Showing 1–4 of 4 results for author: Saeed, U

Polarization Vortices in a Ferromagnetic Metal via Twistronics

Authors: Yingzhuo Lun, Xinxin Hu, Qi Ren, Umair Saeed, Kapil Gupta, Bernat Mundet, Ivan Pinto-Huguet, Jose Santiso, Jessica Padilla-Pantoja, Jose Manuel Caicedo Roque, Yunpeng Ma, Qian Li, Gang Tang, David Pesquera, Xueyun Wang, Jiawang Hong, Jordi Arbiol, Gustau Catalan

Abstract: 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… ▽ More 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. △ Less

Submitted 23 May, 2025; originally announced May 2025.

Comments: Manuscript(14 pages, 4 figures)+Supplementary Information

Beware of the water: Hidden hydrogenation of perovskite membranes made by the water-soluble sacrificial layer method

Authors: Umair Saeed, Felip Sandiumenge, Kumara Cordero-Edwards, Jessica Padilla-Pantoja, José Manuel Caicedo Roque, David Pesquera, José Santiso, Gustau Catalan

Abstract: The fabrication of perovskite oxide free-standing films (membranes) by lift-off methods using water-soluble sacrificial layers is appealing because of the new mechanical degrees of freedom that these membranes present over conventional epitaxial films. However, little is known about how their fabrication process, and in particular the exposure to water during the etching step, affects their proper… ▽ More The fabrication of perovskite oxide free-standing films (membranes) by lift-off methods using water-soluble sacrificial layers is appealing because of the new mechanical degrees of freedom that these membranes present over conventional epitaxial films. However, little is known about how their fabrication process, and in particular the exposure to water during the etching step, affects their properties. Here, we investigate how membranes of two perovskite archetypes, antiferroelectric PbZrO3 and paraelectric SrTiO3, are affected by water-based etching step. Using Raman spectroscopy and X-ray diffraction, we find evidence that hydrogen penetrates the perovskite structure. Concomitant with this protonation, the functional properties also change, and both materials display ferroelectric-like behavior that is absent in bulk ceramics or hydrogen-free films at room temperature. We also find that thermal annealing can be used to expel the hydrogen from the membranes, which henceforth recover bulk-like properties. The two main conclusions of this work are that (i) any perovskite membrane made by sacrificial layer hydrolysis is vulnerable to hydrogen penetration (protonation) that can induce important but extrinsic changes in functional properties, and (ii) the hydrogen can, and should, be expelled by annealing to recover intrinsic behaviour. △ Less

Submitted 2 May, 2025; v1 submitted 6 March, 2025; originally announced March 2025.

Comments: 21 pages, 5 figures, supplementary file included

Switching dynamics and improved efficiency of free-standing antiferroelectric capacitors

Authors: Umair Saeed, David Pesquera, Ying Liu, Ignasi Fina, Saptam Ganguly, Jose Santiso, Jessica Padilla, Jose Manuel Caicedo Roque, Xiaozhou Liao, Gustau Catalan

Abstract: 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, freestand… ▽ More 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. △ Less

Submitted 14 December, 2023; originally announced December 2023.

Comments: 27 pages, 7 Figures, Supplementary material

Photostrictive actuators based on freestanding ferroelectric membranes

Authors: Saptam Ganguly, David Pesquera, Daniel Moreno Garcia, Umair Saeed, Nona Mirzamohammadi, José Santiso, Jessica Padilla, José Manuel Caicedo Roque, Claire Laulhé, Felisa Berenguer, Luis Guillermo Villanueva, Gustau Catalan

Abstract: Complex oxides offer a wide range of functional properties, and recent advances in fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, we demonstrate photoactuation in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-stand… ▽ More Complex oxides offer a wide range of functional properties, and recent advances in fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, we demonstrate photoactuation in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent and holographic interferometry provide combined evidence for the photostrictive strain in BaTiO3 originating from partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated by light. △ Less

Submitted 24 March, 2024; v1 submitted 4 May, 2023; originally announced May 2023.