Domain Walls In Phase Research Articles

Strain phase equilibria and phase‐field method of ferroelectric polydomain: A case study of monoclinic KxNa1 − xNbO3 thin films

AbstractKnowledge of the thermodynamic equilibria and domain structures of ferroelectrics is critical to establishing their structure–property relationships that underpin their applications from piezoelectric devices to nonlinear optics. Here, we establish the strain condition for strain phase separation and polydomain formation and analytically predict the corresponding domain volume fractions and wall orientations of, relatively low symmetry and theoretically more challenging, monoclinic ferroelectric thin films by integrating thermodynamics of ferroelectrics, strain phase equilibria theory, microelasticity, and phase‐field method. Using monoclinic KxNa1 − xNbO3(0.5 < x < 1.0) thin films as a model system, we establish the polydomain strain–strain phase diagrams, from which we identify two types of monoclinic polydomain structures. The analytically predicted strain conditions of formation, domain volume fractions, and domain wall orientations for the two polydomain structures are consistent with phase‐field simulations and in good agreement with experimental results in the literature. The present study demonstrates a general, powerful analytical theoretical framework to predict the strain phase equilibria and domain wall orientations of polydomain structures applicable to both high‐ and low‐symmetry ferroelectrics and provide fundamental insights into the equilibrium domain structures of ferroelectric KxNa1 − xNbO3 thin films that are of technology relevance for lead‐free dielectric and piezoelectric applications.

Frequency-selective valley-edge transmission and channeling in phononic-crystal plates with dual topological modulations

In this numerical study, we propose dual-modulated topological pillared phononic crystal (PnC) plates and demonstrate their application in achieving frequency-selective waveguiding of Lamb-wave valley-edge states. We show that both the radius and the height of the pillars in the honeycomb unit cell can be varied, allowing a generalized parameter space to obtain the complete topological bandgaps and two groups of distinct valley Hall phases for designing topological waveguides operating in different frequency ranges. Accordingly, we construct different types of phase domain walls to support valley-edge states using the dual-modulated PnC plates with a lattice constant of 2000 μm and with topological bandgaps opened around the Dirac cone frequency of 426 kHz. The numerical results show that the valley-edge states emerge to cover different frequency ranges and exhibit robust backscattering immunity when propagating along zigzag paths with sharp corners. Furthermore, the transport path of the valley-edge states can be designed to be highly dependent on the operating frequency in different domain walls. Consequently, we design a straight waveguide and three multichannel waveguides to demonstrate frequency-dependent switchable transmission and selective channeling of valley-edge states, respectively. The results of this study pave the way for the development and optimization of topological acoustic circuits using the generalized parameter space approaches and are expected to find promising applications in frequency-controlled and signal-division devices.

Giant piezoelectricity of PNN-PIN-PT ceramics via domain engineering

The ferroelectric domain plays an important role in determining the piezoelectric performance of ferroelectric ceramics. Herein, LiNbO3 (LN) is used as an additive to tune the ferroelectric domain of 0.49Pb(Ni1/3Nb2/3)O3-0.2Pb(In1/2Nb1/2)O3-0.31PbTiO3 (PNN-PIN-PT) ceramics. PNN-PIN-PT-0LN ceramic exhibits the ordered tetragonal phase (90 °) domain wall and rhombohedral phase (71 ° and 109 °) domain wall. Incorporating LN into the system leads to the transformation of the majority of structured macro-domains into random micro-domains with smaller sizes, which disrupt their long-range ordered ferroelectric domains, resulting in significant piezoelectric enhancement. Compared to PNN-PIN-PT-0LN ceramics, PNN-PIN-PT-1.8LN ceramics exhibit giant piezoelectric responses with d33 = 1112 pC/N, d31 =521 pC/N, d33*=1220 pm/V (@ E = 5 kV/cm), εr = 12092. These findings shed light on a specific aspect of domain engineering in piezoelectric materials, thus contributing to a more comprehensive understanding of the underlying factors that give rise to the phenomenon of giant piezoelectricity.

Multiple-q current states in a multicomponent superconducting channel

It is well-established that multicomponent superconductors can host different nonstandard phenomena such as broken-time reversal symmetry (BTRS) states, exotic Fulde–Ferrell–Larkin–Ovchinnikov phases, the fractional Josephson effect as well as plenty of topological defects like phase solitons, domain walls and unusual vortex structures. We show that in the case of a two-component superconducting quasi-one-dimensional channel this catalogue can be extended by a novel inhomogeneous current state, which we have termed as a multiple-q state, characterized by the coexistence of two different interpenetrating Cooper pair condensates with different total momenta. Within the Ginzburg–Landau formalism for a dirty two-band superconductor with sizable impurity scattering treated in the Born-approximation we reveal that under certain conditions, the occurrence of multiple-q states can induce a cascade of transitions involving switching between them and the homogeneous BTRS (non-BTRS) states and vice versa leading this way to a complex interplay of homogeneous and inhomogeneous current states. We find that hallmarks of such a multiple-q state within a thin wire or channel can be a saw-like dependence of the depairing current and the existence of two distinct stable branches on it (a bistable current state).

