arXiv subjects

Nini Pryds

Publications and source records attributed to Nini Pryds.

At least 19 recordsLinked to original sources

arXiv2026

Thickness-dependent crack suppression and wrinkle formation in freestanding BaTiO3 membranes

Freestanding ferroelectric oxide membranes offer a promising route toward silicon-integrated low-power electronic and memory devices, but reproducible membrane quality remains challenging, particularly in ultrathin BaTiO3 (BTO), where cracking and wrinkling hinder integration. Here, we show that crack and wrinkle formation in released BaTiO3 membranes can be tuned by jointly controlling oxide thickness and polymer support thickness. Reducing the BaTiO3 thickness from 15 nm to 5 nm suppresses large-area, optically visible cracking across the analysed regions, but promotes dense nanoscale wrinkling, revealing a trade-off between fracture mitigation and morphological instability. In 10 nm BaTiO3 membranes, polymer support thickness further modulates wrinkling, with an intermediate thickness reducing wrinkle density. Piezoresponse force microscopy reveals time-dependent evolution of written contrast after release, indicating that apparent ferroelectric response is influenced by polarization switching, post-release morphology, interfacial contact, charge screening, and strain relaxation. These results establish processing guidelines for integrating freestanding ferroelectrics into future devices.

cond-mat.mtrl-sci↗

arXiv2026

Designing dislocation-driven polar vortex networks in twisted perovskites

Twisting two atomic layers produces a geometric moire pattern, but bonding-induced interfacial reconstruction fundamentally transforms this into an ordered dislocation network - a distinction obscured in weakly-bonded van der Waals systems. Although in-plane topological vortex nanostructures arising from twisting-induced lateral strain modulation have been linked to periodic moire patterns in freestanding perovskite layers and 2D bilayers, their coupling to the interfacial dislocation network in twisted layers remains unresolved. Here we demonstrate that twisting freestanding SrTiO3 layers undergo interfacial reconstruction into a network of screw dislocations, accompanied by the emergence of in-plane topological vortices. Unlike in previous reports, these vortices are associated with the periodicity of the dislocation network rather than with geometric moire patterns. Four-dimensional scanning transmission electron microscopy (4D-STEM) reveals long-range ordered vortex-antivortex arrays with nearly continuous polarisation rotation. A machine-learning interatomic potential, trained on first-principles calculations, together with phase-field modelling, confirms that competing strains within the dislocation network stabilize polar vortex-antivortex pairs and drive the emergence of an electronic superlattice with a well-defined periodicity. Our results establish twist-controlled dislocation networks as a new and versatile route to designing local polar and electronic structures in oxide materials.

cond-mat.mtrl-sci↗

arXiv2026

Instability-driven mechanically locked states in functional oxide membranes

Mechanical instabilities in thin solids offer a powerful route to engineer nonlinear responses, yet their controlled use in functional crystalline oxides has remained largely unexplored. Notably, by changing the aspect ratio of solids, the energy landscape around equilibrium can be modified to induce non-linearities under lateral stresses through non-lateral deformations. These nonlinear systems can develop multiple local energy minima where the system can settle and switch between states through the application of a driving force. Crucially, recent advances in oxide thin film growth have enabled the fabrication of freestanding oxide membranes, paving a viable path for their use in bistable architecture, particularly at the nanoscale. Here, we demonstrate that freestanding oxide membranes, such as SrTiO3 (STO) and BaTiO3 (BTO), relax into well-defined metastable buckling states when transferred onto lithographically defined cavities. The membrane deformation is determined by the interplay between built-in residual strain, bending stiffness, and cavity geometry, resulting in reproducible bistable states with distinct strain distributions. Using a combination of atomic force microscopy, in-contact Kelvin probe measurements, and finite-element modelling, we reveal that these mechanically locked states directly shape the electromechanical potential landscape of ferroelectric BaTiO3. We further demonstrate reversible snapthrough transitions between mechanically degenerate states, establishing complex oxides as deterministic, geometry-tunable building blocks for nonlinear nanoelectromechanical architectures. Our results illustrate a general strategy for exploiting mechanical instabilities to encode and manipulate functional responses in ultrathin crystalline membranes.

