Two-dimensional System Research Articles

Concentration Quenching of Fluorescence Decay Kinetics of Molecular Systems.

Fluorescence concentration quenching occurs when increasing molecular concentration of fluorophores results in a decreasing fluorescence quantum yield. Even though this phenomenon has been studied for decades, its mechanisms and signatures are not yet fully understood. The complexity of the problem arises due to energy migration and trapping in huge networks of molecules. Most of the available theoretical work focuses on integral quantities like fluorescence quantum yield and mean excitation lifetime. In this work, we present a numerical study of the fluorescence decay kinetics of three-dimensional and two-dimensional molecular systems. We investigate the differences arising from the variations in models of trap formations. We also analyze the influence of the molecular orientations to the fluorescence decay kinetics. We compare our results to the well-known analytical models and discuss their ranges of validity. Our findings suggest that the analytical models can provide inspiration for different ways of approximating the fluorescence kinetics, yet more detailed analysis of the experimental data should be done by comparison with numerical simulations.

Magic-angle twisted bilayer graphene under orthogonal and in-plane magnetic fields

We investigate the effect of a magnetic field on the band structure of bilayer graphene with a magic twist angle of 1.08∘. The coupling of a tight-binding model and the Peierls phase allows the calculation of the energy bands of periodic two-dimensional systems. For an orthogonal magnetic field, the Landau levels are dispersive, particularly for magnetic lengths comparable to or larger than the twisted bilayer cell size. A high in-plane magnetic field modifies the low-energy bands and gap, which we demonstrate to be a direct consequence of the minimal coupling.

Two-dimensional rheo-optical measurement system to study dynamics and structure of complex fluids

Abstract We have developed a novel rheo-optical measurement system based on two-dimensional polarization analysis, which can evaluate the rheological properties and structure of a complex fluid simultaneously. To assess the utility of the system, we used it to investigate the relationship between yield behavior and structural evolution in a TEMPO-oxidized cellulose nanofiber (T-CNF) suspension, which is a yield-stress fluid that has been actively studied in recent years. To analyze the structural evolution of a T-CNF suspension, stress-ramp tests were conducted. A two-step yield behavior was observed, and distributions of retardation and orientation axis varied dramatically with increasing shear stress. In particular, different distributions were observed in the three regions: after the first yield point, before the second yield point, and after the second yield point. In experiments with a low-concentration T-CNF suspension that exhibits no yield behavior, the retardation increased monotonically with increasing shear stress, and its distribution was uniform. It was demonstrated that the yield behavior and related structures can be analyzed from these results. More detailed structural mechanisms require various rheological tests using the developed system. However, the present insights demonstrate the valuable information provided by the developed rheo-optical measurement system, contributing essential knowledge for applications in various fields.

Two-Dimensional System of Moment Equations and Macroscopic Boundary Conditions Depending on the Velocity of Movement and the Surface Temperature of a Body Moving in Fluid

This article is dedicated to the derivation of a two-dimensional system of moment equations depending on the velocity of movement and the surface temperature of a body submerged in fluid, and macroscopic boundary conditions for the system of moment equations approximating the Maxwell microscopic boundary condition for the particle distribution function. The initial-boundary value problem for the Boltzmann equation with the Maxwell microscopic boundary condition is approximated by a corresponding problem for the system of moment equations with macroscopic boundary conditions. The number of moment equations and the number of macroscopic boundary conditions are interconnected and depend on the parity of the approximation of the system of moment equations. The setting of the initial-boundary value problem for a non-stationary, nonlinear two-dimensional system of moment equations in the first approximation with macroscopic boundary conditions is presented, and the solvability of the above-mentioned problem in the space of functions continuous in time and square-integrable in spatial variables is proven.

Exploring the effects of a one-dimensional periodic potential on a three-dimensional topological insulator

High mobility two-dimensional systems with superposed 1D lateral periodic potentials exhibit characteristic commensurability (Weiss) oscillations that reflect the interplay of the cyclotron radius at the Fermi level and the superlattice period. Here, we impose a one-dimensional periodic potential on strained HgTe, which is a strong 3D topological insulator. By tuning the Fermi level with top gates, the effects of the artificial potential can be studied in the bulk gap, where only Dirac surface states exist, in the conduction band, and in the valence band, where Dirac electrons and holes coexist. On the electron side, we observe clear commensurability oscillations whose period is governed by the carrier density of the top-surface Dirac electrons. Unexpectedly, weak commensurability oscillations are also observed in the valence band with a period that depends on both electron and hole density. Published by the American Physical Society 2024

