arXiv subjects

Jorge Íñiguez-González

Publications and source records attributed to Jorge Íñiguez-González.

At least 19 recordsLinked to original sources

arXiv2026

Computing at the Edge Enabled by Indoor Photovoltaics and Ferroelectrics

The exponential, pervasive rise of artificial intelligence (AI), hosted in large data centres, will test the limits of the underpinning infrastructure, including electricity and water supplies, which are becoming increasingly precious resources. Rather than performing all AI computations in centralized servers, for many functionalities, these can be performed locally across a network of billions of small, autonomous nodes, saving substantial energy costs associated with communication. This alternative paradigm is known as edge computing, or distributed intelligence (DI), but has been held back by the lack of availability of reliable local energy supplies matching the energy requirements of the computational infrastructure. Opportunities to address this challenge are emerging with rapid advances in high-performance indoor photovoltaics (IPVs) for local energy harvesting, as well as reductions in computational cost through neuromorphic or in-memory computing devices. In this perspective, we discuss the requirements of IPVs for DI, the extent to which emerging materials fulfil these requirements, and how current gaps could be addressed. We make the case that (anti)ferroelectric materials can surpass bottlenecks for both electrostatic energy storage and low-power in-memory neuromorphic computing. The core theme of this perspective is that co-creation between energy harvesting, storage and computing is essential for making DI a reliable and more sustainable alternative to centralized AI.

cond-mat.mtrl-sci↗

arXiv2026

Orientation engineering is a universal strategy for ferroelectric trans-switching

About two decades ago, ``strain engineering'' emerged as a powerful strategy to tune epitaxial thin films. Here we contend that ''orientation engineering'' - that is, controlling the film's growth direction - constitutes a complementary design route that opens unprecedented opportunities and deserves greater attention. Specifically, we show that orientation engineering can endow standard ferroelectric compounds with exotic and useful behaviors that may be difficult or impossible to obtain otherwise. Critically, we predict it readily enables ''trans-switching,'' where polarization components switch perpendicularly to the applied electric field, paving the way for novel 3D device architectures. We also show that, by controlling the electric screening provided by electrodes in contact with the film, ferrielectric behavior can be obtained. Notably, one can even design an operational mode where the switching is, in effect, fully transversal to the applied field. Supported by phenomenological calculations for representative compounds LiNbO$_3$ and BaTiO$_3$, we thus propose orientation engineering as a powerful and general method to unlock unprecedented functionalities in common ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2026

Intrinsic switching leads to oxygen diffusion and breakdown in hafnia ferroelectrics

Conventional ferroelectrics exhibit well-defined polarization states linked through electric switching. In fluorite-structured ferroelectrics like hafnia, though, switching and oxygen diffusion seem to coexist, enriching the nature of ferroelectricity. Here we address the intrinsic, room-temperature switching and diffusion kinetics of hafnia ferroelectrics using machine-learning molecular dynamics. We identify two distinct switching mechanisms that are both active at realistic time scales. Critically, our simulations reveal that, because the lattice does not dissipate fast enough the heat originating from localized switching events, these two processes concatenate in an avalanche-like manner leading to oxygen conduction. Our results thus show that intrinsic switching leads to breakdown in hafnia ferroelectrics. They also suggest how this outcome might be avoided through suitably designed field pulses.

cond-mat.mtrl-sci↗

arXiv2026

Harnessing electrostatics through temperature modulations to control ferroelectrics

Temperature modulations provide an alternative method for dynamically controlling the ferroelectric state. In this paper, we use scale-independent Landau potentials and predictive atomistic simulations to explore how temperature modulation can harness the depolarizing field to obtain non-electrical poling. We further predict that temperature gradients can be combined with strain to induce persistent polar textures such as multidomain states.

cond-mat.mtrl-sci↗

arXiv2026

Alternative origins of polarity in compressively strained SrTiO3-RENiO3 capacitors

Since its original prediction 25 years ago, room-temperature out-of-plane ferroelectricity in compressively strained SrTiO3 remains an ongoing pursuit. In this work, we investigate the structural, electrical and electromechanical properties of highly strained epitaxial SrTiO3 capacitors with rare earth nickelate electrodes. The SrTiO3 layers experience compressive strains up to -3% and exhibit pronounced tetragonality, comparable to that of bulk PbTiO3. Variable-temperature electrical measurements and room-temperature piezoresponse force microscopy reveal butterfly-shaped capacitance-voltage hysteresis and domain-like electromechanical response typical of ferroelectric materials. However, the overall behavior is inconsistent with a stable ferroelectric state. We therefore propose an alternative mechanism for the observed polarity in our samples based on spatially inhomogeneous internal fields. Our first-principles calculations show that such fields may arise from charge discontinuities between the formally charged NdNiO3 layers and charge-neutral SrTiO3 layers.

