arXiv subjects

Jose Santiso

Publications and source records attributed to Jose Santiso.

9 recordsLinked to original sources

arXiv2026

Interface-resolved structural properties of epitaxial Y$_3$Fe$_5$O$_{12}$/ Gd$_3$Fe$_5$O$_{12}$ bilayers grown on GGG(111) by pulsed laser deposition

Epitaxial Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Fe$_5$O$_{12}$ (GdIG) thin films, along with their bilayer heterostructures, were grown on Gd$_3$Ga$_5$O$_{12}$(GGG)(111) substrates using pulsed laser deposition. Structural properties were investigated using X-ray diffraction, reciprocal space mapping, and cross-sectional transmission electron microscopy. The results confirm high crystalline quality and coherent epitaxial growth, with RSM revealing a coexistence of strained and partially relaxed regions governed by layer sequence. TEM analysis shows sharp interfaces, columnar microstructures, and antiphase boundaries that facilitate strain relaxation. A comparative study indicates that the GGG/YIG/GdIG stacking sequence exhibits improved structural quality with reduced defect density, attributed to the superior epitaxial growth of YIG on the substrate. These findings highlight the critical role of growth sequence in controlling strain and interfacial structure in garnet heterostructures.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced Photocurrent Response in Epitaxial 0.5PZT-0.5PFN Multiferroic Thin Films

The exploration of novel multiferroic materials with strong coupling between ferroelectric polarization and photovoltaic effects is crucial for next-generation optoelectronic devices. In this study, we characterized highly oriented 0.5Pb(Zr0.52Ti0.48)O3-0.5Pb(Fe0.5Nb0.5)O3 multiferroic thin films grown by pulsed laser deposition on SrTiO3 (001) substrates with a SrRuO3 bottom electrode. The films exhibited excellent crystalline quality, with a single perovskite phase and (001) orientation. They displayed good ferroelectric properties (remanent polarization $\sim$17 $\mu$C/cm$^2$, PUND; coercive field $\sim$150 kV/cm), alongside weak ferromagnetic behavior at room temperature (remanence 1.30 emu/cm$^3$; coercive field 90 Oe). Photovoltaic measurements demonstrated a robust, polarization-dependent photoresponse under 403 nm monochromatic laser illumination, achieving Jsc values between $\pm$20 $\mu$A/cm$^2$. This compelling observation confirms the intrinsic coupling between ferroelectric polarization and photovoltaic effects, highlighting the considerable promise of these single-phase multiferroic thin films for advanced photovoltaic and optoelectronic memory applications.

cond-mat.mtrl-sci↗

arXiv2026

Domain-induced control of latent heat in freestanding BaTiO$_3$ membranes

Thin ferroelectric BaTiO$_3$ films often exhibit continuous transitions instead of the first-order behavior of bulk crystals, a discrepancy usually attributed to epitaxial strain or dimensionality. Using quasi-adiabatic nanocalorimetry on freestanding BaTiO$_3$ membranes-free of clamping and substrate heat sinking-we show that domain morphology, not thickness or boundary conditions, controls the transition order. Thick membranes with large, monodomain-like regions display clear latent heat, whereas thinner membranes with dense 180$^{\circ}$ domain patterns show a continuous transition despite undergoing the same tetragonal-cubic structural change confirmed by x-ray diffraction. Piezoresponse force microscopy links this behavior to domain-size evolution, and a Ginzburg-Landau analysis demonstrates how reduced domain size lowers the free-energy barrier, rounding a nominally first-order instability. These results identify domain morphology as the key determinant of ferroelectric transition order in oxide membranes and establish design guidelines for enhancing caloric effects through domain engineering.

cond-mat.mtrl-sci↗

arXiv2025

Reconfigurable, Temperature Resilient Phase-Change Metasurfaces Fabricated via High Throughput Nanoimprinting Lithography

The combination of metasurfaces with chalcogenide phase-change materials is a highly promising route towards the development of multifunctional and reconfigurable nanophotonic devices. However, their transition into real-world devices is hindered by several technological challenges. This includes, amongst others, the lack of large area photonic architectures produced via scalable nanofabrication methods, as required for free-space photonic applications, along with the ability to withstand the high temperatures required for the phase-change process. In this work, we present a scalable nanofabrication strategy for the production of reconfigurable metasurfaces based on high-throughput, large-area nanoimprint lithography that is fully compatible with chalcogenide phase-change materials processing. Our approach involves the direct imprinting of high melting point, thermally stable TiO2 nanoparticle pastes, followed by the deposition of an Sb2Se3 thin film as the phase-change material active layer. The patterned titania film enables the creation of thermally robust metasurfaces, overcoming the limitations of conventional polymer-based nanoimprint approaches. The versatility of our approach is showcased by producing phase-change devices with two distinct functionalities: (i) metasurfaces with tunable spectral band switching and amplitude modulation capabilities across the near- to mid-infrared, and (ii) reconfigurable chiral metasurfaces, whose chiroptical activity can be switched between the visible and the near-infrared. Experimental results show excellent agreement with numerical simulations and reveal high uniformity across large areas.