A quantum critical Bose gas of magnons in the quasi-two-dimensional antiferromagnet YbCl3 under magnetic fields

AbstractBose–Einstein condensation (BEC) is a quantum phenomenon in which a macroscopic number of bosons occupy the lowest energy state and acquire coherence at low temperatures. In three-dimensional antiferromagnets, a magnetic-field-induced transition has been successfully described as a magnon BEC. For a strictly two-dimensional (2D) system, it is known that BEC cannot take place due to the presence of a finite density of states at zero energy. However, in a realistic quasi-2D magnet consisting of stacked magnetic layers, a small but finite interlayer coupling stabilizes marginal BEC but such that 2D physics is still expected to dominate. This 2D-limit BEC behaviour has been reported in a few materials but only at very high magnetic fields that are difficult to access. The honeycomb S = 1/2 Heisenberg antiferromagnet YbCl3 exhibits a transition to a fully polarized state at a relatively low in-plane magnetic field. Here, we demonstrate the formation of a quantum critical 2D Bose gas at the transition field, which, with lowering the field, experiences a BEC marginally stabilized by an extremely small interlayer coupling. Our observations establish YbCl3, previously a Kitaev quantum spin liquid material, as a realization of a quantum critical BEC in the 2D limit.

Analyses of the SIR Epidemic Model Including Treatment and Immigration

This paper aims to examine the dynamics of a variation of a nonlinear SIR epidemic model. We analyze the complex dynamic nature of the discrete-time SIR epidemic model by discretizing a continuous SIR epidemic model subject to treatment and immigration effects with the Euler method. First of all, we show the existence of equilibrium points in the model by reducing the three-dimensional system to the two-dimensional system. Next, we show the stability conditions of the obtained positive equilibrium point and the visibility of flip bifurcation. A feedback control strategy is applied to control the chaos occurring in the system after a certain period of time. We also perform numerical simulations to support analytical results. We do all these analyses for models with and without immigration and show the effect of immigration on dynamics.

Spin disorder control of topological spin texture

Stabilization of topological spin textures in layered magnets has the potential to drive the development of advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation of the topological spin textures beyond skyrmion in a two-dimensional magnet system remains challenging. Here, we demonstrate the introduction of magnetic iron atoms between the van der Waals gap of a layered magnet, Fe3GaTe2, to modify local anisotropic magnetic interactions. Consequently, we present direct observations of the order-disorder skyrmion lattices transition. In addition, non-trivial topological solitons, such as skyrmioniums and skyrmion bags, are realized at room temperature. Our work highlights the influence of random spin control of non-trivial topological spin textures.

Structural complexity of snapshots of two-dimensional Fermi-Hubbard systems

Structural complexity of snapshots of two-dimensional Fermi-Hubbard systems

Interaction-controlled transport in a two-dimensional massless-massive Dirac system: Transition from degenerate to nondegenerate regimes

Interaction-controlled transport in a two-dimensional massless-massive Dirac system: Transition from degenerate to nondegenerate regimes

Realization of fractional quantum Hall state with interacting photons.

Fractional quantum Hall (FQH) states are known for their robust topological order and possess properties that are appealing for applications in fault-tolerant quantum computing. An engineered quantum platform would provide opportunities to operate FQH states without an external magnetic field and enhance local and coherent manipulation of these exotic states. We demonstrate a lattice version of photon FQH states using a programmable on-chip platform based on photon blockade and engineering gauge fields on a two-dimensional circuit quantum electrodynamics system. We observe the effective photon Lorentz force and butterfly spectrum in the artificial gauge field, a prerequisite for FQH states. After adiabatic assembly of Laughlin FQH wave function of 1/2 filling factor from localized photons, we observe strong density correlation and chiral topological flow among the FQH photons. We then verify the unique features of FQH states in response to external fields, including the incompressibility of generating quasiparticles and the smoking-gun signature of fractional quantum Hall conductivity. Our work illustrates a route to the creation and manipulation of novel strongly correlated topological quantum matter composed of photons and opens up possibilities for fault-tolerant quantum information devices.

