arXiv subjects

Menghao Wu

Publications and source records attributed to Menghao Wu.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry-engineering ferroelectricity in silicon dioxides

It is a long-established rule for classical ferroelectricity that any ferroelectric crystal must adopt one of the 10 specific polar point groups. Here we predict a unique type of ferroelectricity that can be generated in some crystals belonging to nonpolar noncentrosymmetric groups. This principle can be applicable to many systems including silicon dioxides, the most widely used dielectric materials. Most of their crystalline phases do not belong the polar groups, while the nonlinear Si-O-Si configurations lead to multiple identical states. We show first-principles evidence that the crystal symmetry forbidding the formation of polarizations, can be broken by either parallel surfaces in thin-films or applying a uniaxial strain. As a result, the multiple identical states are endowed with polarizations of different directions, and low-barrier ferroelectric switching can be realized via transition between them, which can be room-temperature robust down to the thickness of 1 nm. Our findings may not only enable low-cost and large-scale manufacture of ferroelectrics directly integrated in silicon chips, but also open a new avenue for exploring ferroelectricity in prevalent nonpolar materials.

cond-mat.mtrl-sci↗

arXiv2026

Continuously control of polarization via electrically driven long-distance superlubric sliding

Sliding ferroelectricity widely exists in various van der Waals bilayers or multilayers, which is induced by asymmetric stacking of commensurate interface. The greatly reduced switching barriers via interlayer sliding lead to high speed with low energy cost, while they are still much higher compared with superlubric sliding of incommensurate interfaces. The polarizations of such incommensurate interfaces are not switchable, which is the major obstacle of combing superlubricity and sliding ferroelectricity for ultralow barriers. Here we propose a design of such combination based on previous synthesis of lateral heterojunctions of 2D materials, which can be extensively applicable to various systems including PN junctions. In such long-distance superlubric ferroelectricity, the vertical polarization can be continuously controlled by superlubric sliding of incommensurate interfaces between lateral heterojunction bilayers, where the series of multiple stable states are long-sought for artificial synaptic devices. The unconventionality of our findings does not only include unprecedented barriers down to the magnitude of mu-eV, but also unprecedented long ion displacements distinct from the small deviations in classical paradigm of ferroelectricity. Our predicted superlubric sliding electrically driven by low vertical voltage is also hitherto reported, much more efficient compared with previously reported sliding mechanically driven by tips, resolving a major issue for practical applications.

cond-mat.mes-hall↗

arXiv2026

Transition from conventional ferroelectricity to ion-conduction-like ferroelectricity

The cross-unitcell long displacements in some recent emergent ferroelectrics have actually challenged the classical definition of ferroelectricity, while the relative explorations are still in the early stage and even controversial. In this paper we provide a general model that gives the picture for the evolution and transition from typical ferroelectricity to long displacement ferroelectricity, which is classified into type-I and type-II. In particular, type-I with two switching modes of different barriers may switch between conventional ferroelectricity and ion-conduction-like ferroelectricity depending on various factors including electric field, boundaries, vacancies, temperature, etc.., which is demonstrated by first-principles calculations on {\gamma}-AlOOH and CuInP2S6 as two paradigmatic cases. Intriguingly, their polarizations are nonlocal since the boundaries also determine the switching mode and polarization direction, which can be different for the same given crystal structure. Such type-I can be evolved from conventional ferroelectricity as the migration barrier across unitcell is reduced, and will behave like type-II at elevated temperature as the conventional part becomes paraelectric. These unconventional behaviors can be applicable to various systems, and many previously unclarified phenomena can be well explained.

cond-mat.mtrl-sci↗

arXiv2025

Volcano-Like Ferroic Transitions Deviating from the Model of Landau Theory

We predict the existence of abnormal volcano-like temperature dependence of polarization or magnetization with maxima located at elevated temperature, distinct from classical model based on Landau theory. One case is ferroelectricity with long ion displacements and quantized polarizations that cannot be used for expansion in Landau model, and the switching pathway involves various metastable phases where the polar phase is higher both in energy and entropy compared with non-polar phase. Another case is compensated antiferromagnets with two opposite spin lattices of different spin exchange constants. Such difference can be utilized for a unique type of temperature differentiated multiferroicity, where large magnetizations can be reversed upon ferroelectric switching between two Curie temperature with alternating half of spins in paramagnetic state. We demonstrate these proposals by first-principles calculations on several paradigmatic systems, including magnetic bilayers intercalated by Ag ions or metal molecules.

