Wall Dynamics Research Articles

Disorder effects in the Z3 Fock parafermion chain

We study the effects of disorder in a one-dimensional model of $\mathbb{Z}_{3}$ Fock parafermions which can be viewed as a generalization of the prototypical Kitaev chain. Exact diagonalization is employed to determine level statistics, participation ratios, and the dynamics of domain walls. This allows us to identify ergodic as well as finite-size localized phases. In order to distinguish Anderson from many-body localization, we calculate the time evolution of the entanglement entropy in random initial states using tensor networks. We demonstrate that a purely quadratic parafermion model does not feature Anderson but many-body localization due to the nontrivial statistics of the particles.

Structures and velocities of noisy ferroelectric domain walls

Ferroelectric domain wall motion is fundamental to the switching properties of ferroelectric devices and is influenced by a wide range of factors including spatial disorder within the material and thermal noise. We build a Landau-Ginzburg-Devonshire (LGD) model of ${180}^{\ensuremath{\circ}}$ ferroelectric domain wall motion that explicitly takes into account the presence of both spatial disorder and thermal noise. We demonstrate both creep flow and linear flow regimes of the domain wall dynamics by solving the LGD equations in a Galilean frame moving with the wall velocity $v$. Thermal noise plays a key role in the wall depinning process at small fields $E$. We study the scaling of the velocity $v$ with the applied DC electric field $E$ and show that noise and spatial disorder strongly affect domain wall velocities. We also show that domain walls develop a local, metastable paraelectric region and widen significantly in the presence of thermal noise in materials with ``multiwell'' potentials, representative of ferroelectrics at temperatures $T$ just below a first-order phase transition (Curie) temperature ${T}_{c}$. These calculations point to the potential of noise and disorder to become control factors for the switching properties of ferroelectric materials, for example for advancement of microelectronic applications.

Wideband magnetic losses and their interpretation in HGO steel sheets

The magnetic properties of high-permeability grain-oriented (HGO) Fe-Si sheets have been investigated in the frequency range 1 Hz-10 kHz, with attention devoted to the role of thickness on the behavior of the magnetic losses and the phenomenology of skin effect. The study is focused on the wideband response of 0.174 mm and 0.289 mm thick sheets, comparatively tested at peak polarization values ranging between 0.25 T and 1.7 T. The experiments associate fluxmetric measurements with direct Kerr observations of the dynamics of the domain walls. A picture of the magnetization process comes to light, where the dynamics of the flux reversal takes hold under increasing frequencies through the motion of increasingly bowed 180° walls, eventually merging at the sheet surface for a fraction of the semi-period. This effect can be consistently predicted, starting from the Kerr-based knowledge of the equilibrium wall spacing, by the numerical modeling of the motion of an extended array of 180° domain walls, subjected to the balanced action of the applied and eddy current fields, and the elastic reaction of the bowed walls. This model can be incorporated into the general concept of loss separation, by calculating the classical loss component through the solution of the Maxwell’s diffusion equation under a magnetic constitutive law identified with the normal DC curve. The numerical domain wall model and the loss decomposition consistently predict that the excess loss component, playing a major role in these grain-oriented materials at power frequencies, tends to disappear in the upper induction-frequency corner.

Revealing Nanoscale Disorder in W / Co - Fe - B / MgO Ultrathin Films Using Domain-Wall Motion

Disorder in ultra-thin magnetic films can significantly hinder domain wall motion. One of the main issues on the path towards efficient domain wall based devices remains the characterization of the pinning landscape at the nanoscale. In this paper, we study domain wall motion in W/CoFeB/MgO thin films with perpendicular magnetic anisotropy crystallized by annealing at 400$^{\circ}$C and a process based on He$^{+}$ irradiation combined with elevated temperatures. Magnetic properties are similar for the whole series of samples, while the magnetic domain wall mobility is critically improved in the irradiated samples. By using an analytical model to extract nanoscale pinning parameters, we reveal important variations in the disorder of the crystallized samples. This work offers a unique opportunity to selectively analyze the effects of disorder on the domain wall dynamics, without the contribution of changes in the magnetic properties. Our results highlight the importance of evaluating the nanoscale pinning parameters of the material when designing devices based on domain wall motion, which in return can be a powerful tool to probe the disorder in ultra-thin magnetic films.