The NANOGrav 15 yr Data Set: Search for Signals from New Physics

The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence for the presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations of this signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, cosmic strings, and domain walls. We find that, with the exception of stable cosmic strings of field theory origin, all these models can reproduce the observed signal. When compared to the standard interpretation in terms of inspiraling supermassive black hole binaries (SMBHBs), many cosmological models seem to provide a better fit resulting in Bayes factors in the range from 10 to 100. However, these results strongly depend on modeling assumptions about the cosmic SMBHB population and, at this stage, should not be regarded as evidence for new physics. Furthermore, we identify excluded parameter regions where the predicted GW signal from cosmological sources significantly exceeds the NANOGrav signal. These parameter constraints are independent of the origin of the NANOGrav signal and illustrate how pulsar timing data provide a new way to constrain the parameter space of these models. Finally, we search for deterministic signals produced by models of ultralight dark matter (ULDM) and dark matter substructures in the Milky Way. We find no evidence for either of these signals and thus report updated constraints on these models. In the case of ULDM, these constraints outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons.

Electronic states of domain walls in commensurate charge density wave ground state and mosaic phase in 1T -TaS2

Domain walls (DWs) in the charge-density-wave (CDW) Mott insulator 1T-TaS2 have unique localized states, which play an important role in exploring the electronic properties of the material. However, the electronic states in DWs in 1T-TaS2 have not been clearly understood, mostly due to the complex structures, phases, and interlayer stacking orders in the DW areas. Here, we explored the electronic states of DWs in the large-area CDW phase and mosaic phase of 1T-TaS2 by scanning tunneling spectroscopy. Due to the different densities of DWs, the electronic states of DWs show distinct features in these phases. In the large area CDW phase, both the domain and the DWs (DW1, DW2, DW4) have zero conductance at the Fermi level; while in the mosaic phase, they can be metallic or insulating depending on their environments. In areas with a high density of DWs, some electronic states were observed both on the DWs and within the domains, indicating delocalized states over the whole region. Our work contributes to further understanding of the interplay between CDW and electron correlations in 1T-TaS2.

Phase transformations in an Aurivillius layer structured ferroelectric designed using the high entropy concept

A single phase four-layer Aurivillius structured ferroelectric ceramic, (Ca0.2Sr0.2Ba0.2Pb0.2Nd0.1Na0.1)Bi4Ti4O15 (6ABTO) was obtained using a high entropy design concept. The material, which has orthorhombic symmetry in space group A21am at room temperature, has Ca2+, Sr2+, Ba2+, Pb2+, Nd3+ and Na+ distributed not only on the A sites of the perovskite layer but also in the bismuthate layer. 6ABTO shows complex ferroelectric behavior, with a Curie point of 557 °C. Four current peaks are observed in the current - electric field curve. These peaks are attributed to a combination of a field induced phase transition and domain wall switching, which is the first reported occurrence of such current - electric field behavior for an Aurivillius structured ferroelectric material. Despite the level of disorder between the A site cations in the perovskite layer and the Bi positions in the bismuthate layer, 6ABTO does not show the relaxor ferroelectric behavior, that is commonly observed in cases of such disorder. This suggests that relaxor behavior in ferroelectrics, may be more associated with the thermal stability of dipoles, rather than the presence of polar nano-regions formed as a result of chemical disorder. The nature of the high entropy effect in 6ABTO is discussed through comparison of results from isostructural compositions containing 5, 4 and 3 of the component cations

Gravitational waves from minisplit SUSY

We show that color-breaking vacua may develop at high temperature in the Mini-Split Supersymmetry (SUSY) scenario. This can lead to a nontrivial cosmological history of the Universe, including strong first order phase transitions and domain wall production. Given the typical PeV energy scale associated with Mini-Split SUSY models, a stochastic gravitational wave background at frequencies around 1 kHz is expected. We study the potential for detection of such a signal in future gravitational wave experiments.

Evidence for different gravitational-wave sources in the NANOGrav dataset

The NANOGrav Collaboration recently reported a strong evidence for a stochastic common-spectrum process in the pulsar-timing data. We evaluate the evidence of interpreting this process as mergers of super massive black hole binaries and/or various stochastic gravitational wave background sources in the early Universe, including first-order phase transitions, cosmic strings, domain walls, and large amplitude curvature perturbations. We discuss the implications of the constraints on these possible sources. It is found that the cosmic string is the most favored source against other gravitational wave sources based on the Bayes factor analysis.