cond-mat.mtrl-sci↗

arXiv2025

Robust Ferroelectricity in Silicon Dioxide upon Intercalation of Ammonia

The nanoelectronic applications of current ferroelectrics have been greatly impeded by their incompatibility with silicon. In this paper we propose a way to induce ferroelectricity in silicon dioxide (SiO2), which is still the most widely used dielectric material in silicon-based chips. We show first-principles evidence that the intercalation of NH3 molecules into crystalline SiO2 is exothermic, where NH3 molecules form quasi-bonds with SiO2, giving rise to large and robust polarizations. In general, such polarization can be reversed via the reformation of N-Si bondings, which is multiaxial so vertical ferroelectricity may emerge in their thin-films of any facets. When the applied external electric field is large enough, however, the system may exhibit unconventional quantized ferroelectricity of unprecedented magnitude, where NH3 may migrate for multiple lattice constants like mobile ions in ion conductors. Compared with ion conductors with charged mobile ions and ion vacancies that may lead to current leakage, herein the intercalated systems can be denoted as neutral ion conductors where both pristine SiO2 and SiO2 filled with NH3 are insulating. Similar ferroelectricity may exist in various SiO2 crystalline polymorphs, its amorphous phase, and other porous structures intercalated by NH3. Our findings may not only resolve the bottleneck issues for the compatibility of ferroelectrics and silicon, but also develop unconventional mechanisms of ferroelectricity.

cond-mat.mtrl-sci↗

arXiv2025

A Principal Submanifold-based Approach for Clustering and Multiscale RNA Correction

RNA structure determination is essential for understanding its biological functions. However, the reconstruction process often faces challenges, such as atomic clashes, which can lead to inaccurate models. To address these challenges, we introduce the principal submanifold (PSM) approach for analyzing RNA data on a torus. This method provides an accurate, low-dimensional feature representation, overcoming the limitations of previous torus-based methods. By combining PSM with DBSCAN, we propose a novel clustering technique, the principal submanifold-based DBSCAN (PSM-DBSCAN). Our approach achieves superior clustering accuracy and increased robustness to noise. Additionally, we apply this new method for multiscale corrections, effectively resolving RNA backbone clashes at both microscopic and mesoscopic scales. Extensive simulations and comparative studies highlight the enhanced precision and scalability of our method, demonstrating significant improvements over existing approaches. The proposed methodology offers a robust foundation for correcting complex RNA structures and has broad implications for applications in structural biology and bioinformatics.

q-bio.BM↗

arXiv2025

Unprecedented superionicity of ultra-low barrier in A0.5CoO2 (A=Li, Zn)

The ion conductivity of a solid-state ion conductor generally increases exponentially upon reduction in ion migration barrier. For prevalent cathode material LiCoO2, the room-temperature ion conductivity and migration barrier are respectively around 10-4 S/cm and 0.3 eV. In this paper, through first-principles calculations we predict the existence of 1D superionicity as the Li ions in O2 LiCoO2 are transformed to Zn0.5CoO2 or Li0.5CoO2 via cation-exchange reaction or deintercalation. The ion migration barriers (0.01-0.02 eV) even lower than room-temperature ~kBT are reduced by more than an order of magnitude compared with LiCoO2, which are facilitated by facile transition of mobile ions between two coordination configurations. The room-temperature ion conductivity is estimated to be over 50 S/cm, enhanced by 2-3 orders of magnitude compared with current highest reported value. Such unprecedented superionicity may also exist in other similar layered ion conductors, which may render technical advances and exotic effects such as ultrafast ion batteries and quantized ferroelectricity.

