Two-dimensional System Research Articles

Selective damping of plasmons in coupled two-dimensional systems by Coulomb drag

Selective damping of plasmons in coupled two-dimensional systems by Coulomb drag

Probing chiral-symmetric higher-order topological insulators with multipole winding number

The interplay between crystalline symmetry and band topology gives rise to unprecedented lower-dimensional boundary states in higher-order topological insulators (HOTIs). However, the measurement of the topological invariants of HOTIs remains a significant challenge. Here, we define a multipole winding number (MWN) for chiral-symmetric HOTIs by applying a corner twisted boundary condition. The MWN, arising from both bulk and boundary states, accurately captures the bulk-corner correspondence including boundary-obstructed topological phases. To address the measurement challenge, we leverage the perturbative nature of the corner twisted boundary condition and develop a real-space approach for determining the MWN in both two-dimensional and three-dimensional systems. The real-space formula provides an experimentally viable strategy for directly probing the topology of chiral-symmetric HOTIs through dynamical evolution. Our findings not only highlight the twisted boundary condition as a powerful tool for investigating HOTIs, but also establish a paradigm for exploring real-space formulas for the topological invariants of HOTIs.

A novel multi-delay feedback digital chaos anti-degradation algorithm and its application in key generator

Abstract Under conditions of finite accuracy, chaotic systems will exhibit a sequence of dynamic degradation issues. Such chaotic systems cannot be considered strictly chaotic, and their applications will be significantly impacted. A control approach is given to handle this problem, which combines parameter perturbation and multi-delay dynamic feedback. This approach utilizes a pseudo-random sequence produced by a high-performance chaotic system to disturb the parameters, then loops back the output of the previous state to the input based on its activity. Numerical studies were conducted to verify the usefulness of this enhanced technique when used in both one-dimensional and two-dimensional chaotic systems. Using a two-dimensional chaotic system as an example, it was confirmed that the enhanced digital chaotic system is extremely responsive to little variations in the starting value. Subsequently, a key generator was created, which successfully passed the NIST randomness test. The experimental results demonstrate that the enhanced digital chaotic system has favorable chaotic properties within the constraints of low precision.

Unconventional quantum oscillations and evidence of nonparabolic electronic states in quasi-two-dimensional electron system at complex oxide interfaces

The simultaneous occurrence of electric-field controlled superconductivity and spin-orbit interaction makes two-dimensional electron systems (2DES) constructed from perovskite transition metal oxides promising candidates for the next generation of spintronics and quantum computing. It is, however, essential to understand the electronic bands thoroughly and verify the predicted electronic states experimentally in these 2DES to advance technological applications. Here, we present insights into the electronic states of the 2DES at oxide interfaces through comprehensive investigations of Shubnikov–de Haas oscillations in three different systems: EuO/KTaO3, LaAlO3/SrTiO3, and amorphous-LaAlO3/KTaO3. To accurately resolve these oscillations, we conducted transport measurements in high magnetic fields up to 60 T and low temperatures down to 100 mK. For 2D confined electrons at these interfaces, we observed a progressive increase of oscillations frequency and cyclotron mass with the magnetic field. We interpret these universal and intriguing findings by considering the existence of nontrivial electronic bands, for which the E−k dispersion incorporates both linear and parabolic relations. In addition to providing experimental evidence for nonparabolic electronic states in KTaO3 and SrTiO3 2DES, the unconventional oscillations presented in this study establish a paradigm for quantum oscillations in 2DES based on perovskite transition metal oxides, where the oscillation frequencies in 1/B exhibit quadratic dependence on the magnetic field. Published by the American Physical Society 2024

Unambiguous simulation of diffusive charge transport in disordered nanoribbons

Charge transport in disordered two-dimensional (2D) systems showcases a myriad of unique phenomenologies that highlight different aspects of the underlying quantum dynamics. Electrons in such systems undergo a crossover from ballistic propagation to Anderson localization, contingent on the system’s effective coherence length. Between the extended and localized phases lies a diffusive crossover in which the charge conductivity is properly defined. The numerical observation of this regime has remained elusive because it requires fully coherent transport to be simulated in systems whose dimensions are sufficiently large to meaningfully split the mean-free path and localization length scales. To address this challenge, we employed a novel linear scaling time-resolved approach that enabled us to derive the dc-transport characteristics and observe the three expected 2D transport regimes — ballistic, diffusive, and localized.

