Journal of Physics: Condensed Matter最新文献

Over the past decade, a new class of ferroelectric materials with atomic-level thickness, particularly monolayer materials, has been predicted theoretically and confirmed experimentally. These two-dimensional ferroelectric materials, especially those exhibiting finite out-of-plane (OOP) polarizations, have garnered significant attention in both condensed matter physics and materials science. On one hand, they offer promising avenues for the miniaturization of ferroelectric devices. On the other hand, they reveal novel physical mechanisms that go beyond those found in conventional bulk ferroelectrics, enabling the emergence of OOP polarization under depolarization fields. Recent studies have identified various mechanisms capable of generating OOP polarization in monolayers, a phenomenon previously considered unlikely in traditional bulk materials like ferroelectric perovskites. This review article highlights the recent advancements in understanding two-dimensional ferroelectricity in monolayer candidates. We focus primarily on the exploration of these unique mechanisms, as investigated and rationalized in recent years. Furthermore, we discuss the promising prospects in this emerging field of ferroelectricity and the bright future of two-dimensional monolayer materials.

A review of the electronic and optical properties of Kekulé and other short wavelength modulations textures on graphene is presented. Starting from the experimental realization of such textures, the review discusses the electronic and optical properties in terms of several theoretical models like the tight-binding Hamiltonian and effective low energy models based on the Dirac equation. Other surveyed subjects are, strain effects, valley engineering, Kekulé bilayers, zitterbewegung, Kekulé interfaces, valley birefringence and the skew valley scattering. Specific signatures in the optical and electronic conductivities of Kekule textures are next discussed using several approaches like linear response theory, the random phase approximation, and Floquet theory. Plasmons are also presented by considering the dielectric function. Finally, a discussion is presented on how Kekulé textures are related with highly correlated phases, including its importance in magic angle twisted bilayer graphene superconductivity and related quantum phases.

The industrialization has severely impacted the ecosystem because of intensive use of chemicals and gases, causing the undesired outcomes such as hazardous gases, e.g. carbon monoxide (CO), nitrous oxide (NO_x), ammonia (NH₃), hydrogen (H₂), hydrogen sulfide (H₂S) and even volatile organic compounds. These hazardous gases are not only impacting the living beings but also the entire ecosystem. Thus, it becomes essential to monitor these gases for their efficient management. There are continuous efforts to realize such sensors, which rely on the functional materials properties. The widely used such sensors use metal oxide nanomaterials. However, these are not very sensitive and operate at higher temperatures. In contrast, two-dimensional (2D) materials such as Graphene, Borophene, MXenes, and transition metal dichalcogenides (TMDs) including doping, functionalization, and heterostructures offer unique physical, chemical, and optoelectronic properties. The chemical properties with high specific surface area of 2D materials make them suitable for gas sensing applications. The present review covers the recent developments on 2D-layered material, including MoS₂, WS₂, h-BN, and Graphene, as well as their heterostructures for gas sensing applications. The review article also emphasizes their synthesis and characterization techniques, especially for 2D materials. The electronic properties of these materials are highly sensitive to any chemical changes, resulting in significant changes in their resistance. It led to the development of the highly scalable chemiresistive-based gas sensor. The sensing parameters such as sensitivity, selectivity, gas concentration, limit of detection, temperature, humidity, response, reproducibility, stability, recovery, and response time are discussed in detail to understand the gas sensing characteristics of these 2D materials. This review also includes the past developments, current status, and future scope of these 2D materials as highly efficient gas sensors. Thus, this review article may lead the researchers to design and develop highly sensitive gas sensors based on 2D materials.

Two-dimensional metal-organic frameworks (MOF) are widely used in electronic devices and energy storage due to their large surface area, abundant active sites, and tunable sizes. A deeper understanding of the thermal transport properties of two-dimensional MOF materials is essential for these applications. In this work, we systematically studied the thermal transport properties of M₃(C₆O₆)₂(M = Fe, Co, Ni) by using a machine learning interatomic potential method combined with the phonon Boltzmann transport equation. The results show that the lattice thermal conductivities of Fe₃(C₆O₆)₂, Co₃(C₆O₆)₂, and Ni₃(C₆O₆)₂at room temperature are 4.0 W mK^-1, 5.5 W mK^-1, and 5.8 W mK^-1, respectively. The differences in thermal conductivity primarily arise from variations in phonon relaxation times, which can be elucidated by examining the three-phonon scattering phase space. Further analysis of bond strengths reveals that the strong bonding between Fe and O impedes phonon propagation through the oxygen atoms, resulting in lower lattice thermal conductivity. Our work provides a fundamental reference for understanding thermal transport in two-dimensional MOF.