cond-mat.mtrl-sci↗

arXiv2026

A GPU-based Solver for Polarization Dynamics in Ferroelectric Materials

Ferroelectric materials can be used for the development of multiple device concepts combining non-volatility, small dimensions, low-power actuation, and electrical tunability. Such development demands efficient and precise design of simulation tools describing the polarization texture. However, most existing ferroelectric solvers are CPU-based and rely on simplified electrostatic treatments and reduced-dimensional representations of the polarization field. These approximations limit their ability to capture finite-size and boundary effects and restrict the range of domain structures and domain walls that can be realistically simulated. Here, we present a fully GPU (graphics processing units)-accelerated and scalable numerical solver, named PETASPIN_microelectrics, for computing the full polarization vector field of ferroelectric systems using the Ginzburg-Landau formalism. Our solver incorporates an optimized and validated calculation of the full electrostatic field and enables the parallel execution of multiple simulations. We systematically validated the solver with several benchmark problems, including phase transitions in BaTiO3 and ferroelectric domain wall profiles. Our simulations reproduce temperature-driven hysteretic phase transitions in BaTiO3. We also reproduce hysteresis loops and demonstrate stabilization of a three-dimensional hybrid skyrmion in a PbTiO3/SrTiO3 bilayer system. Our results show quantitative agreement with predictions from an analytical theory and prior experimental studies. The proposed solver provides an efficient, accurate platform for large-scale simulations of ferroelectric materials including stabilization of topological textures supporting predictive modeling for next-generation of ferroelectric device design.

cond-mat.mtrl-sci↗

arXiv2026

Effective dynamic constants for nonequilibrium third-principles simulations

Computational studies of the thermodynamic properties of materials at the mesoscopic and macroscopic scales -- involving lengths and times of at least $μ$m and $μ$s, respectively -- rely on a coarse-graining approximation such that only a few relevant collective variables are treated explicitly. Those variables typically take the form of fields defined everywhere in space or macroscopic quantities when spatial inhomogeneities can be treated implicitly. The free energy is usually expressed as a Landau-like potential whose temperature-dependent minima track stable states, characteristic equilibrium fluctuations being implicitly accounted for. Further, the response of the system to external perturbations, and its relaxation toward thermal equilibrium, are described in terms of simple equations of motion governed by effective inertial and viscous-damping constants. There is considerable literature on the problem of deriving Landau free energy potentials, from either experiment or predictive atomistic simulations, including recent efforts to develop systematic machine-learning approaches that we denote ``third principles''. Much less attention has received the calculation of the effective constants controlling the nonequilibrium macroscopic or mesoscopic dynamics. Here we tackle that problem, describing a protocol that allows us to compute the temperature-dependent inertial and damping coefficients associated to the electric polarization in representative soft-mode ferroelectric PbTiO$_{3}$. Our scheme lends itself to a widespread application, although the non-trivial behaviors found in PbTiO$_{3}$ suggest that more case studies will be needed to finetune a general and robust calculation protocol. Our results also allow us to comment on common assumptions in the literature of effective dynamic treatments of ferroelectrics and related materials.

cond-mat.mtrl-sci↗

arXiv2026

A family tree for hafnia

Several candidate reference phases have been proposed to discuss phase transitions and ferroelectricity in hafnia in recent years. Although these proposals comply with crystallographic requirements, a physically compelling rationale connecting parent and daughter phases is often lacking. This problem is aggravated by the absence of clearly dominant polarization switching pathways, making it difficult to formulate a robust physical criterion for identifying the relevant high-symmetry states. Here we use first-principles calculations to show that pressure provides a simple and robust criterion for establishing physically meaningful family relationships among many hafnia polymorphs, including the monoclinic ground state and the technologically relevant ferroelectric phase, and their respective parent structures. Our simulations also reveal several previously unreported phases, including higher-energy structures that act as common ancestors of the widely discussed cubic and orthorhombic reference phases.

cond-mat.mtrl-sci↗

arXiv2025

Minimalist machine-learned interatomic potentials can predict complex structural behaviors accurately

The past decade has witnessed a spectacular development of machine-learned interatomic potentials (MLIPs), to the extent that they are already the approach of choice for most atomistic simulation studies not requiring an explicit treatment of electrons. Typical MLIP usage guidelines emphasize the need for exhaustive training sets and warn against applying the models to situations not considered in the corresponding training space. This restricts the scope of MLIPs to interpolative calculations, essentially denying the possibility of using them to discover new phenomena in a serendipitous way. While there are reasons to be cautious, here we adopt a more sanguine view and challenge the predictive power of two representative and widely available MLIP approaches. We work with minimalist training sets that rely on little prior knowledge of the investigated materials. We show that the resulting models -- for which we adopt modest/default choices of the defining hyperparameters -- are very successful in predicting non-trivial structural effects (competing polymorphs, energy barriers for structural transformations, occurrence of non-trivial topologies) in a way that is qualitatively and quasi-quantitatively correct. Our results thus suggest an expanded scope of modern MLIP approaches, evidencing that somewhat trivial -- and easy to compute -- models can be an effective tool for the discovery of novel and complex physical phenomena.

