arXiv2025

Controlling Magnetism in the 2D van der Waals Antiferromagnet CrPS$_4$ via Ion Intercalation

Two-dimensional van der Waals (vdW) magnetic materials are versatile platforms for tailoring electronic and magnetic properties, in which the insertion of chemical species into their interlayer gaps offers a powerful route to engineer magnetism. Here, we focus on the A-type antiferromagnetic semiconductor CrPS$_4$ (T$_N$ = 38 K) and investigate its electronic and magnetic properties upon intercalation of lithium (Li$^+$) and organic tetrabutylammonium (TBA$^+$) ions using first-principles calculations. Our results show that Li$^+$ incorporation induces a semiconductor-to-metal transition in CrPS$_4$ and selectively modifies its magnetic behaviour: switching from out-of-plane to in-plane antiferromagnetism, followed by an in-plane ferromagnetic ground state at higher intercalation levels. This is accompanied by a continuous increase of the ordering temperature, reaching a fivefold enhancement for Li$_{0.5}$CrPS$_4$. Similarly, TBA$^+$ intercalation expands the vdW gap, decoupling CrPS$_4$ layers and stabilising in-plane ferromagnetism with a T$_C$ above 100 K. Furthermore, it also modifies magnon propagation, leading to enhanced group velocities and a more isotropic magnon transport. This work highlights intercalation as a powerful and versatile approach for controlling magnetic behaviour and spin dynamics, paving the way for the design of tunable 2D layered magnetic materials for spintronic and magnonic applications.

cond-mat.mtrl-sci↗

arXiv2025

Electronic band structure from quasiparticle interference and Landau quantization in WTe$_2$

WTe$_2$ stands out as a semimetal presenting Fermi level quantum oscillations in most measured quantities under magnetic fields. However, the electronic band structure above and below the Fermi level has not been explored completely. Here we study the electronic band structure of WTe$_2$ by quasiparticle interference with Scanning Tunneling Microscopy (STM) and observe, with the support of Density Functional Theory (DFT), the electron and hole bands around the Fermi level. We also report on the observation of Landau quantization in atomically resolved measurements and discuss the possible connection with band structure calculations.

cond-mat.mes-hall↗

arXiv2025

Gapless superconductivity from extremely dilute magnetic disorder in 2H-NbSe2-xSx

Most superconducting materials exhibit a vanishing density of states at the Fermi level and Anderson's theorem posits that the superconducting gap is robust against nonmagnetic disorder. Although dilute magnetic impurities lead to localized in-gap states, these states typically have no bearing on the material's bulk superconducting properties. However, numerous experiments reveal a finite density of states at the Fermi level in systems with an apparently negligible number of magnetic impurities. Here, using scanning tunneling microscopy and self-consistent Bogoliubov-de Gennes calculations, we find that gapless superconductivity emerges in 2H-NbSe2-xSx at remarkably low magnetic impurity concentrations. Furthermore, our density functional theory calculations and in-gap quasiparticle interference measurements demonstrate that the Se-S substitution significantly modifies the band structure. This modification favours nesting and dictates the in-gap scattering for x>0, in stark contrast to the dominant charge density wave interactions in pure 2H-NbSe2. Our findings reveal an unusual superconducting response to disorder and highlight the importance of incorporating material-specific band structures in the understanding of a superconductor's response to even very low concentrations of magnetic impurities.

cond-mat.supr-con↗

arXiv2025

Strain Engineering of Magnetoresistance and Magnetic Anisotropy in CrSBr

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 two-dimensional (2D) limit. Here, we demonstrate 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 ~10K. Our 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.

cond-mat.mtrl-sci↗