Domain wall damped harmonic oscillations induced by curvature gradients in elliptical magnetic nanowires

Understanding the domain wall (DW) dynamics in magnetic nanowires (NW) is crucial for spintronic-based applications demanding the use of DWs as information carriers. This work focuses on the dynamics of a DW displacing along a bent NW with an elliptical shape under the action of spin-polarized electric currents and external magnetic fields. Our results evidence that a curvature gradient induces an exchange-driven effective tangential field responsible for pinning a DW near the maximum curvature point in a NW. The DW equilibrium position depends on the competition between the torques produced by the external stimuli and the curvature-induced effective fields. When the external stimuli are below a certain threshold, the DW follows a damped harmonic oscillation around the equilibrium position. Above this threshold, DW displaces along the NW under an oscillatory translational motion.

Dynamics of entangled domain walls in the PXP model under driving: Crossover from prethermalization to localization

Based on the PXP model adapted for Rydberg-blockaded chains, we investigate the dynamics of topological domain walls between different quantum many-body scar states of ${\mathbb{Z}}_{2}$ symmetry. It is found that the domain walls not only possess oscillating features of scars but also manifest longstanding bipartite entanglement with exactly unchanged flip-flop phase difference, suggesting their potential as a quantum information resource. A periodically driven field is exerted and the high-frequency drive gives rise to a crossover from prethermalization to Floquet localization. In order to investigate the stability of domain walls acting as information carriers, we further simulate the collision between them and find negligible influence on each other. Subsequently, the quench dynamics with domain walls reveals exotic physics and applicable potentials of nonthermalized scar states.

Influence of climate-dependent variables on deformation and differential erosion of stratified sedimentary rocks

Rockfalls are major natural hazards for road users and infrastructures in northern Gaspésie (Eastern Canada) where nearly 25 km of road runs along imposing rockwalls. Since 1987, the Ministère des Transports du Québec (MTQ) has reported >17,500 rockfalls that have reached the roadway. While rockfalls are primarily gravitational phenomena, other factors contribute to their development. The long-term interaction of a series of processes leads to rock instabilities. They are never caused solely by the most recent visible change. This study aims to better understand the influence of climate-dependent variables on the mechanical deformations that leads to the erosion of stratified sedimentary rock sequences. To achieve this, a flysch rockwall was instrumented with crack meters and a network of hydrometeorological sensors. The major deformations affecting stratum of siltstone and sandstone were identified and correlated with climate-dependent variables. Results highlighted that irreversible deformations in the first decimeters of rock wall surface are mainly induced by rainfall and snowmelt, by temperature fluctuations around the freezing point and to a lesser extent, by large thermal variations. The water content fluctuations at the rock surface are more effective at generating irreversible deformations in the clayey siltstone strata than freeze-thaw cycles and high amplitude thermal variations. In the sandstone strata, irreversible deformations were primarily caused by freeze-thaw cycles and water content fluctuations at the rock surface. The long-term trends in the sandstone and siltstone strata recorded by crack meters, along with field observations, highlight mechanisms that lead to the development of superficial rock instabilities in this type of geology. Our results show that the retreat and settlement of the weak rock strata (clayey siltstone) causes the gradual overhang of the resistant rock strata (sandstone). As a result, sandstone blocks will eventually slide or topple on the eroding weak rock strata below. The results of this study underscore the importance of studying rock wall dynamics as a whole to understand the mechanisms that lead to the development of hazardous large-scale rock instabilities.

An alternative understanding of the skyrmion Hall effect based on one-dimensional domain wall motion

A moving magnetic skyrmion exhibits transverse deflection. This so-called skyrmion Hall effect has been explained by the Thiele equation. Here, we provide an alternative interpretation of the skyrmion Hall effect based on the dynamics of domain walls enclosing the skyrmion. We relate the spin-torque-induced local rotation of the domain wall segments to the shift of the skyrmion core, explaining the skyrmion Hall effect at the micromagnetic level. Based on our intuitive interpretation, we also show that the skyrmion Hall effect can be suppressed by combining the spin-transfer and spin–orbit torques, thereby removing the major obstacle to utilizing skyrmions in devices.

Competition between Ferroelectric and Ferroelastic Domain Wall Dynamics during Local Switching in Rhombohedral PMN-PT Single Crystals.