cond-mat.mtrl-sci↗

arXiv2025

Chiral soft mode transition driven by strain in ferroelectric bubble domains

Chirality in solids is attracting growing attention as a potential ferroic order, yet virtually no paradigmatic example of a soft-mode achiral-to-chiral phase transition has been firmly established to date. Here we identify ferroelectric bubble domains as a model system that undergoes a strain-driven achiral-to-chiral transition exhibiting the hallmarks of spontaneous symmetry breaking. Using second-principles atomistic simulations, we uncover chiral phonon modes in ferroelectric/dielectric superlattices that soften under epitaxial strain following textbook soft-mode behaviour. The transition is accompanied by a change in topological character, highlighting an interplay between chirality and topology in these systems. This work provides a concrete step towards establishing chirality as a genuine ferroic order in solids.

cond-mat.mtrl-sci↗

arXiv2025

Extrinsic nature of the polarization in hafnia ferroelectrics

Hafnia and related fluorites defy our understanding of ferroelectricity, even if we restrict ourselves to the intrinsic properties of ideal crystals. Here we focus on a critical puzzle, namely, the sign of the electric polarization. Using first-principles simulations, we show that a polar hafnia layer with a fixed atomic configuration can give rise to depolarizing fields of either positive or negative sign, depending on the environment. This implies that (the sign of) the polarization in hafnia is extrinsic in nature. We explain this result and discuss its relevance to other ferroelectric families.

cond-mat.mtrl-sci↗

arXiv2025

Machine learning Landau free energy potentials

We show how to construct Landau-like free energy potentials using a machine-learning approach. For concreteness, we focus on perovskite oxide PbTiO$_{3}$. We work with a training set obtained from Monte Carlo simulations based on an atomistic ''second-principles'' potential for PbTiO$_{3}$. We rely exclusively on data that would be experimentally accessible -- i.e., temperature-dependent polarization and strain, both with and without external electric fields and stresses applied --, to explore scenarios where the training set could be obtained from laboratory measurements. We introduce a scheme that allows us to identify optimal polynomial models of the temperature-dependent free energy surface, mapped as a function of the homogeneous electric polarization and homogeneous strain. Our results for PbTiO$_{3}$ show that a very simple polynomial -- where only two parameters depend linearly on temperature -- is sufficient to yield a correct description of the material's behavior. Remarkably, the obtained models also capture the subtle couplings by which elastic strain controls key features of ferroelectricity in PbTiO$_{3}$ -- i.e., the symmetry of the polar phase and the discontinuous character of the transition --, despite the fact that no effort was made to include such information in the training set. We emphasize the distinctive aspects of our methodology (which relies on an original form of validation step) by comparing it with the usual machine-learning approach for model construction. Our results illustrate how physically motivated models can have remarkable predictive power, even if they are derived from a limited amount of data. We argue that such ''third-principles'' models can be the basis for predictive macroscopic or mesoscopic simulations of ferroelectrics and other materials undergoing non-reconstructive structural transitions.

cond-mat.mtrl-sci↗

arXiv2025

First principles study of [111]-oriented epitaxially strained Rare-Earth Nickelate NdNiO$_3$

Density functional theory is used to investigate the effect of biaxial strain on the structural, electronic and magnetic properties of [111]-oriented NdNiO$_3$, as a representative of the rare-earth perovskites that undergo metal-to-insulator transitions. We find that this constraint on the system induces unique structural phase transitions not previously observed under the well-studied bulk or [001]-oriented strained systems. We also report unique electronic behaviour, including amplification of the electronic band-gap with tensile strain, and insulating, charge-ordered phases with non-orthorhombic tilt patterns. To provide clarity to the trends we observe, we also investigate the coupling between the breathing mode and strain, where we observe certain strains to directly favour and disfavour the creation of the breathing mode (and thus the associated charge-ordering). The amplification of the band gap with strain is understood in terms of a cooperative coupling between the elastic constraint and octahedral breathing, which expands on the previously reported triggered mechanism mediated by octahedral tilting.

cond-mat.mtrl-sci↗

arXiv2025

Guidelines for the optimization of hafnia-based ferroelectrics through superlattice engineering

