The modification of electronic band structures and the subsequent tuning of electrical, optical, and thermal material properties is a central theme in the engineering and fundamental understanding of solid-state systems. In this scenario, atomically thin materials offer an appealing platform because they are extremely susceptible to electric and magnetic gating, as well as to interlayer hybridization in stacked configurations, providing the means to customize and actively modulate their response functions. Here, we introduce a radically different approach to material engineering relying on the self-interaction that electrons in a two-dimensional material experience when an electrically neutral structure is placed in its vicinity. Employing rigorous theoretical methods, we show that electrons in a semiconductor atomic monolayer acquire a quantum phase resulting from the image potential induced by the presence of a neighboring periodic array of conducting ribbons, which in turn produces strong modifications in the optical, electrical, and thermal properties of the monolayer, specifically giving rise to the emergence of interband optical absorption, plasmon hybridization, and metal-insulator transitions. Beyond its fundamental interest, material engineering based on the quantum phase induced by noncontact neighboring structures represents a disruptive approach to tailor the properties of atomic layers for application in nanodevices.
Twisted two-dimensional (2D) layered materials exhibit many novel and unique phenomena, such as insulation and superconductivity transition, and superlubricity. However, the effect of twisting on these phenomena remains unclear. A key challenge is the lack of linkage between the twisting and the material properties. Here, twisting induced moiré pattern is directly correlated with the configuration entropy of the bilayer graphene, based on which a new twisting phase transition in layered materials is uncovered. Most critically, the twisting phase transition is found size dependent. The diversit…
In this article, we provide an overview of the basic concepts of novel topological materials. This new class of materials developed by combining the Weyl/Dirac fermionic electron states and magnetism, provide a materials-science platform to test predictions of the laws of topological physics. Owing to their dissipationless transport, these materials hold high promises for technological applications in quantum computing and spintronics devices.
We use a generative neural network model to create thousands of new, one-dimensional materials. The model is trained using 508 stable one-dimensional materials from the Computational 1D Materials Database (C1DB) database. More than 500 of the new materials are shown with density functional theory calculations to be dynamically stable and with heats of formation within 0.2 eV of the convex hull of known materials. Some of the new materials could also have been obtained by chemical element substitution in the training materials, but completely new classes of materials are also produced. The band…
The advent of graphene and other two-dimensional van der Waals materials, with their unique electrical, optical, and thermal properties, has resulted in tremendous progress for fundamental science. Recent developments suggest that taking one more step down in dimensionality - from monolayer, atomic sheets to individual atomic chains - can bring exciting prospects as the ultimate limit in material downscaling is reached while establishing an entirely new field of one-dimensional quantum materials. Here we review this emerging area of one-dimensional van der Waals quantum materials and anticipat…
In this work, we construct a generalized Kane model with a new coupling term between itinerant electron spins and local magnetic moments of anti-ferromagnetic ordering in order to describe the low energy effective physics in a large family of anti-ferromagnetic half-Heusler materials. Topological properties of this generalized Kane model is studied and a large variety of topological phases, including Dirac semimetal phase, Weyl semimetal phase, nodal line semimetal phase, type-B triple point semimetal phase, topological mirror (or glide) insulating phase and anti-ferromagnetic topological insu…
The emergence of graphene and two-dimensional van der Walls materials renewed interest to investigation of the low-frequency noise in the low-dimensional systems. The layered van der Waals materials offers unique opportunities for studying the low-frequency noise owing to the properties controlled by the thickness of these materials, and tunable carrier concentration. In this review, we describe unusual low-frequency noise phenomena in quasi-2D and quasi-1D van der Waals materials. We also demonstrate that the low-frequency noise spectroscopy is a powerful tool for investigation of the electro…
Using the tight-binding approach, we analyze the effect of a one-dimensional superlattice (1DSL) potential on the electronic structure of black phosphorene and transition metal dichalcogenides. We observe that the 1DSL potential results in a decrease of the energy band gap of the two-dimensional (2D) materials. An analytical model is presented to relate the decrease in the direct-band gap to the different orbital characters between the valence band top and conduction band bottom of the 2D materials. The direct-to-indirect gap transition, which occurs under a 1DSL potential with an unequal barr…