The possibility to control the charge, type, and density of domain walls allows properties of ferroelectric materials to be selectively enhanced or reduced. In ferroelectric-ferroelastic materials, two types of domain walls are possible: pure ferroelectric and ferroelastic-ferroelectric. In this paper, we demonstrated a strategy to control the selective ferroelectric or ferroelastic domain wall formation in the (111) single-domain rhombohedral PMN-PT single crystals at the nanoscale by varying the relative humidity level in a scanning probe microscopy chamber. The solution of the corresponding coupled electro-mechanical boundary problem allows explaining observed competition between ferroelastic and ferroelectric domain growth. The reduction in the ferroelastic domain density during local switching at elevated humidity has been attributed to changes in the electric field spatial distribution and screening effectiveness. The established mechanism is important because it reveals a kinetic nature of the final domain patterns in multiaxial materials and thus provides a general pathway to create desirable domain structure in ferroelectric materials for applications in piezoelectric and optical devices.

Effect of convective schemes in wall-resolved and wall-modeled LES of compressible wall turbulence

The current study discusses how numerical schemes and discretization approaches affect wall-resolved and wall-modeled LES outcomes. A turbulent boundary layer setup over a flat plate in both super- and hypersonic conditions is used to illustrate the effect of different numerical discretization strategies. In particular, six convective methods are examined, as well as various degrees of hybridization between shock-capturing and centered approaches: The former introducing non-negligible numerical viscosity, the latter being virtually dissipation-free. The analysis reveals that injected numerical viscosity due to upwinding procedures considerably alters wall dynamics for both wall-resolved and especially wall-modeled arrangements. In particular, if low-order or pure shock-capturing schemes are used, wall modeling fails in heading the system dynamics due to a strong modulation of main turbulent features. Conversely, realistic turbulence patterns are recovered if hybrid and/or high-order shock-capturing methods are employed. Thus, the paper establishes criteria for selecting a suitable numerical setup in wall-modeled LES, providing suggestions for grid resolution levels and convective scheme selection/hybridization. An overview perspective concerning numerical diffusion coupling with turbulent stresses in wall-resolved and wall-modeled LES is also provided.

Bubble dynamics in fluids with N -body simulations

We present a new approach to studies of bubble dynamics in fluids. Relying on particle-based simulations, this method is general and suitable for cases where the commonly used perfect fluid description fails. We study expanding true vacuum bubbles surrounded by free or self-interacting particles and quantify how self-interactions affect the terminal bubble wall velocity. We find that, for sufficiently strongly self-interacting fluids, local thermal equilibrium is maintained around the bubble wall and the fluid profile is similar to that obtained with the perfect fluid description.

Dynamics of chiral domain walls under applied current in cylindrical magnetic nanowires

The dynamics of two types of chiral magnetic domain walls in magnetic cylindrical nanowires under spin-polarized current are investigated by means of micromagnetic simulations. We show that Bloch point domain walls with chirality identical to that of the Oersted field can propagate without dynamical instabilities with velocities ∼300 m/s. The domain wall width is shown to widen at larger current densities limiting the velocity increase. For domain walls with opposite chirality, we observed a new pinning mechanism created by the action of the Oersted field, limiting their propagation distance even after chirality switching. Vortex–antivortex domain walls transform into Bloch point domain walls, and after that they can unexpectedly propagate either along or against the direction of the current. Our findings demonstrate that domain wall dynamics under current in cylindrical magnetic nanowires can result in a plethora of different behaviors that will have important implications for future 3D spintronic devices.

Thermal stability of nanoscale ferroelectric domains by molecular dynamics modeling

Ultra-dense domain walls are increasingly important for many devices but their microscopic properties are so far not fully understood. In this study we combine atomistic and coarse-grained molecular dynamic simulations to study the domain wall stability in the prototypical ferroelectric BaTiO3. We transfer the discussion of the field-driven nucleation and motion of domain walls to thermally induced modifications of the wall without an external driving force. Our simulations show that domain wall dynamics and stability depend crucially on microscopic thermal fluctuations. Enhanced fluctuations at domain walls may result in the formation of critical nuclei for the permanent shift of the domain wall. If two domain walls are close - put in other words, when domains are small - thermal fluctuations can be sufficient to bring domain walls into contact and lead to the annihilation of small domains. This is even true well below the Curie temperature and when domain walls are initially as far apart as 6 unit cells. Such small domains are, thus, not stable and limit the maximum achievable domain wall density in nanoelectronic devices.