Curvature-induced emergence of a second critical field for domain wall dynamics in bent nanostripes

We investigate the dynamics of a transverse domain wall (DW) in a bent nanostripe under an external field and spin-polarized current. Besides the standard Walker breakdown phenomenon, we show the emergence of a second Walker-like critical field, which depends on both the curvature of the nanostripe and its cross section geometry. At this field, DW can change its phase, i.e., can be re-oriented along another direction with respect to the nanostripe face. Additionally, we show that the amplitude and frequency of the DW oscillations above the Walker breakdown field also depend on the nanostripe geometry and can be controlled by external stimuli. Our results evidence that the inclusion of local curvatures in nanostripes is an important component for applications that demand an adequate control of the DW phase by the proper choice of external stimuli.

Phase modulated domain walls and dark solitons for surface gravity waves

We report theoretical prediction of localized solutions for dynamics of surface gravity waves, at the critical point kh≈1.363, modelled by higher-order nonlinear Schrödinger equation. The model possesses domain walls (kink solitons) and dark solitons modulated through different phase profiles. The parametric domains are delineated for the existence of soliton solutions. The effects of wave parameters have been discussed on the amplitude of surface gravity waves. Our work is motivated by Tsitoura et al. [1], on experimental and analytical observation of phase domain walls for deep water surface gravity waves modelled by nonlinear Schrödinger equation.

Theoretical investigation of twin boundaries in WO3 : Structure, properties, and implications for superconductivity

We present a theoretical study of the structure and functionality of ferroelastic domain walls in tungsten trioxide, WO$_3$. WO$_3$ has a rich structural phase diagram, with the stability and properties of the various structural phases strongly affected both by temperature and by electron doping. The existence of superconductivity is of particular interest, with the underlying mechanism as of now not well understood. In addition, reports of enhanced superconductivity at structural domain walls are particularly intriguing. Focusing specifically on the orthorhombic $\beta$ phase, we calculate the structure and properties of the domain walls both with and without electron doping. We use two theoretical approaches: Landau-Ginzburg theory, with free energies constructed from symmetry considerations and parameters extracted from our first-principles density functional calculations, and direct calculation using large-scale, GPU-enabled density functional theory. We find that the structure of the $\beta$-phase domain walls resembles that of the bulk tetragonal $\alpha_1$ phase, and that the electronic charge tends to accumulate at the walls. Motivated by this finding, we perform ab initio computations of electron-phonon coupling in the bulk $\alpha_1$ structure and extract the superconducting critical temperatures , $T_c$, within Bardeen-Cooper-Schrieffer theory. Our results provide insight into the experimentally observed unusual trend of decreasing Tc with increasing electronic charge carrier concentration.

Gravitational waves from first-order phase transition and domain wall

In many particle physics models, domain walls can form during the phase transition process after the breakdown of the discrete symmetry. Utilizing the ℤ3 symmetric complex singlet scalar extension of the Standard Model, we study the gravitational waves produced by the strongly first-order electroweak phase transition and the domain wall decay. The gravitational wave spectrum is of a typical two-peak shape. The high frequency peak corresponding to the strongly first-order electroweak phase transition is able to be probed by the future space-based interferometers, and the low frequency peak coming from the domain wall decay is far beyond the capability of the current Pulsar Timing Arrays, and future Square Kilometer Array.

Displacive phase-field crystal model

A phase-field crystal model that spontaneously undergoes displacive phase transitions is introduced by explicitly studying a two-component two-dimensional square crystal reminiscent of a perovskite. When the intercomponent free energy is a simple polynomial, the crystal undergoes displacive transitions in the $\ensuremath{\langle}10\ensuremath{\rangle}$ and $\ensuremath{\langle}11\ensuremath{\rangle}$ directions. When the interaction is a correlation function, displacements in any direction can occur. This displacive phase-field crystal (DPFC) model maps to Landau-Ginzburg-Devonshire (LGD) theories for ferroelectrics, and the DPFC and LGD models are compared in terms of phase transitions and domain walls. Dynamical simulations of quadrijunctions were also performed and found stable spiraling quadrijunctions and unstable nonspiraling quadrijunctions. Last, domain coarsening across a small-angle grain boundary demonstrates multiple forms of non-mean-curvature-driven growth.

Iodine Adsorption on Ni(110): 2D-Phase Transitions and NiI2 Growth

Scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, and density functional theory calculations have been used to investigate I2 adsorption on the Ni(110) surface. Dissociative adsorption takes place rapidly to form a c(2 × 2) layer at an iodine coverage of 0.5 ML. DFT calculations show that hollow sites are energetically preferable for iodine adsorption on the Ni(110) surface. Increase of iodine coverage above 0.5 ML leads to the commensurate–incommensurate phase transition via nucleation of loops of domain walls and to their subsequent ordering into the striped superstructure. At saturation, a striped domain-wall phase degenerates into the uniaxially compressed quasi-hexagonal phase. Further iodine dosing leads to the nucleation and growth of 2D nickel iodide islands.