Topological phases with insulating bulk and gapless surface or edge modes have attracted much attention because of their fundamental physics implications and potential applications in dissipationless electronics and spintronics. In this review, we mainly focus on the recent progress in the engineering of topologically nontrivial phases (such as $\mathbb{Z}_2$ topological insulators, quantum anomalous Hall effects, quantum valley Hall effects \textit{etc.}) in two-dimensional material systems, including quantum wells, atomic crystal layers of elements from group III to group VII, and the transi…
$Z_{2}$ and Chern topological phases such as newly discovered quantum spin Hall and original quantum Hall states hardly both co--exist in a single material due to their contradictory requirement on the time--reversal symmetry (TRS). We show that although the TRS is broken in systems with a periodically driving ac-field, an effective TRS can still be defined provided the ac--field is linearly polarized or certain other conditions are satisfied. The controllable TRS provides us with a route to manipulate $Z_{2} $ and Chern topological phases in a single material by tuning the polarization of the…
While preserving many of the unusual features of single-layer graphene, few-layer graphene (FLG) provides a richness and flexibility of electronic structure that render this set of materials of great interest for both fundamental studies and applications. Essential for progress, however, is an understanding of the evolution of the electronic structure of these materials with increasing layer number. In this report, the evolution of the electronic structure of FLG, for N = 1 - 8 atomic layers, has been characterized by measurements of the optical conductivity spectra. For each layer thickness N…
The discovery of graphene and other two-dimensional (2-D) materials has stimulated a general interest in low-dimensional (low-D) materials. Whereas long time ago, Peierls and Landau's theoretical work demonstrated that any one- and two-dimensional materials could not exist in any finite temperature environment. Then, two basic issues became a central concern for many researchers: How can stable low-D materials exist? What kind of low-D materials are stable? Here, we establish an energy stability criterion for low-D materials, which seeks to provide a clear answer to these questions. For a cert…
Two-dimensional materials, such as graphene, boron nitride and transition metal dichalcogenides, have attracted increased interest due to their potential applications in electronics and optoelectronics. Thermal transport in two-dimensional materials could be quite different from three-dimensional bulk materials. This article reviews the progress on experimental measurements and theoretical modeling of phonon transport and thermal conductivity in two-dimensional materials. We focus our review on a few typical two-dimensional materials, including graphene, boron nitride, silicene, transition met…
There has been a huge increase of interests in two-dimensional van der Waals materials over the past ten years or so with the conspicuous absence of one particular class of materials: magnetic van der Waals systems. In this Viewpoint, we point it out and illustrate how we might be able to benefit from exploring these so-far neglected materials.
Large-area single-crystal monolayers of two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) can be grown by chemical vapour deposition (CVD). However, the high temperatures and fast timescales at which the conversion from a gas-phase precursor to the 2D material appear, make it extremely challenging to simultaneously follow the atomic arrangements. We utilise helium atom scattering to discover and control the growth of novel 2D h-BN nanoporous phases during the CVD process. We find that prior to the formation of h-BN from the gas-phase precursor, a metastable $(3…
In this research, atomistic molecular dynamics simulations are combined with mesoscopic phase-field computational methods in order to investigate phase-transformation in polycrystalline Aluminum microstructure. In fact, microstructural computational modeling of engineering materials could help to optimize their mechanical properties for industrial applications (e.g. directional solidification for turbine blades). As a result, a multiscale modeling approach is developed to find a relation between manufacturing variables (e.g. temperature) and microstructural properties of crystalline materials …
One of the holy grails of materials science, unlocking structure-property relationships, has largely been pursued via bottom-up investigations of how the arrangement of atoms and interatomic bonding in a material determine its macroscopic behavior. Here we consider a complementary approach, a top-down study of the organizational structure of networks of materials, based on the interaction between materials themselves. We unravel the complete "phase stability network of all inorganic materials" as a densely-connected complex network of 21,000 thermodynamically stable compounds (nodes) interlink…
In recent years, noncollinear topological textures have long gained increasing research attentions for their high values of both fundamental researches and potential applications. The recent discovery of intrinsic orders in magnetic and polar two-dimensional van der Waals materials provides a new ideal platform for the investigation of noncollinear topological textures. Here, we review the theoretical and experimental progresses on noncollinear topological textures in two-dimensional van der Waals materials in very recent years. During these years, magnetic skyrmions of both Bloch and Néel typ…