Research on Propagation Characteristics of Fracture Grouting in Clay Formation

Splitting grouting is a highly effective technique for reinforcing tunnels and underground structures, ensuring their operational stability and facilitating long-term maintenance. It has been widely adopted in the prevention and remediation of geological hazards. However, the theoretical research on the diffusion mechanisms of split grouting lags behind its practical applications. This study addresses several key scientific challenges in understanding the diffusion behavior of split grouting. By integrating experimental design, numerical simulations, and theoretical analysis, we conduct a systematic investigation into the diffusion process and vein morphology of split grouting in both homogeneous and heterogeneous formations. We first employed a self-developed two-dimensional grouting test system to perform diffusion experiments on cohesive strata, focusing on the influence of various factors such as grout density, water/cement ratio, soil consistency, and fracture characteristics. The results provide insights into the diffusion patterns, morphology, soil pressure distribution, and surface uplift behavior of the grout veins. Subsequently, a numerical simulation program, developed in-house, based on the finite element method (FEM) and the volume of fluid (VOF) approach, was employed to model the entire process of fracturing grouting within clay strata. The experimental and numerical results indicate that grout vein diffusion in layered soil follows a Y-shaped pattern with an inclined deflection. In uniform strata, the surface uplift curve displays both symmetrical and asymmetrical “convex” elevations, while in heterogeneous soft and hard strata, the uplift is characterized by distinct “convex” deformations. Finally, based on these findings and the principles of contact mechanics, we analyze the underlying mechanisms. The results suggest that weak contact zones undergo tensile cracking and horizontal deflection prior to the formation of grout veins. Additionally, local stress rotations in the soil can induce tilting and deflection. The theoretical insights derived from this study provide valuable guidance for practical engineering applications.

Energy function of 2D and 3D dynamical systems

It is far well-known that energy function of a two-dimensional autonomous dynamical system can be simply obtained by multiplying its corresponding second-order ordinary differential equation, i.e., its equation of motion by the first time derivative of its state variable. In the nineties, one of us (J.C.S.) stated that a three-dimensional autonomous dynamical system can be also transformed into a third-order ordinary differential equation of motion todays known as jerk equation. Although a method has been developed during these last decades to provide the energy function of such three-dimensional autonomous dynamical systems, the question arose to determine by which type of term, i.e., by the first or second time derivative of their state variable, the corresponding jerk equation of these systems should be multiplied to deduce their energy function. We prove in this work that the jerk equation of such systems must be multiplied by the second time derivative of the state variable and not by the first like in dimension two. We then provide an interpretation of the new term appearing in the energy function and called jerk energy. We thus established that it is possible to obtain the energy function of a three-dimensional dynamical system directly from its corresponding jerk equation. Two and three-dimensional Van der Pol models are then used to exemplify these main results. Applications to Lorenz and Chua’s models confirms their validity.

[formula omitted] predictive control for 2-D Roesser model under multiple denial-of-service attacks

In this paper, we concentrate on H∞ predictive control issue for Roesser-type two-dimensional (2-D) system under multiple denial of service attacks (DoSs). The research will be realized through the following considerations. Firstly, a general multi-DOSs description is formulated under Roesser-type 2-D framework. Then the event-based 2-D triggered strategy is constructed to compensate the occurred multiple DoSs network attacks, which helps to save network resources and improve the network utilization. On this basis, some innovative multi-steps 2-D predictive controller is designed, and then, Roesser-type 2-D predictive control system can be obtained accordingly. For the predictive control system, we propose the detailed analysis scheme for considering H∞ predictive control issue. Furthermore, we derive the 2-D controller gain design algorithm, and the H∞ robustness analysis criterion in solvable matrix constraints. To conclude the paper, a chemical process example is given to illustrate the effectiveness and practicability of the provided method and controller design.

