Step-like Behavior Research Articles

Displacement prediction for landslide with step-like behavior based on stacking ensemble learning strategy

Displacement prediction for landslide with step-like behavior based on stacking ensemble learning strategy

Double ferromagnetic barriers resonant tunneling diodes (RTD) based on the surface of a topological insulator

Resonant tunneling diodes (RTDs), which are based on double barrier quantum well structures, are typically achieved by combining different materials with varying band gap sizes. However, this approach often poses challenges such as material mismatching and dislocations. In this study, we present a novel resonant tunneling diode scheme utilizing the unique properties of topological insulator materials. Specifically, we exploit the gap opening in the band structure of the topological insulator by employing perpendicular magnetization. In this proposed RTD platform, the barrier regions are formed from a ferromagnetic topological insulator through the proximity effect. By adjusting the thickness and spacing of the ferromagnetic barriers, a well region with confined states emerges between the barrier regions. Theoretical analysis reveals that by tuning the back gate voltage, the I-V characteristics exhibit two significant behaviors: negative differential resistance (NDR) and step-like behavior for Fermi energy values of EF = −3 and EF = 3, respectively. Furthermore, we observe an increase in the peak-to-valley ratio (PVR) with higher magnetization values. Notably, the PVR reaches a value of 7.13 for a magnetization value of m = 9. Additionally, we investigate the influence of the well width and barrier thickness on the transport properties of the device.

Surface-state-related carrier dynamics of GaAs determined by UV-visible pump-probe terahertz spectroscopy

The surface velocity and the bulk lifetime of photo-excited free carriers in GaAs were measured using an optical-pump and THz-probe time-domain technique. By varying the pump laser photon energy from 1.56 to 4.15 eV, we observe that the surface velocity drops abruptly from 0.7×106 cm/s down to 0.2×106 cm/s at 2.5 eV, while the bulk lifetime remains almost constant. We tentatively explain this step-like behavior of the surface velocity vs the photon energy by a trapping of the free carriers at surface states, whose density of states shows a maximum at 2.5 eV.

The thermo-optical coefficient as an alternative probe for the structural arrest of polymeric glass formers

The most important, yet independent susceptibilities to characterize the canonical glass transition include the thermal expansion, the specific heat and the shear modulus. At the glass transition, all these susceptibilities show a step-like behaviour as a function of temperature. However, in principle, different susceptibilities provide different perspectives on the glass transition. Due to the effect of sample history and considerable kinetic influences on the thermal glass transition behaviour, the best way to evaluate these different perspectives is to investigate them simultaneously. In this publication, different perspectives on the dynamical freezing process are obtained by a single experimental method: Temperature-modulated optical refractometry (TMOR). TMOR is used to simultaneously investigate the dynamic thermal expansion and, indirectly, the shear viscosity of a model polymer, both contributing to the thermo-optical coefficient. It will be discussed how this thermo-optical property couples to the structural arrest designated as one of the characteristics of the solidification process of polymers.

The exotic ground state of the decorated honeycomb lattice

The study is focusing on the exploration of the magnetic properties of the frustrated decorated honeycomb lattices. The presence of geometrical frustration and C3 symmetry leads to an exotic ground state. Monte Carlo simulations and analytical calculations are used to analyze the system’s behavior. The dependence of the magnetization on the external field of the Ising model exhibits a step-like behavior, while the magnetization of the classical Heisenberg model has no plateau in the isotropic case. An efficient Hamiltonian is proposed to describe the properties of this system on the unfrustrated hexagonal lattice within the framework of the chiral Potts model. Within a specific range of fields, the state of the effective Hamiltonian aligns with that of the original Hamiltonian. The ground state configurations and degeneracy of the system are explored, revealing fractured stripe patterns separated by spins with opposite orientations. These findings contribute to the knowledge of the properties of decorated lattices, offering valuable insights for potential experimental and practical applications.