The discovery and optimization of phase-change and shape memory alloys remain a tedious and expensive process. Here a simple computational method is proposed to determine the ideal phase-change material for a given alloy composed of three elements. Using first-principles calculations, within a high-throughput framework, the ideal composition of a phase-change material between any two assumed phases can be determined. This ideal composition minimizes the interface strain during the structural transformation. Then one can target this ideal composition experimentally to produce compounds with low…
Two-dimensional (2D) materials, such as graphene and MoS2, have been attracting wide interest in surface enhancement Raman spectroscopy. This perspective gives an overview of recent developments in 2D materials' application in surface enhanced Raman spectroscopy. This review focuses on the applications of using bare 2D materials and metal/2D material hybrid substrate for Raman enhancement. The Raman enhancing mechanism of 2D materials will also be discussed. The progress covered herein shows great promise for widespread adoption of 2D materials in SERS application.
Recent atomic pair distribution function results from our group from manganites and cuprate systems are reviewed in light of the presence of multi-scale structures. These structures have a profound effect on the material properties
The last decade has seen intense research in materials with reduced dimensionality. The low dimensionality leads to interesting electronic behavior due to electronic confinement and reduced screening. The investigations have to a large extent focused on 2D materials both in their bulk form, as individual layers a few atoms thick, and through stacking of 2D layers into heterostructures. The identification of low-dimensional compounds is therefore of key interest. Here, we perform a geometric analysis of material structures, demonstrating a strong clustering of materials depending on their dimen…
Phase-change materials (PCMs) are the subject of considerable interest because they have been recognized as potential active layers for next-generation non-volatile memory devices, known as Phase Change Random Access Memories (PRAMs). By analyzing First Principles Molecular Dynamics simulations we develop a new method for the enumeration of mechanical constraints in the amorphous phase and show that the phase diagram of the most popular system (Ge-Sb-Te) can be split into two compositional regions having a well-defined mechanical character: a Tellurium rich flexible phase, and a stressed rigid…
We propose a novel concept of left-handed metamaterial assembly by semiconductor based low-dimensional quantum structures. We theoretically demonstrate the left-handed material, combined from low-dimensional semiconductor quantum wells or quantum dots. One of the most important advantages of the proposed scheme is the possible controllability of material regime and the ability to invert the material losses to gain by using active, pumped quantum structure.
Nonlinear optical responses are often used as a probe for studying electronic properties of materials. For topological materials, studies so far focused on the photogalvanic electric current, which requires breaking inversion symmetry. In this work we present a theory of orbital current response in inversion-symmetric topological insulators. We find a symmetry-allowed orbital current response that occurs in centrosymmetric materials under illumination by linearly polarized light. The sign of the dc nonlinear conductivity reflects the $\mathbb{Z}_2$ index and the conductivity changes sign at th…
Multi-phase materials are key for modern engineering applications. They are generally characterized by a high strength and ductility. Many of these materials fail by ductile fracture of the, generally softer, matrix phase. In this work we systematically study the influence of the arrangement of the phases by correlating the microstructure of a two-phase material to the onset of ductile failure. A single topological feature is identified in which critical levels of damage are consistently indicated. It consists of a small region of the matrix phase with particles of the hard phase on both sides…
Crystal phase is well studied and presents a periodical atom arrangement in three dimensions lattice, but the "amorphous phase" is poorly understood. Here, by starting from cage-like bicyclocalix[2]arene[2]triazines building block, a brand-new 2D MOF is constructed with extremely weak interlaminar interaction existing between two adjacent 2D-crystal layer. Inter-layer slip happens under external disturbance and leads to the loss of periodicity at one dimension in the crystal lattice, resulting in an interim phase between the crystal and amorphous phase - the chaos phase, non-periodical in micr…
In this work we discuss the measurement protocols for indirect determination of the isothermal entropy change associated with first order phase transitions in caloric materials. The magneto- structural phase transitions giving rise to giant magnetocaloric effects in Cu-doped MnAs and FeRh are used as case studies to exemplify how badly designed protocols may affect isothermal measure- ments and lead to incorrect entropy change estimations. Isothermal measurement protocols which allow correct assessment of the entropy change around first order phase transitions in both direct and inverse cases …
We investigate three-dimensional left-handed and related meta-materials based on a fully symmetric multi-gap single-ring SRR design and crossing continuous wires. We demonstrate isotropic transmission properties of a SRR-only meta-material and the corresponding left-handed material which possesses a negative effective index of refraction due to simultaneously negative effective permeability and permittivity. Minor deviations from complete isotropy are due to the finite thickness of the meta-material.