cond-mat.mtrl-sci↗

arXiv2025

Ferroelectric control of antiferromagnetism via coordination swapping in A2Mo3O8 (A= Mn, Fe, Co)

Transition metal molybdenum oxides A2Mo3O8 (A= Mn, Fe, Co) are known to be polar magnets where A ions are located in either octahedrally or tetrahedrally coordinated sites. In this paper we predict that their polarizations can be reversed via swapping of two coordinations for A ions, giving rise to robust vertical ferroelectricity. Such unique ferroelectricity via coordination swapping can be used to control the Neel vector in altermagnetic Fe2Mo3O8, while the large non-relativistic spin-splittings can be also altered by ferroelectric switching in Luttinger compensated magnetic Mn2Mo3O8, both in the absence of net magnetization. However, their ultra-thin layers may possess net magnetizations that can be reversed upon ferroelectric switching. Our findings provide a new type of multiferroicity as well as a new avenue in control of antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2025

An Inorganic Liquid Crystalline Dispersion with 2D Ferroelectric Moieties

Electro-optical effect based liquid crystal devices have been extensively used in optical modulation techniques, in which the Kerr coefficient reflects the sensitivity of the liquid crystals and determines the strength of the device operational electric field. The Peterlin-Stuart theory and the O'Konski model jointly indicate that a giant Kerr coefficient could be obtained in a material with both a large geometrical anisotropy and an intrinsic polarization, but such a material is not yet reported. Here we reveal a ferroelectric effect in a monolayer two-dimensional mineral vermiculite. A large geometrical anisotropy factor and a large inherent electric dipole together raise the record value of Kerr coefficient by an order of magnitude, till $3.0\times 10^{-4}$ m V$^{-2}$. This finding enables an ultra-low operational electric field of $10^2$-$10^4$ V m$^{-1}$ and the fabrication of electro-optical devices with an inch-level electrode separation, which is not practical previously. Because of its high ultraviolet stability (decay <1% under ultraviolet exposure of 1000 hours), large-scale, and energy-efficiency, prototypical displayable billboards have been fabricated for outdoor interactive scenes. The work provides new insights for both liquid crystal optics and two-dimensional ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2025

Superlubric sliding ferroelectricity

Sliding ferroelectricity may emerge in many van der Waals bilayers/multilayers and the low switching barriers render ultrafast data writing with low energy cost. We note that such barriers are still much higher compared with structural superlubricity, and in this paper we propose a type of superlubric sliding ferroelectricity in homobilayers separated by a different layer that leads to unprecedented low switching barriers due to incommensurate interfaces. For example, the switching barrier of 3R bilayer MoS2 will be respectively reduced by around 2 or 1 order of magnitudes if they are separated by a graphene or BN monolayer, and the required voltage for switching can be about 1 order of magnitude lower. Such superlubric sliding ferroelectricity widely exists in various similar sandwich trilayer systems where the polarizations stem from symmetry breaking in across-layer stacking configurations, and with ultralow barriers of superlubric sliding, their performances for various applications are greatly enhanced compared with homobilayer sliding ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2024

Ubiquitous van der Waals altermagnetism with sliding/moire ferroelectricity

According to the recent studies on sliding/moire ferroelectricity, most 2D van der Waals nonferroelectric monolayers can become ferroelectric via multilayer stacking. In this paper we propose that similar strategy can be used to induce desirable van der Waals altermagnetism with symmetry-compensated collinear magnetic orders and non-relativistic spin splitting. Our first-principles calculations show the pervasive co-existence of sliding ferroelectricity and altermagnetism in a series of magnetic multilayers with anti-parallel stacking configurations. Upon a twist angle in bilayers, moire ferroelectricity can be combined with altermagnetism, while some untwisted bilayers exhibit pseudo-altermagnetism with zero net magnetizations and non-relativistic spin splittings coupled with sliding ferroelectricity. Our study significantly expands the scope of altermagnetism, and its combination with sliding/moire ferroelectricity brings in new physics as well as promising applications, which should stimulate further experimental efforts.