cond-mat.mtrl-sci↗

arXiv2026

Intrinsic Negative-U Centers in Freestanding LaAlO3/SrTiO3 Micro-membranes

The LaAlO3/SrTiO3 (LAO/STO) interface hosts a rich range of electronic phenomena, including unconventional electron pairing that in quantum dots gives rise to a negative effective charging energy U. Here, we show freestanding LAO/STO micro-membranes naturally hosting negative-U centers, where lateral confinement arises intrinsically, rather than from engineered nanostructures. These centers coexist with gate-tunable superconductivity and can remain stable upon thermal cycling from millikelvin temperatures to room temperature. Transport is in excellent agreement with calculations based on a negative-U Anderson model, and electrostatic simulations indicate characteristic center sizes of 20-80 nm. Our findings suggest that negative-U centers may arise from the intrinsic interfacial inhomogeneity typical of LAO/STO, and should therefore be considered a general feature of the LAO/STO interface. This could have important consequences for the microwave response of interfacial superconducting devices.

cond-mat.mtrl-sci↗

arXiv2025

Ultrathin oxide freestanding membranes with large-scale continuity and structural perfection

Freestanding oxide membranes offer integration with advanced semiconductor platforms, unlocking opportunities for flexible electronics, silicon-based spintronics, neuromorphic computing, and high-performance energy technologies. Scalable fabrication of such membranes is essential for bridging fundamental discoveries in complex oxides with practical device deployment. However, the lateral dimensions of crack- and wrinkle-free membranes remain limited to millimeter scales, forming a critical bottleneck for large-area architectures. Overcoming this challenge demands strategies that preserve crystalline quality while suppressing defect transfer during release. Here, we demonstrate an approach based on a water-soluble sacrificial layer of super-tetragonal Sr4Al2O7, enabling the fabrication of ultrathin, crack-free, and wrinkle-free free-standing oxide membranes spanning centimeter-scale areas. This method is broadly applicable to a wide range of oxides and establishes a new pathway toward large-scale silicon integration and flexible oxide technologies. Nevertheless, dissolution of the sacrificial layer introduces oxygen vacancies into the SrRuO3 membranes, with diffusion depths reaching six unit cells, leading to anomalous "up-and-down" transport behavior. Although post-annealing can eliminate these vacancies, the required temperatures are incompatible with CMOS processes. Therefore, ultrathin freestanding membranes fabricated by water-assisted lift-off still face critical challenges for integration into miniaturized silicon-based oxide devices.

cond-mat.mtrl-sci↗

arXiv2025

Metal-organic Pulsed Laser Deposition for Complex Oxide Heterostructures

Point defects in complex oxide thin films play a critical role in determining material properties but remain challenging to control with precision. This study introduces metal-organic pulsed laser deposition (MOPLD) as a novel synthesis technique for the precise manipulation of these defects, using LaAlO3/SrTiO3 (LAO/STO) as a model system. By employing titanium tetraisopropoxide (TTIP) as the titanium precursor, MOPLD achieves refined stoichiometric control in STO layers while preserving their structural integrity, as confirmed by X-ray diffraction and Raman spectroscopy. Depth-resolved cathodoluminescence spectroscopy and density functional theory calculations reveal that increasing TTIP flux during STO growth enhances the [TiSr]/[VSr] ratio and reduces the [VO] concentration. These defect modifications lead to a significant improvement in the low-temperature mobility of the two-dimensional electron gas at the LAO/STO interface, evidenced by distinct Shubnikov-de Haas oscillations. This work underscores the potential of MOPLD to advance defect engineering in complex oxide heterostructures, opening new avenues for quantum material research.

cond-mat.mtrl-sci↗

arXiv2024

Improving Electrical Contact Quality and Extraordinary Magnetoresistance in High Mobility III-V Semiconductors

Magnetometers based on the extraordinary magnetoresistance (EMR) effect are promising for applications which demand high sensitivity combined with room temperature operation but their application for magnetic field sensing requires further optimization. A key challenge is to obtain Ohmic metal/semiconductor contacts with low contact resistances in EMR devices comprising semiconductors with low carrier densities and high electron mobilities, yet, this topic remains scarcely investigated experimentally. By annealing high-mobility InSb in argon with systematically increasing temperatures, we experimentally demonstrate how the contact resistance to InSb films can be improved by two orders of magnitude by annealing to the micro-Ohm cm2 range without degrading the high mobility. We further show that lowering the contact resistance monotonously increases the room temperature magnetoresistance at 2 T from 700% to 65,000%. Lastly, we explore the origin of intrinsic magnetoresistance in high-mobility InSb thin films and suggest that it can best be explained by multiple band conduction.