We discover presence of chemical inductive effects in phase separating ion intercalation energy storage materials, specifically in lithium iron phosphate (LFP) and also lithium titanate oxide (LTO). These materials features fast (de)intercalation and slow diffusion relaxation phenomena which are prerequisites for observing such inductive effects. Presented finding is supported by the mechanistic model and analytical reasoning indicating that all equilibrium states that lay inside the miscibility gap of the phase separating material exhibit strong inductive response in the low frequency part of…
Understanding the microstructural influence on the failure mechanisms in multi-phase materials calls for the identification of the worst-case scenario. This necessitates a statistical approach. By performing simulations directly based on micrographs, such an approach becomes feasible. This is applied here to extract the average microstructure around damage sites.
The precise mechanisms underlying the failure of multi-phase materials may be strongly dependent on the material's microstructural morphology. Micromechanical modeling has provided much insight into this dependence, but uncertainties remain about crucial modeling assumptions. This paper assesses the influence of different grain shapes, damage indicators, and stress states using a structured numerical model. A distinct spatial arrangement of phases around fracture incidents is found, consisting of hard regions in the tensile direction interrupted by soft regions in the directions of shear. Thes…
Soft-phonon modes of an undistorted phase encode a material's preference for symmetry lowering. However, the evidence is sparse for the relationship between an unstable phonon wavevector's reciprocal and the number of formula units in the stable distorted phase. This "1/q*-criterion" holds great potential for the first-principles design of materials, especially in low-dimension. We validate the approach on the Q1D materials space containing 1199 ring-metal units and identify candidates that are stable in undistorted (1 unit), Peierls (2 units), charge density wave (3-5 units), or long wave (>5…
MaterialsMap: A CALPHAD-Based Tool to Design Composition Pathways through feasibility map for Desired Dissimilar Materials, demonstrated with RSW Joining of Ag-Al-Cu
Heavy plastic shear deformation at relatively low homologous temperatures is called high-pressure torsion (HPT) deformation, which is one method of severe plastic deformation (SPD). The aim of the paper is to give an overview of a new processing approach which permits the generation of innovative metastable materials and novel nanocomposites by HPT deformation. Starting materials can be either coarse-grained multi-phase alloys, a mixture of different elemental powders or any other combination of multiphase solid starting materials. After HPT processing, the achievable microstructures are simil…
Dynamic control of conductivity and optical properties via atomic structure changes is of tremendous technological importance in information storage. Energy consumption considerations provide a driving force toward employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically-thin materials that can exist in multiple crystal structures, each with distinct electrical properties. Using density functional approaches, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transition…
Second harmonic generation in negative index metamaterials is considered. Theoretical analysis of the corresponding model demonstrated significant difference of this phenomenon in conventional and negative index materials. In contrast to conceptional materials there is nonzero critical phase mismatch. The behavior of interacting weaves is dramatically different when phase mismatch is smaller or greater than critical value.