cond-mat.mtrl-sci↗

arXiv2024

Two-dimensional Topological Ferroelectric Metal with Giant Shift Current

The pursuit for "ferroelectric metal" which combines seemingly incompatible spontaneous electric polarization and metallicity, has been assiduously ongoing but remains elusive. Unlike traditional ferroelectrics with a wide band gap, ferroelectric (FE) metals can naturally incorporate nontrivial band topology near the Fermi level, endowing them with additional exotic properties. Here, we show first-principles evidence that the metallic PtBi2 monolayer is an intrinsic two-dimensional (2D) topological FE metal, characterized by out-of-plane polarization and a moderate switching barrier. Moreover, it exhibits a topologically nontrivial electronic structure with Z2 invariant equal to 1, leading to a significant FE bulk photovoltaic effect. A slight strain can further enhance this effect to a remarkable level, which far surpass that of previously reported 2D/3D FE materials. Our work provides an important step towards realizing intrinsic monolayer topological FE metals and paves a promising way for future nonlinear optical devices.

cond-mat.mtrl-sci↗

arXiv2024

Selective and Quasi-continuous Switching of Ferroelectric Chern Insulator Device for Neuromorphic Computing

Topologically protected edge state transport in quantum materials is dissipationless and features quantized Hall conductance, and shows great potential in highly fault-tolerant computing technologies. However, it remains elusive about how to develop topological edge state-based computing devices. Recently, exploration and understanding of interfacial ferroelectricity in various van der Waals heterostructure material systems have received widespread attention among the community of materials science and condensed matter physics3-11. Such ferroelectric polarization emergent at the vdW interface can coexist with other quantum states and thus provides an unprecedented opportunity to electrically switch the topological edge states of interest, which is of crucial significance to the fault-tolerant electronic device applications based on the topological edge states. Here, we report the selective and quasi-continuous ferroelectric switching of topological Chern insulator devices and demonstrate its promising application in noise-immune neuromorphic computing. We fabricate this ferroelectric Chern insulator device by encapsulating magic-angle twisted bilayer graphene with doubly-aligned h-BN layers, and observe the coexistence of the interfacial ferroelectricity and the topological Chern insulating states. This ferroelectricity exhibits an anisotropic dependence on the in-plane magnetic field. By using a VBG pulse with delicately controlled amplitude, we realize the nonvolatile switching between any pair of Chern insulating states and achieve 1280 distinguishable nonvolatile resistance levels on a single device. Furthermore, we demonstrate deterministic switching between two arbitrary levels among the record-high number of nonvolatile resistance levels.

cond-mat.mes-hall↗

arXiv2023

Ferroelectricity in crystals with non-polar point groups

Ferroelectric crystals must adopt one of the 10 polar point groups according to the Neumann's principle. In this paper we propose that this conclusion is based on perfect bulk crystals without taking the boundaries into account, and we show first-principles evidence that ferroelectric polarizations may also be formed in some non-polar point groups as the edges generally break the crystal symmetry, which may even maintain at macroscale. They can be switchable in some systems with weak van der Waals bondings or covalent-like ionic bondings where long ion displacements with moderate barriers are possible. Such unconventional ferroelectricity violates the Neumann's principle and Abrahams' conditions respectively due to the boundaries and long ion displacements, which may explain some unclarified phenomena reported previously as well as significantly expand the scope of ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2023

Atypical sliding and Moire ferroelectricity in pure multilayer graphene

Most non-ferroelectric two-dimensional materials can be endowed with so-called sliding ferroelectricity via non-equivalent homo-bilayer stacking, which is not applicable to mono-element systems like pure graphene bilayer with inversion symmetry at any sliding vector. Herein we show first-principles evidence that multilayer graphene with N>3 can all be ferroelectric, where the polarizations of polar states stem from the symmetry breaking in stacking configurations of across-layer instead of adjacent-layer, which are electrically switchable via interlayer sliding. The non-polar states can also be electrically driven to polar states via sliding, all nearly degenerate in energy, and more diverse states with distinct polarizations will emerge in more layers. In contrast to the ferroelectric Moire domains with opposite polarization directions in twisted bilayers reported previously, the Moire pattern in some multilayer graphene systems (e.g., twisted monolayer-trilayer graphene) possess nonzero net polarizations with domains of the same direction separated by non-polar regions, which can be electrically reversed upon interlayer sliding. The distinct Moire bands of two polar states should facilitate electrical detection of such sliding Moire ferroelectricity during switching.