P-150 TRANSVERSUS ABDOMINIS RELEASE BY MINIMAL INVASIVE SURGERY. OUR EXPERIENCE IN A TERCIARY HOSPITAL

Abstract Aim We present the experience in the transversus abdominis release (TAR) technique using a minimally invasive approach in our center. Methods We expose those W3 defects intervened by laparoscopic TAR(n=6). Step 1: Releasing adhesions from previous surgeries. Step 2: Bilateral Rives space dissection, as well as the Rossen's space, this one using “down to up” technique. Step 3: Closure of the gap with barbed suture. In all cases, a PVDF mesh has been associated with atraumatic fixation, and 2 drains were placed. Results The mean age was 62, 100% men, and their BMI was greater than 25Kg/m2. All underwent scheduled surgery, using a minimally invasive approach, placing the mesh at the retromuscular level. Postoperative stay was 7.6 days. We did not obtain major complications (perforation, bleeding), but a drainage hole wound infection was registered. We had no readmissions or any medical complications. Follow-up of 12 months, without signs of recurrence or chronic pain. Conclusions Although Robotic surgery and Botulinum toxin in surgery seems to be the future, in our experience TAR technique performed by laparoscopy is useful for large midline incisional hernias treatment as well as those associated with a lateral component in a terciary Hospital. We obtain good results in terms of recurrence and restoration of the abdominal wall dynamics. However, further studies are necessary to be carried out by experienced teams to reach conclusions.

Dynamic Bloch Chirality and Enhanced Velocities from Spin-Orbit Torque Driven Domain Wall Motion in Thick Magnetic Films

Spin-orbit torque (SOT) driven domain wall motion has attracted significant attention as the basis for a variety of spintronic devices due to its potential use as a high speed, low power means to manipulate the magnetic state of an object. While most previous attention has focused on ultrathin films wherein the material thickness is significantly less than the magnetic exchange length, recent reports have suggested unique dynamics may be achieved in intermediate and high thickness films. We used micromagnetic modelling to explore the role of the vertically non-uniform spin textures associated with the domain wall in nanowires of varying thickness on SOT driven domain wall motion. We found large velocity asymmetries between Bloch chiralities near the current density required for reversal of the Bloch component of the magnetization and linked these asymmetries to a gradual reorientation of the domain wall structure which drives a non-negligible, chiral Néel component of the domain wall. We further explored the influence of saturation magnetization, film thickness, the Dzyaloshinskii-Moriya interaction, and in-plane fields on domain wall dynamics. These results provide a framework for the development of SOT based devices based on domain wall motion in nanowires beyond the ultrathin film limit.

Analysis of 'enhanced-view totally extra-peritoneal' (eTEP) approach for ventral hernia: Early results.

Laparoscopic ventral hernia repair is undergoing a paradigm shift with the introduction of numerous new techniques to improve the outcomes. Enhanced-view totally extra-peritoneal (eTEP) is a novel approach for the repair of ventral herniae introduced by Belyansky et al. The key innovation lies in placing the mesh in a large retrorectus-pre-peritoneal space contrary to the widely practiced intra-peritoneal placement. This approach can be easily coupled with a component separation in the form of transversus abdominis release (TAR) for large herniae. We conducted a midterm analysis of 'eTEP' approach to ventral hernia at a high-volume tertiary care centre and present our results of over 3 years of employing this technique. A retrospective study of 150 cases of ventral hernia repaired using eTEP approach from January 2018 to February 2021 at a tertiary care centre by a team of three surgeons. The procedures were performed by a single team of three members headed by the first author. Out of total 150 cases, incisional hernia occurred in 73 cases (48.7%), primary hernia occurred in 48 cases (32%) and recurrent hernia in 29 cases (19.3%). Although the majority of incisional (87.7%) and recurrent (79.3%) ventral hernias occurred in female, the incidence of primary ventral hernia was equal at 24 cases in both genders. The majority of the cases (80.7%) underwent eTEP RS procedure, and the rest were W3 hernias, which were managed by including a component separation in the form of eTEP TAR. The operating time for eTEP TAR (222.24 min ± 32.56) compared to eTEP RS (124.33 ± 23.68) was significantly longer. The mean length of stay was significantly shorter for primary hernias (3.75 days ± 1.62) compared to recurrent (5.21 days ± 2.51) and incisional hernias (4.36 days ± 2.19) (F = 4.376) (P = 0.014). The peri-operative period was uneventful in majority of the cases. We experienced a seroma rate of 5.8% in our series. At follow-up of 1 year, 3.3% of patients complained of discomfort/bulge in the upper abdomen. There were no other surgical site occurrences (SSO) in the form infection, posterior rectus sheath disruption and skin necrosis. We observed no recurrences till date with a minimum follow-up of 1 year. eTEP approach to ventral hernia is a promising abdominal wall reconstruction technique. It is safe and offers good functional outcomes with restoration of abdominal wall dynamics. It is a reproducible and safe technique for tackling various types of ventral hernia. It is specifically useful in managing unusual lateral hernias, incisional and recurrent hernias with ease.