PIEZO-dependent mechanosensing is essential for intestinal stem cell fate decision and maintenance.

Stem cells perceive and respond to biochemical and physical signals to maintain homeostasis. Yet, it remains unclear how stem cells sense mechanical signals from their niche in vivo. In this work, we investigated the roles of PIEZO mechanosensitive channels in the intestinal stem cell (ISC) niche. We used mouse genetics and single-cell RNA sequencing analysis to assess the requirement for PIEZO channels in ISC maintenance. In vivo measurement of basement membrane stiffness showed that ISCs reside in a more rigid microenvironment at the bottom of the crypt. Three-dimensional and two-dimensional organoid systems combined with bioengineered substrates and a stretching device revealed that PIEZO channels sense extracellular mechanical stimuli to modulate ISC function. This study delineates the mechanistic cascade of PIEZO activation that coordinates ISC fate decision and maintenance.

Superconductivity in two-dimensional systems enhanced by nonadiabatic phonon-production effects

Superconductivity in two-dimensional systems enhanced by nonadiabatic phonon-production effects

Spin relaxation in persistent spin textures

Abstract Spin relaxation due to the combined diffuse scattering and spin-orbit coupling (SOC) plays a crucial role for the efficient spin transport, which is a prerequisite for spintronic devices. Here, we investigate the spin relaxation in two-dimensional systems with different types of SOC, with a particular focus on the SOC with persistent spin texture (PSO). Based on the Boltzmann transport theory, we calculate spin diffusion matrices within the framework of Dyakonov-Perel mechanism. In the uniform case, it is found that the in-plane and out-of-plane spin relaxations for all considered SOCs are independent. Interestingly, the in-plane spin relaxation for certain PSOs reveals significant anisotropy characterized by the infinite spin relaxation time for the spin oriented along the direction of spin-orbit field. In the non-uniform case, we show that there always exists the static solution for the PSO with SU(2) symmetry, which corresponds the persistent spin helix in real space. Our work is expected to enrich the fundamental understanding of spin relaxation mechanism and provide new guidelines to design spin-orbitronic devices.

Tumor-Infiltration Mimicking Model of Contaminated Ovarian Tissue as an Innovative Platform for Advanced Cancer Research.

The development of advanced preclinical models is crucial for the evaluation and validation of novel therapeutic strategies in oncology. Three-dimensional (3D) microtumor models, which incorporate both cancer and stromal cells within biomimetic hydrogels, have emerged as powerful tools that more accurately replicate the complex tumor microenvironment compared to traditional two-dimensional (2D) cell culture systems. In this context, our study aims to develop 3D microtumor models by integrating cancer and stromal cells within an extracellular-matrix-mimetic hydrogel, as a physiologically accurate microtumor model that can serve as an innovative platform for advanced cancer research and drug screening. Microtumors composed of varying ratios of leukemia cells (HL-60) to healthy ovarian stromal cells (SCs) (1:1, 1:10, 1:100, or 1:1000) were encapsulated in PEGylated fibrin hydrogel and cultured for 5days. The proliferation and dynamics of cancerous and healthy cell populations were evaluated using CD43/Ki67 immunofluorescence double staining. Our findings indicate that tumor development and malignancy progression can be influenced by adjusting cell culture ratios and incubation time. Notably, the HL-60:SCs ratio of 1:100 closely replicated leukemia cell invasion in ovarian tissue, demonstrating detectable malignancy on the third and fifth days without significant changes in total cell density dynamics. This 3D leukemia microtumor model offers superior physiological relevance compared to traditional 2D in vitro assays and shows promising potential for applications in cellular analysis and drug screening.

Multiple Weyl fermions and topological phase transition in two-dimensional ferromagnetic CrS2.

