arXiv subjects

Louis Alaerts

Publications and source records attributed to Louis Alaerts.

6 recordsLinked to original sources

arXiv2026

Discovery of a new weberite-type antiferroelectric: La3NbO7

Antiferroelectrics are antipolar materials which possess an electric field-induced phase transition to a polar, ferroelectric phase and offer significant potential for sensing/actuation and energy-storage applications. Known antiferroelectrics are relatively scarce and mainly based on a limited set of perovskite materials and their alloys (e.g., PbZrO$_3$, AgNbO$_3$, NaNbO$_3$). Here, a new family of lead-free, weberite-type antiferroelectrics, identified through a large-scale, first-principles computational search is introduced. The screening methodology, which connects lattice dynamics to antipolar distortions, predicted that La$_3$NbO$_7$ could exhibit antiferroelectricity. We confirm the prediction through the synthesis and characterization of epitaxial La$_3$NbO$_7$ thin films, which display the signature double hysteresis loops of an antiferroelectric material as well as clear evidence of an antipolar ground state structure from transmission electron microscopy. The antiferroelectricity in La$_3$NbO$_7$ is simpler than most known antiferroelectrics and can be explained by a Kittel-type mechanism involving the movement of niobium atoms in an oxygen octahedron through a single phonon mode which results in a smaller change in the volume during the field-induced phase transition. Additionally, it is found that La$_3$NbO$_7$ combines a high threshold field with a high breakdown field ($\approx$ 6MV/cm) - which opens up opportunities for energy-storage applications. This new weberite-type family of materials offers many opportunities to tune electrical and temperature response especially through substitutions on the rare-earth site. Ultimately, this work demonstrates a successful data-driven theory-to-experiment discovery of an entirely new family of antiferroelectrics and provides a blueprint for the future design of ferroic materials.

cond-mat.mtrl-sci↗

arXiv2025

Direct determination of antiferroelectric-to-ferroelectric phase transition pathways in PbZrO$_3$ with Operando Electron Microscopy

Under a sufficiently high applied electric field, a non-polar antiferroelectric material, such as \ce{PbZrO3}, can undergo a rapid transformation to a polar ferroelectric phase. While this behavior is promising for energy storage and electromechanical applications, a complete understanding of the atomic-scale mechanisms governing the phase transition remain elusive. Here, we employ \textit{operando} scanning transmission electron microscopy electric field biasing to directly resolve the antiferroelectric-to-ferroelectric transition pathway in \ce{PbZrO3} thin films under device-relevant conditions. Atomic-resolution imaging reveals a multi-step transition that includes several metastable phases. Complementary nano-beam electron diffraction and atomic scale analysis further show that this pathway and its end states can be modulated, leading to the formation of a \quotes{dead layer} near the substrate with suppressed switching behavior. Taking advantage of this depth-dependent heterogeneity, dynamic phase transformations are observed between coexisting antiferroelectric and metastable ferroelectric phases. At this dynamic transition front, repeated phase interconversion is shown to be driven by competing internal (due to substrate clamping and extended defects) and external fields, allowing the relative energies of intermediate phases to be compared as a function of electric field. This work highlights the critical role of local energetics in phase stability and provides key experimental insights into field-induced phase transitions, guiding the design of antiferroelectric-based devices.

cond-mat.mtrl-sci↗

arXiv2025

First principles computations of the Stark shift of a defect-bound exciton: the case of the T center in silicon

The T center in silicon has recently drawn a lot of attention for its potential in quantum information science. The sensitivity of the zero-phonon line (ZPL) to electrical field was recently investigated by a combination of different experimental methods but there is still no first principles study on the Stark shift of the T center. Dealing with the defect-bound exciton nature of the excited state is particularly challenging using density functional theory because of the large spatial delocalization associated with the wavefunction. Here, we tackle this issue by performing a convergence study over the supercell size. We obtain an exciton binding energy of 28.5meV, in good agreement with experimental results. We then calculate the Stark shift through the dipole moment change of the ZPL transition of the T center using the modern theory of polarization formalism and find a modest linear coefficient of $\Delta \mu$=0.79D along X and $\Delta \mu$=0.03D along Y. We discuss our results in light of the recent experimental measurements of the Stark shift. Our analysis suggests that bound-exciton defects could be particularly sensitive to local field effect as a result of their large spatial extent.

cond-mat.mtrl-sci↗

arXiv2024

Optical transition parameters of the silicon T centre

The silicon T centre's narrow, telecommunications-band optical emission, long spin coherence, and direct photonic integration have spurred interest in this emitter as a spin-photon interface for distributed quantum computing and networking. However, key parameters of the T centre's spin-selective optical transitions remain undetermined or ambiguous in literature. In this paper we present a Hamiltonian of the T centre TX state and determine key parameters of the optical transition from T$_0$ to TX$_0$ from a combined analysis of published results, density functional theory, and new spectroscopy. We resolve ambiguous values of the internal defect potential in the literature, and we present the first measurements of electrically tuned T centre emission. As a result, we provide a model of the T centre's optical and spin properties under strain, electric, and magnetic fields that can be utilized for realizing quantum technologies.

quant-ph↗

arXiv2024

A first principles study of the Stark shift effect on the zero-phonon line of the NV center in diamond

Point defects in semiconductors are attractive candidates for quantum information science applications owing to their ability to act as spin-photon interface or single-photon emitters. However, the coupling between the change of dipole moment upon electronic excitation and stray electric fields in the vicinity of the defect, an effect known as Stark shift, can cause significant spectral diffusion in the emitted photons. In this work, using first principles computations, we revisit the methodology to compute the Stark shift of point defects up to the second order. The approach consists of applying an electric field on a defect in a slab and monitoring the changes in the computed zero-phonon line (i.e., difference in energy between the ground and excited state) obtained from constraining the orbital occupations (constrained-DFT). We study the Stark shift of the negatively charged nitrogen-vacancy (NV) center in diamond using this slab approach. We discuss and compare two approaches to ensure a negatively charged defect in a slab and we show that converged values of the Stark shift measured by the change in dipole moment between the ground and excited states ($\Delta \mu$) can be obtained. We obtain a Stark shift of $\Delta \mu$=2.68D using the semi-local GGA-PBE functional and of $\Delta \mu$=2.23D using the HSE hybrid-functional. These values are in good agreement with experimental results. We also show that modern of theory of polarization can be used on constrained-DFT to obtain Stark shifts in very good agreement with the slab computations.

cond-mat.mtrl-sci↗

arXiv2020

Ferroelectricity and multiferroicity in anti-Ruddlesden-Popper structures

Combining ferroelectricity with other properties such as visible light absorption or long-range magnetic order requires the discovery of new families of ferroelectric materials. Here, through the analysis of a high-throughput database of phonon band structures, we identify a new structural family of anti-Ruddlesden-Popper phases A$_4$X$_2$O (A=Ca, Sr, Ba, Eu, X=Sb, P, As, Bi) showing ferroelectric and anti-ferroelectric behaviors. The discovered ferroelectrics belong to the new class of hyperferroelectrics which polarize even under open-circuit boundary conditions. The polar distortion involves the movement of O anions against apical A cations and is driven by geometric effects resulting from internal chemical strains. Within this new structural family, we show that Eu$_4$Sb$_2$O combines coupled ferromagnetic and ferroelectric order at the same atomic site, a very rare occurrence in materials physics.

cond-mat.mtrl-sci↗