Synthesis and characterisation of Cu2Ge, a new two-dimensional Dirac nodal line semimetal

Abstract Dirac nodal line semimetals are a novel class of topological materials in which the valence and conduction bands touch along lines in the reciprocal space, with linear dispersion. These materials attract a growing attention, but the experimental realizations for two-dimensional systems are sparse. We report here the first experimental realization of a two-dimensional hexagonal monolayer
Cu2Ge, grown by evaporation of Ge on a Cu(111) substrate. Through a combination of LEED, XPS and ARPES measurements, we show that the surface presents all characteristics expected from calculations for a free-standing Cu2Ge monolayer. More specifically, the preservation of the two concentric nodal lines around the Γ point indicates weak interactions between the Cu2Ge surface and its Cu(111) substrate, making it an ideal system for the study of Dirac nodal line materials.

Optical Shubnikov–de Haas oscillations in two-dimensional electron systems

Optical Shubnikov–de Haas oscillations in two-dimensional electron systems

A new dynamic Monte Carlo method satisfying n-particle diffusion equation with position-dependent diffusion coefficient, free energy, and intermolecular interactions.

A dynamic Monte Carlo (MC) method recently proposed by us [Nagai et al., J. Chem. Phys. 156, 154506 (2022)] to describe single-particle diffusion of a molecule in a heterogeneous space with position-dependent diffusion coefficient and free energy is generalized here to n-particle dynamics, where n molecules diffuse in heterogeneous media interacting via their intermolecular potential. Starting from the master equation, we give an algebraic proof that the dynamic MC transition probabilities proposed here produce particle trajectories that satisfy the n-particle diffusion equation with position-dependent diffusion coefficient D0i(ri), free energy F1i(ri), and intermolecular interactions Vij(ri, rj). The MC calculations based on this method are compared to molecular dynamics (MD) calculations for two-dimensional heterogeneous Lennard-Jones test systems, showing excellent agreement of the long-distance global diffusion coefficient between the two cases. Thus, the particle trajectories produced by the present MC transition probabilities satisfy the n-particle diffusion equation, and the diffusion equation well describes the long-distance trajectories produced by the MD calculations. The method is also an extension of the conventional equilibrium Metropolis MC calculation for homogeneous systems with a constant diffusion coefficient to the dynamics in heterogeneous systems with a position-dependent diffusion coefficient and potential. In the present method, interactions and dynamics of the real systems are coarse-grained such that the calculation cost is drastically reduced. This provides an approach for the investigation of particle dynamics in very complex and large systems, where the diffusing length is of sub-micrometer order and the diffusion time is of the order of milliseconds or more.

Metal-organic frameworks as an active substrate for cell-interaction studies and cell-on-a-chip platforms

Metal-organic frameworks (MOFs) are an emerging class of materials with immense biomedical potential for their unique interactions with biological and organic materials. In this work, we select two candidate two-dimensional (2D) MOF systems based on Fe3+ and Ni2+ metal centers and 2-aminoterephthalate acid ligand (Fe-MOF and Ni-MOF) and evaluate their performance as an active interface for study of cell-interactions. 2D Fe-MOF and Ni-MOF were synthesized onto hydroxyl-modified gold and glass substrates using a layer-by-layer liquid-phase-epitaxy (LbL-LPE) growth at room temperature and used as active substrates (Fe-MOF/glass, Fe-MOF/Au, Ni-MOF/glass and Ni-MOF/Au, respectively) for MTT cell-proliferation and reactive oxygen species tests using the PC-12 cell-line in order to investigate the biocompatibility. Immunostaining and morphological analyses of PC-12 cells on MOF interfaces suggested a stronger cell-substrate interaction in comparison to glass and were further characterized using the Electrical Cell-substrate Impedance Sensing (ECIS) technique, here for the first time, employed to study cell attachment, spreading and proliferation on 2D Fe-MOF. The 2D Fe-MOF showed superior long-term stability in cell culture medium by recording impedance over 24 hours, crucial to monitor cell-dynamics at a solid-liquid interface. A significant increase of interfacial impedance was observed in ECIS, due to PC-12 cells adhering onto 2D Fe-MOF, which was also confirmed by the focused ion beam etching followed by scanning electron microscopy. Our novel findings, therefore, suggest 2D MOFs as highly suitable platform for the study of cell-related interactions using electrical techniques and potentially pave the way for future use of MOFs for bioelectronics and biosensor applications.

In vitro proliferation and differentiation of mouse spermatogonial stem cells in decellularized human placenta matrix.