physics.app-ph↗

arXiv2024

Electron-vacancy scattering in SrNbO$_3$ and SrTiO$_3$: A DFT-NEGF study

Oxygen vacancies are often attributed to changes in the electronic transport for perovskite oxide materials (ABO$_3$). Here, we use density functional theory (DFT) coupled with non-equilibrium Green's functions (NEGF) to systematically investigate the influence of O vacancies and also A and B-site vacancies, on the electronic transport as characterised by a scattering cross-section. We consider SrNbO$_3$ and n-type SrTiO$_3$ and contrast results for bulk and thin film (slab) geometries. By varying the electron doping in SrTiO$_3$ we get insight into how the electron-vacancy scattering vary for different experimental conditions. We observe a significant increase in the scattering cross-section (in units of square-lattice parameter, $a^2$) from ca. $0.5-2.5a^2$ per vacancy in SrNbO$_3$ and heavily doped SrTiO$_3$ to more than $9a^2$ in SrTiO$_3$ with 0.02 free carriers per unit cell. Furthermore, the scattering strength of O vacancies is enhanced in TiO$_2$ terminated surfaces by more than 6 times in lowly doped SrTiO$_3$ compared to other locations in slabs and bulk systems. Interestingly, we also find that Sr vacancies go from being negligible scattering centers in SrNbO$_3$ and heavily doped SrTiO$_3$, to having a large scattering cross-section in weakly doped SrTiO$_3$. We therefore conclude that the electron-vacancy scattering in these systems is sensitive to the combination of electron concentration and vacancy location.

cond-mat.mtrl-sci↗

arXiv2023

Provoking topology by octahedral tilting in strained SrNbO$_3$

Transition metal oxides with a wide variety of electronic and magnetic properties offer an extraordinary possibility to be a platform for developing future electronics based on unconventional quantum phenomena, for instance, the topology. The formation of topologically non-trivial states is related to crystalline symmetry, spin-orbit coupling, and magnetic ordering. Here, we demonstrate how lattice distortions and octahedral rotation in SrNbO$_3$ films induce the band topology. By employing angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we verify the presence of in-phase $a^0a^0c^+$ octahedral rotation in ultra-thin SrNbO$_3$ films, which causes the formation of topologically-protected Dirac band crossings. Our study illustrates that octahedral engineering can be effectively exploited for implanting and controlling quantum topological phases in transition metal oxides.

cond-mat.mtrl-sci↗

arXiv2023

Octahedral distortions in SrNbO$_3$: Unraveling the structure-property relation

Strontium niobate has triggered a lot of interest as a transparent conductor and as a possible realization of a correlated Dirac semi-metal. Using the lattice parameters as a tunable knob, the energy landscape of octahedral tilting was mapped using density functional theory calculations. We find that biaxial compressive strain induces tilting around the out-of-plane axis, while tensile strain induces tilting around the two in-plane axes. The two competing distorted structures for compressive strain show semi-Dirac dispersions above the Fermi level in their electronic structure. Our density functional theory calculations combined with dynamical mean field theory (DFT+DMFT) reveals that dynamical correlations downshift these semi-Dirac like cones towards the Fermi energy. More generally, our study reveals that the competition between the in-phase and out-of-phase tilting in SrNbO$_3$ provides a new degree of freedom which allows for tuning the thermoelectric and optical properties. We show how the tilt angle and mode is reflected in the behavior of the Seebeck coefficient and the plasma frequency, due to changes in the band structure.

cond-mat.mtrl-sci↗

arXiv2022

Reconstruction of low dimensional electronic states by altering the chemical arrangement at the SrTiO3 surface

Developing reliable methods for modulating the electronic structure of the two-dimensional electron gas (2DEG) in SrTiO3 is crucial for utilizing its full potential and inducing novel properties. Here, we show that relatively simple surface preparation reconstructs the 2DEG of SrTiO3 (STO) surface, leading to a Lifshitz-like transition. Combining experimental methods, such as angle-resolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy (XPS) with ab initio calculations, we find that the modulation of the surface band structures is primarily attributed to the reorganization of the chemical composition. In addition, ARPES experiments demonstrate that vacuum ultraviolet (VUV) light can be efficiently employed to alter the band renormalization of the 2DEG system and control the electron-phonon interaction (EPI). Our study provides a robust and straightforward route to stabilize and tune the low-dimensional electronic structure via the chemical degeneracy of the STO surface.