Unusual step-like stress flow behavior and mechanisms of a 1.3 GPa grade medium-Mn steel with 51.2 % ductility

A Fe-8.9Mn-1.59Si-1.0Al-0.25C medium-Mn steel have achieved a superior combination of strength and ductility, i.e., the product of strength and elongation (PSE) of 66.5 GPa%. Meanwhile, an unusual step-like stress–strain curve due to heterogeneous deformation bands including Lüders band and multiple Portevin–Le Chatelier (PLC) bands was investigated systematacially. The repeated heterogeneous deformation is due to a combination of extrinsic and intrinsic factors. The former refers a small stress concentration near the grip ends of the tensile sample, and the latter is associated with low density of initial mobile dislocations, limited capacity of mobile dislocation multiplication and the presence of meta-stable austenite. As for meta-stable austenite, stress-assisted martensite transformation (SAMT) was confirmed experimentally, which will facilitate strain concentration and the starting of heterogeneous deformation. Moreover, before strain-induced martensite transformation (SIMT), it is the plastic deformation of austenite grains through the slip of partial dislocation and stacking faults (SFs) that contributes to a larger Lüders strain. Finally, we propose that whether it is possible to make the heterogeneous deformation to be a positive side for certain working conditions, which may open new doors for the application of medium-Mn steels. We will continue to do some exploratory studies in this direction next.

Spontaneous Magnetization in the Finite-Size Two-Leg Ising Ladder in the External Magnetic Field

This paper considers a finite-sized two-leg ladder of spin-1/2 particles with local inter-chain Ising interaction. We include the effects of an external magnetic field by incorporating a Zeeman-type coupling between the magnetic field and the spins localized on the lattice sites. To analyze the system, we utilize the transfer-matrix formalism to calculate the partition function. We compute the magnetization for different configurations by varying the system's parameters. We observe the presence 3of spontaneous magnetization within the system. As the inter-chain Ising interaction changes its sign, the magnetization value changes from negative to positive values. Furthermore, we identify a phase transition from diamagnetic to ferromagnetic states when examining the temperature dependence of the magnetization at zero magnetic fields. We observe a step-like behavior in the magnetization curve in the low temperature limit.

Giant dielectric constant, magnetocaloric effect and spin-phonon coupling in EuTbCoMnO6 semiconductor

Transport, dielectric, magnetic and Raman studies of polycrystalline double perovskite EuTbCoMnO6 have been performed. Temperature-dependent resistivity follows the variable range and small polaron hopping mechanism. The temperature-dependent dielectric study shows the usual frequency-dependent step-like behavior. It also shows thermally activated relaxor peak in loss curves with giant dielectric constant near room temperature. The temperature-dependent magnetization demonstrates a second-order phase transition around 113 K. The critical behavior near the magnetic transition has been systematically investigated. The Widom scaling relation and magnetic entropy change calculation have verified the reliability of critical parameters. Maximum magnetic entropy change around the magnetic transition temperature shows the magnetocaloric effect. The estimated values of critical parameters are close to the value of the theoretical mean-field model. Temperature-dependent Raman study shows spin-phonon coupling in the system. The appearance of the magnetocaloric effect and colossal dielectric constant shows that these materials are interesting for real-life applications.

Evaluation of the Number of Degrees of Freedom of the Field Scattered by a 3D Geometry.

The solution to an ill-posed linear inverse problem requires the use of regularization methods to achieve a stable approximation solution. One powerful approach is the truncated singular value decomposition (TSVD), but it requires an appropriate choice of the truncation level. One suitable option is to take into account the number of degrees of freedom (NDF) of the scattered field, which is defined by the step-like behavior of the singular values of the relevant operator. Then, the NDF can be estimated as the number of singular values preceding the knee or the exponential decay. Therefore, an analytical estimation of the NDF is significant for obtaining a stable, regularized solution. This paper addresses the analytical estimation of the NDF of the field scattered by the surface of a cube geometry for a single frequency and the multi-view case in the far-zone. In addition, a method is proposed to find the minimum numbers of plane waves and their directions to achieve the total estimated NDF. The main results are that the NDF is related to the measure of the surface of the cube and can be achieved by only considering a limited number of impinging plane waves. The efficiency of the theoretical discussion is demonstrated through a reconstruction application for microwave tomography of a dielectric object. Numerical examples are provided to confirm the theoretical results.