Utilizing natural scaffold production derived from extracellular matrix components presents a promising strategy for advancing in vitro spermatogenesis. In this study, we employed decellularized human placental tissue as a scaffold, upon which neonatal mouse spermatogonial cells (SCs) were cultured three-dimensional (3D) configuration. To assess cellular proliferation, we examined the expression of key markers (Id4 and Gfrα1) at both 1 and 14 days into the culture. Our quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed a notable increase in Gfrα1 gene expression, with the 3D culture group exhibiting the highest levels. Furthermore, the relative frequency of Gfrα1-positive cells significantly rose from 38.1% in isolated SCs to 46.13% and 76.93% in the two-dimensional (2D) and 3D culture systems, respectively. Moving forward to days 14 and 35 of the culture period, we evaluated the expression of differentiating markers (Sycp3, acrosin, and Protamine 1). Sycp3 and Prm1 gene expression levels were upregulated in both 2D and 3D cultures, with the 3D group displaying the highest expression. Additionally, acrosin gene expression increased notably within the 3D culture. Notably, at the 35-day mark, the percentage of Prm1-positive cells in the 3D group (36.4%) significantly surpassed that in the 2D group (10.96%). This study suggests that the utilization of placental scaffolds holds significant promise as a bio-scaffold for enhancing mouse in vitro spermatogenesis.

Hydrodynamic characterization of bubble column using Dynamical High Order Decomposition approach

Bubble columns play a crucial role in a wide range of industries, including chemical and biochemical processes, petrochemicals, and environmental engineering. Understanding the dynamics of bubble columns is essential for optimizing their performance in various applications. This study proposes a data-driven approach for analyzing the dynamics of a two-dimensional bubble column system. We conducted simulations with varying superficial velocities and generated a comprehensive training dataset encompassing the entire velocity and pressure fields to achieve this. We then compared the performance of two approaches, the Fast Fourier Transformation (FFT) and the High-Order Dynamic Mode Decomposition (HODMD), in representing the system’s dynamics. Our findings demonstrate that the conventional FFT approach fails to adequately capture the complex dynamics of the dispersed multiphase flow system. This limitation arises due to the distribution of frequencies along the domain. Conversely, our work highlights the success of the HODMD method in accurately representing the system’s dynamics using only a few arbitrary sampling points within the domain. The implications of this study are significant, as it sheds light on the potential benefits of employing HODMD for analyzing bubble column dynamics. By utilizing this approach, industrial processes can be optimized more effectively across various applications.

Nonlinear helicity anomalies in the cyclotron resonance photoresistance of two-dimensional electron systems

Nonlinear helicity anomalies in the cyclotron resonance photoresistance of two-dimensional electron systems

Nonintegrability of time-periodic perturbations of single-degree-of-freedom Hamiltonian systems near homo- and heteroclinic orbits

We consider time-periodic perturbations of single-degree-of-freedom Hamiltonian systems and study their real-meromorphic nonintegrability in the Bogoyavlenskij sense using a generalized version due to Ayoul and Zung of the Morales-Ramis theory. The perturbation terms are assumed to have finite Fourier series in time, and the perturbed systems are rewritten as higher-dimensional autonomous systems having the small parameter as a state variable. We show that if the Melnikov functions are not constant, then the autonomous systems are not real-meromorphically integrable near homo- and heteroclinic orbits. Our result is not just an extension of previous results for homocliic orbits to heteroclinic orbits and provides a stronger conclusion than them for the case of homoclinic orbits. We illustrate the theory for two periodically forced Duffing oscillators and a periodically forced two-dimensional system.

A numerical investigation of a well-known nonlinear Newell-Whitehead-Segel equation using the rank polynomial of the star graph

Mathematical models of pattern formation are indispensable tools in various fields, from developmental biology to ecology, providing insights into complex phenomena and contributing to our understanding of the natural world. These patterns have been extensively studied using reaction-diffusion and NewellWhiteheadSegel models. This article intended to find an approximate numerical solution to the NewellWhiteheadSegel equation. The appearance of stripe patterns in two-dimensional systems is explained in nonlinear systems using the NewellWhiteheadSegel equation. Based on the function basis of rank polynomials of star graphs and the well-posed operational matrices, the rank polynomial collocation method is constructed. The alleged rank polynomial collocation method created a system of nonlinear algebraic equations from the nonlinear NewellWhiteheadSegel equation. The nonlinear NewellWhiteheadSegel equation solution is approximated by solving the resulting system via Newton’s Raphson method. Numerical instances are provided to illustrate the validity and effectiveness of the technique. Verification of accuracy is accomplished by calculating error norms. The obtained numerical results show a reasonable degree of consistency with the findings reported in the current literature. The scheme’s primary benefit is the algorithm’s ease of implementation.