cond-mat.str-el↗

arXiv2022

Current Mapping of Amorphous LaAlO3/SrTiO3 near the Metal-Insulator Transition

The two-dimensional electron system found between LaAlO3 and SrTiO3 hosts a variety of physical phenomena that can be tuned through external stimuli. This allows for electronic devices controlling magnetism, spin-orbit coupling, and superconductivity. Controlling the electron density by varying donor concentrations and using electrostatic gating are convenient handles to modify the electronic properties, but the impact on the microscopic scale, particularly of the former, remains underexplored. Here, we image the current distribution at 4.2 K in amorphous-LaAlO3/SrTiO3 using scanning superconducting-quantum-interference-device microscopy while changing the carrier density in situ using electrostatic gating and oxygen annealing. We show how potential disorder affects the current and how homogeneous 2D flow evolves into several parallel conducting channels when approaching the metal-to-insulator transition. We link this to ferroelastic domains and oxygen vacancies. This has important consequences for micro- and nanoscale devices with low carrier density and fundamental studies on quantum effects in oxides.

cond-mat.mtrl-sci↗

arXiv2021

Band-Order Anomaly at the γ-Al2O3/SrTiO3 Interface Drives the Electron-Mobility Boost

Rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about two orders of magnitude has been demonstrated at the spinel/perovskite γ-Al2O3/SrTiO3 interface compared to the paradigm perovskite/perovskite LaAlO3/SrTiO3. We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in γ-Al2O3/SrTiO3 which depopulates electron states in the top STO layer. This rearrangement of the mobile electron system pushes the electron density away from the interface that reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel γ-Al2O3 and perovskite SrTiO3. The band-order engineering exploiting the fundamental symmetry properties emerges as another route to boost the performance of oxide devices.

cond-mat.mtrl-sci↗

arXiv2021

Time-reversal symmetry breaking driven topological phase transition in EuB$_6$

The interplay between time-reversal symmetry (TRS) and band topology plays a crucial role in topological states of quantum matter. In time-reversal-invariant (TRI) systems, the inversion of spin-degenerate bands with opposite parity leads to nontrivial topological states, such as topological insulators and Dirac semimetals. When the TRS is broken, the exchange field induces spin splitting of the bands. The inversion of a pair of spin-splitting subbands can generate more exotic topological states, such as quantum anomalous Hall insulators and magnetic Weyl semimetals. So far, such topological phase transitions driven by the TRS breaking have not been visualized. In this work, using angle-resolved photoemission spectroscopy, we have demonstrated that the TRS breaking induces a band inversion of a pair of spin-splitting subbands at the TRI points of Brillouin zone in EuB$_6$, when a long-range ferromagnetic order is developed. The dramatic changes in the electronic structure result in a topological phase transition from a TRI ordinary insulator state to a TRS-broken topological semimetal (TSM) state. Remarkably, the magnetic TSM state has an ideal electronic structure, in which the band crossings are located at the Fermi level without any interference from other bands. Our findings not only reveal the topological phase transition driven by the TRS breaking, but also provide an excellent platform to explore novel physical behavior in the magnetic topological states of quantum matter.

cond-mat.mtrl-sci↗

arXiv2021

Atomic-scale insights into electro-steric substitutional chemistry of cerium oxide

Cerium oxide (ceria, CeO2) is one of the most promising mixed ionic and electronic conducting materials. Previous atomistic analysis has covered widely the effects of substitution on oxygen vacancy migration. However, an in-depth analysis of the role of cation substitution beyond trivalent cations has rarely been explored. Here, we investigate soluble monovalent, divalent, trivalent and tetravalent cation substituents. By combining classical simulations and quantum mechanical calculations, we provide an insight into defect association energies between substituent cations and oxygen vacancies as well as their effects on the diffusion mechanisms. Our simulations indicate that oxygen ionic diffusivity of subvalent cation-substituted systems follows the order Gd>Ca>Na. With the same charge, a larger size mismatch with Ce cation yields a lower oxygen ionic diffusivity, i.e., Na>K, Ca>Ni, Gd>Al. Based on these trends, we identify species that could tune the oxygen ionic diffusivity: we estimate that the optimum oxygen vacancy concentration for achieving fast oxygen ionic transport is 2.5% for GdxCe1-xO2-x/2, CaxCe1-xO2-x and NaxCe1-xO2-3x/2 at 800 K. Remarkably, such a concentration is not constant and shifts gradually to higher values as the temperature is increased. We find that co-substitutions can enhance the impact of the single substitutions beyond that expected by their simple addition. Furthermore, we identify preferential oxygen ion migration pathways, which illustrate the electro-steric effects of substituent cations in determining the energy barrier of oxygen ion migration. Such fundamental insights into the factors that govern the oxygen diffusion coefficient and migration energy would enable design criteria to be defined for tuning the ionic properties of the material, e.g., by co-doping.