Polar and phase domain walls with conducting interfacial states in a Weyl semimetal MoTe2

Much of the dramatic growth in research on topological materials has focused on topologically protected surface states. While the domain walls of topological materials such as Weyl semimetals with broken inversion or time-reversal symmetry can provide a hunting ground for exploring topological interfacial states, such investigations have received little attention to date. Here, utilizing in-situ cryogenic transmission electron microscopy combined with first-principles calculations, we discover intriguing domain-wall structures in MoTe2, both between polar variants of the low-temperature(T) Weyl phase, and between this and the high-T higher-order topological phase. We demonstrate how polar domain walls can be manipulated with electron beams and show that phase domain walls tend to form superlattice-like structures along the c axis. Scanning tunneling microscopy indicates a possible signature of a conducting hinge state at phase domain walls. Our results open avenues for investigating topological interfacial states and unveiling multifunctional aspects of domain walls in topological materials.

Decay of the relative phase domain wall into confined vortex pairs: The case of a coherently coupled bosonic mixture

A domain wall of relative phase in a flattened harmonically-trapped Bose-Einstein condensed mixture of two atomic hyperfine states, subject to a stationary Rabi coupling of intensity $\Omega$, is predicted to decay through two different mechanisms. For small values of $\Omega$ the instability has an energetic nature and is associated with the formation of a vortex-antivortex pair of the same atomic hyperfine states, whose motion inside the trap causes the emergence of magnetization, the bending of the domain wall and its consequent fragmentation. For large values of $\Omega$ the domain wall instead undergoes a dynamic snake instability, caused by the negative value of its effective mass and results in the fast fragmentation of the wall into smaller domain walls confining vortex pairs of different atomic species. Numerical predictions are given by solving the time-dependent Gross-Pitaevskii equation in experimentally available configurations of mixtures of sodium atomic gases.

Phase transition and enhanced properties in perovskite-type piezoceramics from the view of energy

In the work, rotational factors (ω, φ and δ), representative of the degree of spontaneous polarization’s rotation among different ferroelectric phases, were introduced to qualitatively describe Gibbs energy of perovskite-type piezoelectric ceramics. Phase transition and domain wall motion which are essential for enhanced piezoelectric properties were explained on energy basis. The results suggested Gibbs energy decreased with the decrease of rotation angle in different paths (O–T, R–T and R–O path) and according to Curie’s principle, lattice deformation and associated phase transition happened, which were well observed through Raman analysis. Domain wall motion was discussed taking magnetic materials as a reference and enhanced properties of perovskite-type piezoceramics were illustrated in the view of domain wall motion. Besides, contributions of ferroelectric microdomain to domain wall motion which played an important role in piezoelectric properties are also discussed here.

Active subspace analysis and uncertainty quantification for a polydomain ferroelectric phase-field model

We perform parameter subset selection and uncertainty analysis for phase-field models that are applied to the ferroelectric material lead titanate. A motivating objective is to determine which parameters are influential in the sense that their uncertainties directly affect the uncertainty in the model response, and fix noninfluential parameters at nominal values for subsequent uncertainty propagation. We employ Bayesian inference to quantify the uncertainties of gradient exchange parameters governing 180° and 90° tetragonal phase domain wall energies. The uncertainties of influential parameters determined by parameter subset selection are then propagated through the models to obtain credible intervals when estimating energy densities quantifying polarization and strain across domain walls. The results illustrate various properties of Landau and electromechanical coupling parameters and their influence on domain wall interactions. We employ energy statistics, which quantify distances between statistical observations, to compare credible intervals constructed using a complete set of parameters against an influential subset of parameters. These intervals are obtained from the uncertainty propagation of the model input parameters on the domain wall energy densities. The investigation provides critical insight into the development of parameter subset selection, uncertainty quantification, and propagation methodologies for material modeling domain wall structure evolution, informed by density functional theory simulations.

Anomalous domain wall condensation in a modified Ising chain

We construct a one-dimensional local spin Hamiltonian with an intrinsically non-local, and therefore anomalous, global $\mathbb{Z}_2$ symmetry. The model is closely related to the quantum Ising model in a transverse magnetic field, and contains a parameter that can be tuned to spontaneously break the non-local $\mathbb{Z}_2$ symmetry. The Hamiltonian is constructed to capture the unconventional properties of the domain walls in the symmetry broken phase. Using uniform matrix product states, we obtain the phase diagram that results from condensing the domain walls. We find that the complete phase diagram includes a gapless phase that is separated from the ordered ferromagnetic phase by a Berezinskii-Kosterlitz-Thouless transition, and from the ordered antiferromagnetic phase by a first order phase transition.