Massive Discovery of Low-Dimensional Materials from Universal Computational Strategy
Nanoscience Center, Department of Physics, University of Jyväskylä（于韦斯屈莱大学）；Department of Physics, Chalmers University of Technology（查尔姆斯理工大学）；Microelectronics Research Unit, Faculty of Information Technology and Electrical Engineering, University of Oulu（奥卢大学）
Fatigue fracture in ductile materials, e. g. metals, is caused by cyclic plasticity. Especially regarding the high numbers of load cycles, plastic material models resolving the full loading path are computationally very demanding. Herein, a model with particularly small computational effort is presented. It provides a macroscopic, phenomenological description of fatigue fracture by combining the phase-field method for brittle fracture with a classic durability concept. A local lifetime variable is obtained, which degrades the fracture resistance progressively. By deriving the stress-strain pat…
We study theoretically the quenching of a charge-density-wave phase in a model system of a quasi-two dimensional material, which includes both electron-hole and electron-phonon interactions leading, respectively to excitonic and coherent-phonon contributions. We discuss how interaction processes affect anomalous expectation values and present a microscopic dynamical picture of the quenching of the phase. We use projection techniques to illustrate the time-dependent appearance of additional bands and anomalous expectation values. We propose an optical amplification effect with a high modulation…
We use extensive first principle simulations to show the major role played by interfaces in the mechanism of phase separation observed in semiconductor multifunctional materials. We make an analogy with the precipitation sequence observed in over-saturated AlCu alloys, and replace the Guinier-Preston zones in this new context. A new class of materials, the $α$ phases, is proposed to understand the formation of the coherent precipitates observed in the GeMn system. The interplay between formation and interface energies is analyzed for these phases and for the structures usually considered in th…
Dimensionality provides a clear fingerprint on the dispersion of infrared-active, polar-optical phonons. For these phonons, the local dipoles parametrized by the Born effective charges drive the LO-TO splitting of bulk materials; this splitting actually breaks down in two-dimensional materials. Here, we extend the existing theory to the one-dimensional (1D) case. Combining an analytical model with the implementation of density-functional perturbation theory in 1D boundary conditions, we show that the dielectric splitting in the dispersion relations collapses logarithmically at the zone center.…
The approximate location in the Zaanen-Sawatzky-Allen diagram of the phase-separated (Ga,Mn)As material, consisting of MnAs nanoclusters embedded in GaAs, is determined on the basis of configuration-interaction (CI) cluster-model analysis of their Mn 2p core-level photoemission. The composite material is found to belong to the special class of materials with negative charge-transfer energy (delta). As such, its metallic or insulating/semiconducting behavior depends on the strength of the p-d hybridization (affected by strain) relative to the (size-dependent) p-bandwidth. Whereas internal strai…
A Boltzmann statistical approach for the analysis of polarization states in mixed phase ferroelectric materials: application to morphological phase boundary
We perform a computational screening for two-dimensional magnetic materials based on experimental bulk compounds present in the Inorganic Crystal Structure Database and Crystallography Open Database. A recently proposed geometric descriptor is used to extract materials that are exfoliable into two-dimensional derivatives and we find 85 ferromagnetic and 61 anti-ferromagnetic materials for which we obtain magnetic exchange and anisotropy parameters using density functional theory. For the easy-axis ferromagnetic insulators we calculate the Curie temperature based on classical Monte Carlo simula…
In this article, we report emergence of topological phase in XMR material TmSb under hydrostatic pressure using first principles calculations. We find that TmSb, a topologically trivial semimetal, undergoes a topological phase transition with band inversion at X point without breaking any symmetry under a hydrostatic pressure of 12 GPa. At 15 GPa, it again becomes topologically trivial with band inversion at $Γ$ as well as X point. We find that the pressures corresponding to the topological phase transitions are far below the pressure corresponding to structural phase transition at 25.5 GPa. T…
The average and local structures of the (PbTe)1-x(PbS)x system of thermoelectric materials has been studied using the Rietveld and atomic pair distribution function (PDF) methods. Samples with 0:25 < x are macroscopically phase separated. Phase separation was suppressed in a quenched x = 0:5 sample which, nonetheless, exhibited a partial spinodal decomposition. The promising thermoelectric material with x = 0:16 showed intermediate behavior. Combining TEM and bulk scattering data suggests that the sample is a mixture of PbTe rich material and a partially spinodally decomposed phase similar to …