Hafnia-based ferroelectrics are revolutionizing the data storage industry and the field of ferroelectrics, with improved materials and devices being reported monthly. However, full understanding and control has not been reached yet and the ideal material still needs to be found. Here we report ferroelectric hafnia-zirconia superlattices made out of zirconium-substituted hafnia (Hf$_{1-x}$Zr$_x$O$_2$) sublayers of varying stoichiometries alternating with pure ZrO$_2$ sublayers. It is observed that the ZrO$_2$ layers in these superlattices act as a booster for the total remnant polarization (P$_r$). By combining the benefits of the ZrO$_2$ layers and the added interfaces, which help prevent breakdown, we fabricate superlattices with a total 87.5% ZrO$_2$ content, exhibiting record polarizations with a 2P$_r$ value of 84 $μ$C/cm$^2$ that can be cycled 10$^9$ times, while maintaining a 2P$_r$ > 20 $μ$C/cm$^2$. Next to these attractive properties, substitution of HfO$_2$ by the much more abundant ZrO$_2$ offers a significant step towards the sustainable application of these devices.

cond-mat.mtrl-sci↗

arXiv2025

Hybrid antiferroelectric-ferroelectric domain walls in noncollinear antipolar oxides

Antiferroelectrics are emerging as advanced functional materials and are fertile ground for unusual electric effects. For example, they enhance the recoverable energy density in energy storage applications and give rise to large electromechanical responses. Here, we demonstrate noncollinearity in dipolar order as an additional degree of freedom, unlocking physical properties that are symmetry-forbidden in classical antiferroelectrics. We show that noncollinear order of electric dipole moments in K$_3$[Nb$_3$O$_6$|(BO$_3$)$_2$] leads to a coexistence of antiferroelectric and ferroelectric behaviors. Besides the double-hysteresis loop observed in antiferroelectrics, a pronounced piezoresponse and electrically switchable domains are observed, separated by atomically sharp and micrometer-long charged domain walls. Hybrid antiferroelectric-ferroelectric responses are expected in a wide range of noncollinear systems, giving a new dimension to the research on antiferroelectrics and multifunctional oxides in general.

cond-mat.mtrl-sci↗

arXiv2025

Prediction of Room Temperature Electric Field Reversal of Magnetization in the Family of $A_4B_3\rm{O}_9$ Layered Oxides

The promise of a strong magnetoelectric coupling in a multiferroic material is not only of fundamental interest, but also forms the basis of next generation memory devices where the direction of magnetization can be reversed by an external electric field. Using group-theory led first-principles calculations, we have identified a hitherto unknown polar phase of the $A_4B_3\rm{O}_9$ layered oxides, where the polar mode couples to the magnetic modes through a rare $Γ$-point magnetoelectric-multiferroic coupling scheme such that the net magnetization can be directly reversed by an electric field switching of the polar mode. Furthermore, in agreement with previous experimental observations, we predict room temperature magnetism in $A_4B_3\rm{O}_9$ oxides which indicates the promising practical applications of these compounds in the next generation memory devices.

cond-mat.mtrl-sci↗

arXiv2025

Giant energy density nitride dielectrics enabled by a paraelectric-metaparaelectric phase transition

Electrostatic dielectric capacitors are foundational to advance the electronics and electric power devices due to their ultrafast charging/discharging capability and high-power density. However, the low energy density limits the potential for next generation devices in terms of miniaturization and integration. We propose a strategy that relies on inducing a field-driven phase transition that we denote paraelectric-metaparaelectric, which yields an ultrahigh energy density in III-nitrides. III-nitride compounds (Al, Sc, B)N with certain cation concentrations possess a nonpolar hexagonal ground phase which could transform into a polar wurtzite phase under a very large electric field, which is denoted as metaparaelectric with nearly null hysteresis P-E loop. This paraelectric-metaparaelectric transition leads to a polarization saturation at large electric field. The corresponding P-E loop displays a giant energy density of 308 J/cm$^3$ with high efficiency nearly 100%. The proposed paraelectric-metaparaelectric phase transition strategy in nitrides opens an avenue to design of next generation high performance dielectrics.

cond-mat.mtrl-sci↗

arXiv2025

Magnon thermal conductivity in multiferroics with spin cycloids

Multiferroic materials, characterized by the occurrence of two or more ferroic properties, hold potential in future technological applications and also exhibit intriguing phenomena caused by the interplay of multiple orders. One such example is the formation of spin cycloid structures within multiferroic materials, which we investigate in this work by focusing on their magnon excitations and transport based on a general multiferroic Hamiltonian with an antiferromagnetic order. More specifically, we identify the ground state and explore the dynamics of magnon modes, revealing distinct in-plane and out-of-plane modes with anisotropic dispersion relations.The magnon modes include a massless excitation, known as the Goldstone boson, originating from the spontaneous breaking of the translational symmetry by the formation of the cycloid structures. By employing the Boltzmann transport formalism, the magnonic thermal conductivity with spin cycloids and low-temperature anisotropic behaviors is discussed. This work provides pathways to envision the spin-textured multiferroics, which may serve as a fertile ground to look for novel thermal and spin transport with the rich interplay of quasiparticles such as magnons and phonons.

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