Phase Instability, Oxygen Desorption and Related Properties in Cu-Based Perovskites Modified by Highly Charged Cations

The rock-salt ordered A2CuWO6 (A = Sr, Ba) with I4/m space group and disordered SrCu0.5M0.5O3−δ (M = Ta, Nb) with Pm3m space group perovskites were successfully obtained via a solid-state reaction route. Heat treatment of Ba2CuWO6 over 900 °C in air leads to phase decomposition to the barium tungstate and copper oxide. Thermogravimetric measurements reveal the strong stoichiometric oxygen content and specific oxygen capacity (ΔWo) exceeding 2.5% for Ba2CuWO6. At the same time, oxygen content reveals Cu3+ content in SrCu0.5Ta0.5O3−δ. Under the following reoxidation of Ba2CuWO6, step-like behavior in weight changes was observed, corresponding to possible Cu+ ion formation at 900 °C; in contrast, no similar effect was detected for M5+ cations. The yellow color of Ba2CuWO6 enables to measure the band gap 2.59 eV. SrCu0.5Ta0.5O3−δ due to high oxygen valance concentration has a low thermal conductivity 1.28 W·m−1·K−1 in the temperature range 25–400 °C.

Dynamics of lattice random walk within regions composed of different media and interfaces

We study the lattice random walk dynamics in a heterogeneous space of two media separated by an interface and having different diffusivity and bias. Depending on the position of the interface, there exist two exclusive ways to model the dynamics: (a) Type A dynamics whereby the interface is placed between two lattice points, and (b) Type B dynamics whereby the interface is placed on a lattice point. For both types, we obtain exact results for the one-dimensional generating function of the Green’s function or propagator for the composite system in unbounded domain as well as domains confined with reflecting, absorbing, and mixed boundaries. For the case with reflecting confinement in the absence of bias, the steady-state probability shows a step-like behavior for the Type A dynamics, while it is uniform for the Type B dynamics. We also derive explicit expressions for the first-passage probability and the mean first-passage time, and compare the hitting time dependence to a single target. Finally, considering the continuous-space continuous-time limit of the propagator, we obtain the boundary conditions at the interface. At the interface, while the flux is the same, the probability density is discontinuous for Type A and is continuous for Type B. For the latter we derive a generalized version of the so-called leather boundary condition in the appropriate limit.

Controlling quantum effects in enhanced strong-field ionisation with machine-learning techniques

We study non-classical pathways and quantum interference in enhanced ionisation of diatomic molecules in strong laser fields using machine learning techniques. Quantum interference provides a ‘bridge’, which facilitates intramolecular population transfer. Its frequency is higher than that of the field, intrinsic to the system and depends on several factors, for instance the state of the initial wavepacket or the internuclear separation. Using dimensionality reduction techniques, namely t-distributed stochastic neighbour embedding and principal component analysis, we investigate the effect of multiple parameters at once and find optimal conditions for enhanced ionisation in static fields, and controlled ionisation release for two-colour driving fields. This controlled ionisation manifests itself as a step-like behaviour in the time-dependent autocorrelation function. We explain the features encountered with phase-space arguments, and also establish a hierarchy of parameters for controlling ionisation via phase-space Wigner quasiprobability flows, such as specific coherent superpositions of states, electron localisation and internuclear-distance ranges.

Моделювання перколяційної поведінки властивостей полімерних нанокомпозитів, наповнених вуглецевими нанотрубками