The study of topological states in two-dimensional (2D) systems, especially with magnetic properties, has recently gained significant attention owing to their potential in spintronics and nanotechnology. Here, we propose a 2D ferromagnetic (FM) material, CrS2, which hosts multiple Weyl points (WPs) and can undergo a topological phase transition by rotating the magnetization direction. Based on first-principles calculations, we identify distinct Weyl points around the Fermi level: W1, W2, and W3. These points appear in both spin channels and include various types: type-I, type-II and type-III WPs. Corresponding Fermi arcs are clearly observed at the material edges. CrS2 displays a FM ground state with the easy magnetization direction along the c-axis. When the magnetization direction is rotated in the x-y plane, the W1 and W3 points open gaps, with the gap values remaining the same in all magnetization directions. The W2 can maintain a crossing at specific in-plane magnetization directions, indicating that the material retains its Weyl state. Additionally, we examine the effects of biaxial and uniaxial strains on electronic properties. Weyl points remain stable under biaxial strain of less than ±5%, but they disappear under uniaxial strain. In summary, our work proposes a 2D FM material with multiple coexisting Weyl fermions, where the topological states can be tuned by an external magnetic field.

Equality of Magnetization and Edge Current for Interacting Lattice Fermions at Positive Temperature

We prove that the magnetization is equal to the edge current in the thermodynamic limit for a large class of models of lattice fermions with finite-range interactions satisfying local indistinguishability of the Gibbs state, a condition known to hold for sufficiently high temperatures. Our result implies that edge currents in such systems are determined by bulk properties and are therefore stable against large perturbations near the boundaries. Moreover, the equality persists also after taking the derivative with respect to the chemical potential. We show that this form of bulk-edge correspondence is essentially a consequence of homogeneity in the bulk and locality of the Gibbs state. An important intermediate result is a new version of Bloch’s theorem for two-dimensional systems, stating that persistent currents vanish in the bulk.

Renormalization of Fermi Velocity and Band Gap in a Two-Dimensional System near a Conducting Plate at Finite Temperature

In a recent work, it was demonstrated within the framework of Pseudo Quantum Electro-dynamics (PQED) at zero temperature that the logarithmic renormalization of the Fermi velocity in a graphene sheet is inhibited by the presence of a single parallel conducting plate. In the present study, aiming for a more general and realistic approach, we explore the renormalization of the Fermi velocity and mass (band gap) in a two-dimensional system influenced by a conducting plate at finite temperature, also in the context of PQED. Our findings refine previous results in the literature and provide valuable insights for future investigations on the effects of external conditions within PQED.

Mouse Small Intestinal Organoid Cultures.

The intestinal epithelium is a highly dynamic and self-renewing tissue that is crucial for maintaining gut homeostasis. It can be cultured in vitro from isolated crypts to form three-dimensional (3D) intestinal organoids. These organoids have the ability to proliferate and differentiate into various epithelial cell lineages, offering a more physiologically relevant model compared to traditional two-dimensional (2D) culture systems. Mesenchymal cells, located near epithelial cells, regulate epithelial behavior through paracrine signaling and provide structural support. Building on recent advances in the biology of epithelial and mesenchymal cells, we have developed a coculture system that integrates intestinal organoids with mesenchymal cells. In this system, intestinal organoids are cultured in direct or indirect contact with mesenchymal cells, allowing for the simulation of signal exchange and interactions within the in vivo-like microenvironment. This coculture system not only preserves the 3D architecture of the organoids but also enhances their physiological relevance by introducing cellular complexity. The system is capable of long-term maintenance and is adaptable to a wide range of experimental manipulations. As such, this coculture model serves as a powerful tool for studying the interactions between the intestinal epithelium and its surrounding stroma, providing new insights into stem cell biology, tissue regeneration, and disease mechanisms. Here, we introduce the methods of mouse crypt isolation, intestinal organoid culture, and its coculture with mesenchymal cell.