physics.optics↗

arXiv2025

Polarization Vortices in a Ferromagnetic Metal via Twistronics

Recent advances in moire engineering provide new pathways for manipulating lattice distortions and electronic properties in low-dimensional materials. Here, we demonstrate that twisted stacking can induce dipolar vortices in metallic SrRuO3 membranes, despite the presence of free charges that would normally screen depolarizing fields and dipole-dipole interactions. These polarization vortices are correlated with moire-periodic flexoelectricity induced by shear strain gradients, and exhibit a pronounced dependence on the twist angle. In addition, multiferroic behavior emerges below the ferromagnetic Curie temperature of the films, whereby polarization and ferromagnetism coexist and compete, showing opposite twist-angle dependencies of their respective magnitudes. Density functional theory calculations provide insights into the microscopic origin of these observations. Our findings extend the scope of polarization topology design beyond dielectric materials and into metals.

cond-mat.mtrl-sci↗

arXiv2024

Coexistence of ferroelectric and ferrielectric phases in ultrathin antiferroelectric PbZrO3 thin films

Whereas ferroelectricity may vanish in ultra-thin ferroelectric films, it is expected to emerge in ultra-thin anti-ferroelectric films, sparking people's interest in using antiferroelectric materials as an alternative to ferroelectric ones for high-density data storage applications. Lead Zirconate (PbZrO3) is considered the prototype material for antiferroelectricity, and indeed previous studies indicated that nanoscale PbZrO3 films exhibit ferroelectricity. The understanding of such phenomena from the microstructure aspect is crucial but still lacking. In this study, we fabricated a PbZrO3 film with thicknesses varying from 5 nm to 80 nm. Using Piezoresponse Force Microscopy, we discovered the film displayed a transition from antiferroelectric behaviour in the thicker areas to ferroelectric behaviour in the thinner ones, with a critical thickness between 10 and 15 nm. In this critical thickness range, a 12 nm PZO thin film was chosen for further study using aberration-corrected scanning transmission electron microscopy. The investigation showed that the film comprises both ferroelectric and ferrielectric phases. The ferroelectric phase is characterized by polarisation along the pseudocubic [011] projection direction. The positions of Pb, Zr, and O were determined using the integrated differential phase contrast method. This allowed us to ascertain that the ferroelectric PbZrO3 unit cell is half the size of that in the antiferroelectric phase on the ab plane. The observed unit cell is different from the electric field-induced ferroelectric rhombohedral phases. Additionally, we identified a ferrielectric phase with a unique up-up-zero-zero dipole configuration. The finding is crucial for understanding the performance of ultrathin antiferroelectric thin films and the subsequent design and development of antiferroelectric devices.

cond-mat.mtrl-sci↗

arXiv2023

Switching dynamics and improved efficiency of free-standing antiferroelectric capacitors

We report the switching dynamics of antiferroelectric Lead Zirconate (PbZrO3) free standing capacitors compared to their epitaxial counterparts. Frequency dependence of hysteresis indicates that freestanding capacitors exhibit a lower dispersion of switching fields, lower residual polarization, and faster switching response as compared to epitaxially-clamped capacitors. As a consequence, freestanding capacitor membranes exhibit better energy storage density and efficiency.

cond-mat.mtrl-sci↗

arXiv2023

Native defect association in beta-Ga2O3 enables room-temperature p-type conductivity

The room temperature hole conductivity of the ultra wide bandgap semiconductor beta Ga2O3 is a pre-requisite for developing the next-generation electronic and optoelectronic devices based on this oxide. In this work, high-quality p-type beta-Ga2O3 thin films grown on r-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD) exhibit Rho = 50000Ohm.cm resistivity at room temperature. A low activation energy of conductivity as Ea2=170 meV was determined, associated to the oxygen - gallium native acceptor defect complex. Further, taking advantage of cation (Zn) doping, the conductivity of Ga2O3:Zn film was remarkably increased by three orders of magnitude, showing a long-time stable room-temperature hole conductivity with the conductivity activation energy of around 86 meV.

cond-mat.mtrl-sci↗

arXiv2020

Metallic Diluted Dimerization in VO2 Tweeds

The observation of electronic phase separation textures in vanadium dioxide (VO2), a prototypical electron-correlated oxide, has recently added new perspectives on the long standing debate about its metal-insulator transition and its applications. Yet, the lack of atomically-resolved information on phases accompanying such complex patterns still hinders a comprehensive understanding of the transition and its implementation in practical devices. In this work, atomic resolution imaging and spectroscopy unveils the existence of ferroelastic tweed structures on ~5 nm length scales, well below the resolution limit of currently employed spectroscopic imaging techniques. Moreover, density functional theory calculations show that such fine tweeds are formed by a metallic structure, formed by partially dimerized V-chains, that appears tetragonal (rutile) on average, but is locally monoclinic. These observations suggest that the metal/insulator coexistence among low-symmetry forms of VO2 is driven by lattice degrees of freedom, and provide a multiscale perspective for the interpretation of existing data, whereby phase coexistence and structural intermixing can occur all the way down to the atomic scale.

cond-mat.mtrl-sci↗