cond-mat.mtrl-sci↗

arXiv2019

Gate-tunable Rashba spin-orbit coupling and spin polarization at diluted oxide interfaces

Diluted oxide interface of LaAl1-xMnxO/SrTiO3 (LAMO/STO) provides a new way of tuning the ground states of the interface between the two band insulators of LAO and STO from metallic/superconducting to highly insulating. Increasing the Mn doping level (x) leads to a delicate control of the carrier density as well as a raise in the electron mobility and spin polarization. Herein, we demonstrate a tunable Rashba spin-orbit coupling (SOC) and spin polarization of LAMO/STO (0.2 <= x <= 0.3) by applying a back gate. The presence of SOC causes the splitting of energy band into two branches by a spin splitting energy. The maximum spin splitting energy depends on the Mn doping and decreases with the increasing Mn content and then vanishes at x = 0.3. The carrier density dependence of the spin splitting energy for different compositions shows a dome-shaped behavior with a maximum at different normalized carrier density. These findings have not yet been observed in LAO/STO interfaces. A fully back-gate-tunable spin-polarized 2DEL is observed at the interface with x = 0.3 where only dxy orbits are populated (5.3E12 cm-2 <= ns <= 1.0E13 cm-2). The present results shed light on unexplored territory in SOC at STO-base oxide heterostructures and make LAMO/STO an intriguing platform for spin-related phenomena in 3d-electron systems.

cond-mat.str-el↗

arXiv2019

On the emergence of conductivity at SrTiO3-based oxide interfaces -- an in-situ study

Heterostructures and crystal interfaces play a major role in state-of-the-art semiconductor devices and play a central role in the field of oxide electronics. In oxides the link between the microscopic properties of the interfaces and bulk properties of the resulting heterostructures challenge our fundamental understanding. Insights on the early growth stage of interfaces and its influence on resulting physical properties are scarce -- typically the information is inferred from post growth characterization. Here, we report on real time measurements of the transport properties of SrTiO3-based heterostructures while the crystal heterostructure is forming. Surprisingly, we detect a conducting interface already at the initial growth stage, much earlier than the well-established critical thickness limit for observing conductivity ex-situ after sample growth. We investigate how the conductivity depends on various physical processes occurring during pulsed laser depositions, including light illumination, particle bombardment by the plasma plume, interactions with the atmosphere and oxygen migration from SrTiO3 to the thin films of varying compositions. Using this approach, we propose a new design tool to control the electrical properties of interfaces in real time during their formation.

cond-mat.mtrl-sci↗

arXiv2019

Diluted Oxide Interfaces with Tunable Ground States

The metallic interface between two oxide insulators, such as LaAlO3/SrTiO3 (LAO/STO), provides new opportunities for electronics and spintronics. However, due to the presence of multiple orbital populations, tailoring the interfacial properties such as the ground state and metal-insulator transitions remains challenging. Here, we report an unforeseen tunability of the phase diagram of LAO/STO by alloying LAO with a ferromagnetic LaMnO3 insulator without forming lattice disorder and at the same time without changing the polarity of the system. By increasing the Mn-doping level, x, of LaAl1-xMnxO3/STO, the interface undergoes a Lifshitz transition at x = 0.225 across a critical carrier density of nc= 2.8E13 cm-2, where a peak TSC =255 mK of superconducting transition temperature is observed. Moreover, the LaAl1-xMnxO3 turns ferromagnetic at x >=0.25. Remarkably, at x = 0.3, where the metallic interface is populated by only dxy electrons and just before it becomes insulating, we achieve reproducibly a same device with both signatures of superconductivity and clear anomalous Hall effect. This provides a unique and effective way to tailor oxide interfaces for designing on-demand electronic and spintronic devices.

cond-mat.mtrl-sci↗