The paper considers the application of the scaling approach of the percola-tion theory to describe the step-like change in electrical and thermal conductivi-ty of polymer nanocomposites containing carbon nanotubes. In connection with the use of nano-sized fillers for the creation of polymer composite materials, the problem of mathematical description of the behavior of the properties of such systems at critical filling has arisen. The increasing difficulty of describing a sudden change in properties is due to the fact that the described phenomena, due to the fluctuating processes of aggregation of nanotubes and the formation of an infinite cluster that permeates the entire volume of the material, are essen-tially critical, and therefore cannot be described by traditional mathematical models. In order to solve the problem considered in the publication, it is pro-posed to use universal scaling equations. In this case, an analogy is used be-tween the behavior of a ferromagnet in an external electric field and the behav-ior of the properties of a polymer nanocomposite with non-zero conductivity when it is critically filled with nanotubes. According to the above analogy, a number of equations are written to describe the percolation behavior of both electrical conductivity and thermal conductivity of polymer-filler systems. The results of simulation of real data for systems of this type are given and it is shown that the proposed equations allow to describe the step-like behavior of electrical and thermal conductivity of polymer-nanotube systems with high ac-curacy. The critical exponents of the scaling equations were determined and the behavior of the properties when these indices were varied was modeled. When describing the section of the graph before the percolation threshold, the increase in critical exponents leads to an increase in conductivity, while in the section after the percolation threshold, the increase in critical exponents leads to a de-crease in conductivity

An unusual magnetic phenomenon in Mg doping [(CH3)2NH2] CoxMg1−x[HCOO]3 frameworks

In this study, Mg doping metal-organic frameworks (MOFs) [(CH3)2NH2] Co1−x Mg x [HCOO]3 single crystals were synthesized by solvothermal method with normal ratios x = 0, 0.1, 0.2, 0.3, 0.4, 0.6. Powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) results showed that Mg ion is uniformly doped into Co-based MOFs crystal. With the increase of diamagnetic magnesium ions doping, the antiferromagnetic phase transition temperature of Co-based MOFs for pure Co-MOF decreased from 15 K to 7.5 K for x = 0.4. Abnormal larger magnetic hysteresis was obtained for Mg doping crystals with a large coercive field 3100 Oe (x = 0.1), 3700 Oe (x = 0.2), 2900 Oe (x = 0.3) compared with 600 Oe coercive field for pure Co-MOFs (x = 0). At the same time, step-like behavior was first observed on Mg2+ doping sample with x = 0.1–0.3. This unusual magnetic phenomenon is well interpreted based on the coexistence of long-range canted antiferromagnetic order and isolated single-ion quantum magnets. The diamagnetic magnesium ions doping decreases the strong exchange coupling between neighboring Co ions and step-like behavior stemmed from the quantum tunneling of isolated Co ions.

Step-like current–voltage thin-film transistors with amorphous SiZnSnO/SiInZnO/SiZnSnO multilayered-channels

• Observation of step-like transfer curves (I-V) • The organic barrier layer is replaced by inorganic (SIZO) material in this work. • Only amorphous semiconductors (inorganic materials) were used to obtain the step-like behaviour in the IV characteristics. • This study will be beneficial for the recent application of multi-value logic (MVL) circuits. Multi-valued logic (MVL) is a critical approach for high-density information and next-generation digital electronics. Recently developed multilayered-channel structure electronic devices provide new transistor operation of multi-valued logic switching characteristics. This paper investigates the step-like transfer curves of the amorphous SiZnSnO/SiInZnO/SiZnSnO (a-SZTO/SIZO/SZTO or a-SSS) multilayered-channel thin-film transistors (TFTs). The step-like transfer curves of a-SSS TFTs can be tuned intentionally by varying the thickness of the top and bottom layers of a-SZTO mainly because a low conducting material is introduced as a barrier layer to separate the top and bottom layers to obtain the intermediate states. Additionally, the conducting nature of the middle/barrier layer of a-SIZO was varied and studied for different Si concentrations.

Landau–Zener transition with energy-dependent decay rate of the excited state

A remarkable feature of the Landau–Zener transition is insensitivity of the survival probability to the decay rate, τ−1, of the excited state. Namely, the probability for a particle which is initially (at t→−∞) in the ground state to remain at t→∞ in the same state is insensitive to τ−1 which is due to e.g. coupling to continuum (Akulin and Schleich, 1992). This insensitivity was demonstrated for the case when the density of states in the continuum is energy-independent. We study the opposite limit when the density of states in the continuum is a step-like function of energy. As a result of this step-like behavior of the density of states, the decay rate of a driven excited level experiences a jump as a function of time at certain moment t0. We take advantage of the fact that the analytical solution at t<t0 and at t>t0 is known. We show that the decay enters the survival probability when t0 is comparable to the transition time.