Quantum Hall effect in a CVD-grown oxide

Two-dimensional (2D) electron systems are promising for investigating correlated quantum phenomena. In particular, 2D oxides provide a platform that can host various quantum phases such as quantized Hall effect, superconductivity, or magnetism. The realization of such quantum phases in 2D oxides heavily relies on dedicated heterostructure growths. Here we show the integer quantum Hall effect achieved in chemical vapor deposition grown Bi2O2Se - a representative member of a more accessible oxide family. A single or few subband 2D electron system can be prepared in thin films of Bi2O2Se, where the film thickness acts as the key subband design parameter and the occupation is determined by the electric field effect. This oxide platform exhibits characteristic advantages in structural flexibility due to its layered nature, making it suitable for scalable growth. The unique small mass distinguishes Bi2O2Se from other high-mobility oxides, providing a new platform for exploring quantum Hall physics in 2D oxides.

New adaptive low-dissipation central-upwind schemes

We introduce new second-order adaptive low-dissipation central-upwind (LDCU) schemes for the one- and two-dimensional hyperbolic systems of conservation laws. The new adaptive LDCU schemes employ the recently proposed LDCU numerical fluxes computed using the point values reconstructed with the help of adaptively selected nonlinear limiters. To this end, we use a smoothness indicator to detect “rough” parts of the computed solution, where the piecewise linear reconstruction is performed using an overcompressive limiter, which leads to extremely sharp resolution of shock and contact waves. In the “smooth” areas, we use a more dissipative limiter to prevent appearance of artificial kinks and staircase-like structures there. In order to avoid oscillations, we perform the reconstruction in the local characteristic variables obtained using the local characteristic decomposition. We use a smoothness indicator from Löhner (1987) [34] and apply the developed schemes to the one- and two-dimensional Euler equations of gas dynamics. The obtained numerical results clearly demonstrate that the new adaptive LDCU schemes outperform the original ones.

Crystal Structure Design and Synthesis of Noncentrosymmetric Superconductors in Intercalation-Induced Transition Metal Dichalcogenides.

In this paper, we have performed a crystal structure screening and properties prediction framework within the noncentrosymmetric AMX2 system, which arises from the intercalation of elements in transition metal dichalcogenides. After rigorous evaluations of thermodynamic and dynamic stability, we have refined our initial structure pool of 504 crystals to a focused set of 48 promising candidates. Analysis of their electronic properties has revealed that 23 of these crystals exhibit semiconducting behavior. The results on electron-phonon coupling and band calculations indicate that most of the remaining 25 crystals are superconducting topological nodal line or Weyl semimetals. Additionally, we find that β-InNbSe2 in the AMX2 family can serve as an excellent candidate to explore topological nodal lines and Lifshitz transitions. Furthermore, we also extended the thermodynamic stability analysis to higher temperatures. Ultimately, we have successfully synthesized β-InNbSe2 with a stoichiometric ratio of 1:1:2 experimentally and characterized its superconducting properties. This study represents a systematic foray into the identification of new superconducting and topological materials within the noncentrosymmetric AMX2 family. This screening framework can be extended to other quasi two-dimensional systems.

Topological one-way edge states in locally resonant metamaterials

The quantum anomalous Hall effect (QAHE) enables dissipation-free motion within its edge states, offering considerable potential for developments in the fields of electronics, phononics, and elastic waves. In this study, we introduce an elastic metamaterial designed to realize the QAHE at low frequencies. Our approach involves deploying a two-dimensional honeycomb spring-mass system on a rotating platform to break time-reversal symmetry via the Coriolis Force and incorporating local resonators to achieve low-frequency topological edge states. We begin by deriving the system’s equations of motion through analytical rigid body dynamics. Subsequently, we apply Bloch wave solutions to establish the dispersion relations and identify the topological edge states. We then conduct numerical simulations to confirm the one-way transmission characteristics of these states. The addition of local resonators not only extends the frequency range of the topological edge states but also lowers the operational frequency of the system. This robust waveguide, capable of one-way transmission, has potential applications in directional transmission, vibration damping, noise reduction, and acoustic imaging.