ABDOMINAL COMPRESSION IN END-STAGE FIBROTIC INTERSTITIAL LUNG DISEASE (ILD) IMPROVES RESPIRATORY COMPLIANCE

ABDOMINAL COMPRESSION IN END-STAGE FIBROTIC INTERSTITIAL LUNG DISEASE (ILD) IMPROVES RESPIRATORY COMPLIANCE

Study of Domain Wall Dynamics in GdFeCo Using Double High-Speed Photography

Study of Domain Wall Dynamics in GdFeCo Using Double High-Speed Photography

Tuning the Dynamics of Chiral Domain Walls of Ferrimagnetic Films by Magnetoionic Effects

The manipulation of magnetism with a gate voltage is expected to lead the way towards the realization of energy-efficient spintronics devices and high-performance magnetic memories. Exploiting magneto-ionic effects under micro-patterned electrodes in solid-state devices adds the possibility to modify magnetic properties locally, in a non-volatile and reversible way. Tuning magnetic anisotropy, magnetization and Dzyaloshinskii-Moriya interaction allows modifying at will the dynamics of non trivial magnetic textures such as skyrmions and chiral domain walls in magnetic race tracks. In this work, we illustrate efficient magneto-ionic effects in a ferrimagnetic Pt/Co/Tb stack using a ZrO2 thin layer as a solid state ionic conductor. When a thin layer of terbium is deposited on top of cobalt, it acquires a magnetic moment that aligns antiparallel to that of cobalt, reducing the effective magnetization. Below the micro-patterned electrodes, the voltage-driven migration of oxygen ions in a ZrO2 towards the ferrimagnetic stack partially oxidizes the Tb layer, leading to the local variation not only of the spontaneous magnetization, but also of the effective magnetic anisotropy and of the Dzyaloshinskii-Moriya interaction. This leads to a huge increase of the domain wall velocity, which varies from 10 m/s in the pristine state to 250 m/s after gating. This non-volatile and reversible tuning of the domain wall dynamics may lead to applications to reprogrammable magnetic memories or other spintronic devices.

Discrete Time-Crystalline Response Stabilized by Domain-Wall Confinement

Discrete time crystals represent a paradigmatic nonequilibrium phase of periodically driven matter. Protecting its emergent spatiotemporal order necessitates a mechanism that hinders the spreading of defects, such as localization of domain walls in disordered quantum spin chains. In this work, we establish the effectiveness of a different mechanism arising in clean spin chains: the confinement of domain walls into ``mesonic'' bound states. We consider translationally invariant quantum Ising chains periodically kicked at arbitrary frequency, and discuss two possible routes to domain-wall confinement: longitudinal fields and interactions beyond nearest neighbors. We study the impact of confinement on the order parameter evolution by constructing domain-wall-conserving effective Hamiltonians and analyzing the resulting dynamics of domain walls. On the one hand, we show that for arbitrary driving frequency the symmetry-breaking-induced confining potential gets effectively averaged out by the drive, leading to deconfined dynamics. On the other hand, we rigorously prove that increasing the range $R$ of spin-spin interactions $J_{i,j}$ beyond nearest neighbors enhances the order-parameter lifetime \textit{exponentially} in $R$. Our theory predictions are corroborated by a combination of exact and matrix-product-state simulations for finite and infinite chains, respectively. The long-lived stability of spatiotemporal order identified in this work does not rely on Floquet prethermalization nor on eigenstate order, but rather on the nonperturbative origin of vacuum-decay processes. We point out the experimental relevance of this new mechanism for stabilizing a long-lived time-crystalline response in Rydberg-dressed spin chains.