Steplike anomalous Hall behaviors in mixed-phase BiFeO3-based heterostructure

The heterostructures based on multiferroic BiFeO3 (BFO) have received much attention for the great potential in magnetoelectric coupling and spintronic applications. Therefore, the BFO films combined with rhombohedral (R) phase and tetragonal (T) phase can bring in various functionalities. Here, we demonstrate that the Ta/Pt/Co/Pt multilayers grown on R-, T-, and mixed-phase BFO exhibit perpendicular magnetic anisotropy. We find that the magnetic switching behavior of the multilayer is sensitive to the phase of the BFO layer. The Ta/Pt/Co/Pt layers grown on top of the pure R- or T-phase BFO show one-step anomalous Hall effect (AHE) switching. However, the layers grown on the mixed-phase BFO show steplike AHE switching. We attribute that the steplike switching behavior originates from the two different interfacial situations between mixed-phase BFO and above layers. Our results bring a potential avenue for realizing spintronic devices based on mixed-phased BFO.

Enhanced Spin Transfer Torque in Single Barrier Model Tunnel Junctions Containing Disordered Interface

We investigate the role of magnetic impurities in the barrier region in enhancing the torque transferred to the free ferromagnet layer in a non-collinear model tunnel junction. The tunnel junction is modeled using the non-equilibrium Green’s function formalism within the tight-binding approximation. The position of the impurity which is described by the single impurity Anderson model is found to have a profound impact on the trends observed in the spin transfer torque. The parallel ([Formula: see text]) torque is observed to have a switch on-off step-like bias behavior while the perpendicular ([Formula: see text]) torque exhibits a change in sign between the switch-on bias voltages. The spin transfer torque is found to be dramatically enhanced when the impurity is positioned at the interface of a five-layer barrier which is three orders of magnitude larger even at temperatures as high as 200[Formula: see text]K. With this formulation the effect of Coulomb repulsion at the impurity site on the torque could be deduced and the obtained results are explained in terms of the region-wise electronic density of states in the junction.

Ratchetlike motion of helical bilayers induced by boundary constraints.

We show that application of boundary constraints generates unusual folding behaviors in responsive (swellable) helical bilayer strips. Unlike the smooth folding trajectories typical of free helical bilayers, the boundary-constrained bilayers exhibit intermittent folding behaviors characterized by rapid, steplike movements. We experimentally study bilayer strips as they swell and fold, and we propose a simple model to explain the emergence of ratchetlike behavior. Experiments and model predictions are then compared to simulations, which enable calculation of elastic energy during swelling. We investigate the dependence of this steplike behavior as a function of elastic boundary condition strength, strip length, and strip shape; interestingly, "V-shape" strips with the same boundary conditions fold smoothly.

Tomonaga-Luttinger Spin Liquid and Kosterlitz-Thouless Transition in the Spin-1/2 Branched Chains: The Study of Topological Phase Transition.

In the present work, we provide a comprehensive numerical investigation of the magnetic properties and phase spectra of three types of spin-1/2 branched chains consisting of one, two and three side spins per unit block with intra-chain interaction and a uniform inter-chain interaction in the presence of an external magnetic field. In a specific magnetic field interval, the low-temperature magnetization of these chains shows a step-like behavior with a pronounced plateau depending on the strength and the type of intra-chain interaction being ferromagnetic or antiferromagnetic. We demonstrate that when inter-chain interaction is antiferromagnetic and intra-chain interaction is ferromagnetic, the magnetization of the models manifests a smooth increase without a plateau, which is evidence of the existence of a Luttinger-like spin liquid phase before reaching its saturation value. On the other hand, when is ferromagnetic and is antiferromagnetic, the low-temperature magnetization of the chain with two branches shows an intermediate plateau at one-half of the saturation magnetization that breaks a quantum spin liquid phase into two regions. The magnetization of the chain with three branches exhibits two intermediate plateaus and two regions of a quantum spin liquid. We demonstrate that the chains with more than one side spin illustrate in their ground-state phase diagram a Kosterlitz–Thouless transition from a gapful phase to a gapless spin liquid phase.