Two-dimensional (2D) rare-earth-based square lattice (SL) quantum magnets provide a pathway to achieve distinctive ground states characterized by unusual excitations. We investigate the magnetic, heat capacity, structural, and electronic properties of a magnetic system Bi₂ErO₄Cl. This compound features a structurally ideal 2D SL composed of Er³⁺rare-earth magnetic ions. The single-phase polycrystalline sample was synthesized using hydrothermal, followed by a vacuum-sealed tube technique. The analysis of heat capacity and magnetic data indicates that the Er³⁺ion adopts aJeff=12state at low temperatures. Fitting the Curie-Weiss (CW) law to the low-temperature magnetic susceptibility data reveals a CW temperature of approximately -2.1 K, suggesting antiferromagnetic (AFM) interactions between the Er³⁺moments. Our first-principles calculations validate a 2D spin model relevant to the titled Er compound. The presence of AFM interaction between the Er³⁺ions is further confirmed using total energy calculations (DFT+U), aligning with the experimental results. The heat capacity measurements reveal the presence of magnetic long-range order belowT_N= 0.47 K. The magnetic heat capacity data followsT^1.8power law dependence belowT_N.

This elementary review article is aimed to the beginning graduate students interested to know basic aspects of Kitaev model. We begin with a very lucid introduction of Kitaev model and present its exact solution, Hilbert space structure, fractionalization, spin-spin correlation function and topological degeneracy in an elementary way. We then discuss the recent proposal of realizing Kitaev interaction in certain materials. Finally we present some recent experiments done on these materials, mainly magnetization, susceptibility, specific heat and thermal Hall effect to elucidate the recent status of material realization of coveted Kitaev spin-liquid phase. We end with a brief discussion on other theoretical works on Kitaev model from different many-body aspects.

Single-layer Bismuth Monobromide (SL-Bi₄Br₄) is a recently experimentally confirmed room temperature quantum spin hall insulator with a relatively large bulk band gap. In this paper, we investigate the electronic properties of SL-Bi₄Br₄and single-layer bismuth monobromide nanoribbon (SL-Bi₄Br₄NR) introducing different vacancy defects near the nanoribbon edges. With maximally localized wannier function (MLWF) constructed Hamiltonian we show that SL-Bi₄Br₄NR edge states are protected by bulk topology and robust against disorder. In conjunction with MLWF and non-equilibrium Green's function, we also show that in devices made from SL-Bi₄Br₄, transmission through the topologically protected edge states do not suffer from degradation when the device is sufficiently wide. Increasing channel length and defect concentration affect only the bulk states transmission leaving edge states transmission perfectly quantized. This resilience against disorder signifies SL-Bi₄Br₄'s promising candidacy for next-generation electronic & spintronics devices application.

We examine a skyrmionium driven over a periodic anisotropy pattern, which consists of disorder free regions and disordered regions. For small defect densities, the skyrmionium flows for an extended range of currents, and there is a critical current above which it transforms into a skyrmion. For increased amounts of quenched disorder, the current needed for the skyrmionium to transform into a skyrmion decreases, and there is a critical disorder density above which a moving skyrmionium is not stable. In the moving state, the skyrmionium to skyrmion transformation leads to a drop in the velocity and the onset of a finite skyrmion Hall angle. We also find a reentrance effect in which the pinned skyrmionium transforms into a skyrmion just above depinning, restabilizes into skyrmionium at larger drives, and becomes unstable again at large currents. We also show that adding a transverse shaking drive can increase the lifetime of a moving skyrmionium by reducing the effect of the pinning in the direction of the drive.

Recently, the chiral induced spin selectivity (CISS) has been demonstrated in different systems such as DNA, proteins, bacteriorhodopsin, helicene and other chiral molecules. In this phenomenon, the spin of the carriers will couple with the chirality of the system and exhibit special transport properties. The explanation of the mechanisms of CISS is still under debating, but it generally accepted that the chirality-induced spin-orbit coupling and the environment play pivotal roles. In addition, in such systems with strong electron-phonon coupling, the moving electrons and holes would interact with phonons to construct polarons as carriers. Therefore, to understand CISS it is needed to focus on the spin-related transport of the polarons. In this paper, we investigate the spin-charge property of a carrier in a chiral helix molecule described with an all-quantum model. Both the extended electron and bound states are obtained analytically. Our findings indicate that the spin and momentum of these carriers are locked, with the nature of this coupling being dictated by the chirality of the system. This work provides valuable insights for theoretical investigations into nonlinear equations and contributes to a deeper understanding of chiral carriers in the context of the CISS effect. Our solution is instructive for theoretical investigation on nonlinear excitations and our results shed new light on the chiral carriers to understand CISS effect.