The fundamental electrical and thermal properties of the devices consisting of SnxTe1-x/Sb2Te3 superlattice (SnTeSL) materials have been investigated and compared with those of the conventional Ge2Sb2Te5 (GST225) and GeTe/Sb2Te3 superlattice (GeTeSL) in terms of their resistance switching characteristics. A significant reduction in the switching power of SnTeSL is demonstrated by conducting a proper initialization procedure, varying x in SnxTe1-x/Sb2Te3, and applying short electric pulses. It is found that the observed drastic power reduction occurs due to the exponential decrease in the elect…
Two-dimensional (2D) materials enable new types of magnetic and electronic phases mediated by their reduced dimensionality like magic-angle induced phase transitions, 2D Ising antiferromagnets and ferromagnetism in 2D atomic layers and heterostructures. However, only a few methods are available to study these phase transitions, which for example is particularly challenging for antiferromagnetic materials. Here, we demonstrate that these phases can be probed by the mechanical motion: the temperature dependent resonance frequency and quality factor of multilayer 2D material membranes show clear …
Comprehensive review of investigations of substances with a small difference in the energies of the ferroelectric and antiferroelectric types of dipole ordering is presented. Detailed analysis of the stability of homogeneous phases and conditions for existence of the inhomogeneous state of the substance containing domains of the coexisting ferroelectric and antiferroelectric phases is presented. It is shown that the interaction of locally separated domains of the ferroelectric and antiferroelectric phases stabilizes an inhomogeneous state of these materials. The analysis of physical phenomena …
Manganese dioxide nanorods were synthesized using novel solution route. The phase and microstructure of synthesized materials were identified using X ray diffraction, scanning electron and transmission electron microscopic measurements. The material crystallizes into beta crystallographic phase and consists of nanorods of diameter in the range of about 10-14 nm and length about 50 nm. The Fourier Transform Infrared (FTIR) spectroscopic and thermogravimetric analysis (TGA) measurements were carried out to understand the materials microscopic and thermal properties. The material exhibits charact…
The major obstacle in the design of materials with low lattice thermal conductivity is the difficulty in efficiently scattering phonons across the entire frequency spectrum. Using first principles calculations, we show that driving PbTe materials to the brink of the ferroelectric phase transition could be a powerful strategy to solve this problem. We illustrate this concept by applying tensile [001] strain to PbTe and its alloys with another rock-salt IV-VI material, PbSe; and by alloying PbTe with a rhombohedral IV-VI material, GeTe. This induces extremely soft optical modes at the zone cente…
Two-dimensional (2D) materials have been extensively studied in recent years due to their unique properties and great potential for applications. Different types of structural defects could present in 2D materials and have strong influence on their properties. Optical spectroscopic techniques, e.g. Raman and photoluminescence (PL) spectroscopy, have been widely used for defect characterization in 2D materials. In this review, we briefly introduce different types of defects and discuss their effects on the mechanical, electrical, optical, thermal, and magnetic properties of 2D materials. Then, …
A possibility of use of the controlled decomposition of solid solutions of oxides with perovskite structure in the state of coexisting domains of the antiferroelectric (AFE) and ferroelectric (FE) phases for manufacturing of materials with negative refractive index is demonstrated. The lead zirconate titanate based solid solutions are considered as an example of substances suitable for creation of such materials. Manufactured composites constitute a dielectric matrix with a structure of conducting interphase boundaries separating domains of the FE and AFE phases. The electric conductivity of i…
We perform high-throughput first-principles computations to search the high Curie temperature ($T_{\rm C}$) two-dimensional ferromagnetic (2DFM) materials. We identify 79 2DFM materials and calculate their $T_{\rm C}$, in which Co$_2$F$_2$ has the highest $T_{\rm C}$=541K, well above the room temperature. The 79 2DFM materials are classified into different structural prototypes according to their structural similarity. We perform sure independence screening and sparsifying operator (SISSO) analysis to explore the relation between $T_{\rm C}$ and the material structures. The results suggest tha…