cond-mat.mes-hall↗

arXiv2022

Across-Layer Sliding Ferroelectricity in Graphene-Based Heterolayers: Asymmetry of Next Neighbor Interlayer Couplings

Although most two-dimensional (2D) materials are non-ferroelectric with highly symmetric lattices, symmetry breaking may take place in their bilayers upon certain stacking order, giving rise to so-called sliding ferroelectricity where the vertical polarizations can be electrically reversed via interlayer translation. However, it is not supposed to appear in systems like graphene bilayer with centro-symmetry at any stacking configuration, and the origin of the recently reported ferroelectricity in graphene bilayer intercalated between h-BN (Nature 2020, 588, 71) is still unclear. Here we propose a model of across-layer sliding ferroelectricity that arises from the asymmetry of next neighbor interlayer couplings. The vertical polarizations in intercalated centro-symmetric 2D materials like graphene bilayer can be switched via multilayer sliding, and the observed ferroelectric hysteresis can be clarified. Moreover, such ferroelectricity can exist in a series of other heterolayers with quasi-degenerate polar states, like graphene bilayer or trilayer on BN substrate, or even with a molecule layer on surface where each molecule can store 1 bit data independently, resolving the bottleneck issue of sliding ferroelectricity for high-density data storage.

cond-mat.mes-hall↗

arXiv2019

Bulk and Two-dimensional Silver and Copper Monohalides: A Unique Class of Materials with Modest Ionicity/Covalency and Ferroelasticity/Multiferroicity

Silver and copper monohalides can be viewed as a class of compounds in the neutral zone between predominantly covalent and ionic compounds, thereby exhibiting neither strong ionicity nor strong covalency. We show ab initio calculation evidence that silver and copper monohalides entail relatively low transition barriers between the non-polar rock-salt phase and the polar zinc-blende phase, due largely to their unique chemical nature of modest iconicity or covalency. Notably, the low transition barriers endow both monohalides with novel mechanical and electronic properties, i.e., coupled ferroelasticity and ferroelectricity with large polarizations and relatively low switching barriers at ambient conditions. Several halides even possess very similar lattice constants and structures as the prevailing semiconductors such as silicon, thereby enabling epitaxial growth on silicon. Moreover, based on extensive structural search, we find that the most stable two-dimensional (2D) polymorphs of the monolayer halides are close or even greater in energy than their bulk counterparts, a feature not usually seen in the family of rock-salt or zinc-blende semiconductors. The low transition barrier between zinc-blende phase and 2D phase is predicted. Moreover, several 2D monolayer halides also exhibit multiferroicity with coupled ferroelasticity or ferroelectricity, thereby rendering their potential applications as high-density integrated memories for efficient data reading and writing. Their surfaces, covered by halides, also provide oxidation resistance and give low cleave energy from layered structure, suggesting high likelihood of experimental synthesis of these 2D polymorphs.

cond-mat.mtrl-sci↗

arXiv2019

Type-II multiferroic Hf$_{2}$VC$_{2}$F$_{2}$ MXene monolayer with high transition temperature

Achieving multiferroic two-dimensional (2D) materials should enable numerous functionalities in nanoscale devices. Until now, however, predicted 2D multiferroics are very few and with coexisting yet only loosely coupled (type-I) ferroelectricity and magnetism. Here, a type-II multiferroic MXene Hf$_{2}$VC$_{2}$F$_{2}$ monolayer is identified, where ferroelectricity originates directly from its magnetism. The noncollinear Y-type spin order generates a polarization perpendicular to the spin helical plane. Remarkably, the multiferroic transition is estimated to occur above room temperature. Our investigation should open the door to a new branch of 2D materials for pursuit of intrinsically strong magnetoelectricity.

cond-mat.mtrl-sci↗