When developing high performance lithium-ion batteries,high capacity is one of the key indicators.In the last decade,the progress of two-dimensional(2 D) materials has provided new opportunities for boosting the stora...When developing high performance lithium-ion batteries,high capacity is one of the key indicators.In the last decade,the progress of two-dimensional(2 D) materials has provided new opportunities for boosting the storage capacity.Here,based on first-principles calculation method,we predict that MnN monolayer,a recently proposed 2 D nodal-loop halfmetal containing the metallic element Mn,can be used as a super high-capacity lithium-ion batteries anode.Its theoretical capacity is above 1554 mA-h/g,more than four times that of graphite.Meanwhile,it also satisfies other requirements for a good anode material.Specifically,we demonstrate that MnN is mechanically,dynamically,and thermodynamically stable.The configurations before and after lithium adsorption exhibit good electrical conductivity.The study of Li diffusion on its surface reveals a very low diffusion barrier(~ 0.12 eV),indicating excellent rate performance.The calculated average open-circuit voltage of the corresponding half-cell at full charge is also very low(~0.22 V),which facilitates higher operating voltage.In addition,the lattice changes of the material during lithium intercalation are very small(~ 1.2%-~4.8%),which implies good cycling performance.These results suggest that 2 D MnN can be a very promising anode material for lithium-ion batteries.展开更多
Layered magnetic materials,such as MnBi_(2)Te_(4),have drawn much attention owing to their potential for realizing twodimensional(2D)magnetism and possible topological states.Recently,FeBi_(2)Te_(4),which is isostruct...Layered magnetic materials,such as MnBi_(2)Te_(4),have drawn much attention owing to their potential for realizing twodimensional(2D)magnetism and possible topological states.Recently,FeBi_(2)Te_(4),which is isostructural to MnBi_(2)Te_(4),has been synthesized in experiments,but its detailed magnetic ordering and band topology have not been clearly understood yet.Here,based on first-principles calculations,we investigate the magnetic and electronic properties of FeBi_(2)Te_(4)in bulk and 2D forms.We show that different from MnBi_(2)Te_(4),the magnetic ground states of bulk,single-layer,and bilayer FeBi_(2)Te_(4)all favor a 120°noncollinear antiferromagnetic ordering,and they are topologically trivial narrow-gap semiconductors.For the bilayer case,we find that a quantum anomalous Hall effect with a unit Chern number is realized in the ferromagnetic state,which may be achieved in experiment by an external magnetic field or by magnetic proximity coupling.Our work clarifies the physical properties of the new material system of FeBi_(2)Te_(4)and reveals it as a potential platform for studying magnetic frustration down to 2D limit as well as quantum anomalous Hall effect.展开更多
The extremely high structural tolerance of ceria to oxygen vacancies(Ov)has made it a desirable catalytic material for the hydrocarbon oxidation to chemicals and pharmaceuticals and the reduction of gaseous pollutants...The extremely high structural tolerance of ceria to oxygen vacancies(Ov)has made it a desirable catalytic material for the hydrocarbon oxidation to chemicals and pharmaceuticals and the reduction of gaseous pollutants.It is proposed that the formation and diffusion of Ov originate from its outstanding reduction property.However,the formation and diffusion process of Ov over the surface of ceria at the atomic level is still unknown.Herein,the structural and valence evolution of CeO_(2)(111)surfaces in reductive,oxidative and vacuum environments from room temperature up to 700℃was studied with in situ aberration-corrected environmental transmission electron microscopy(ETEM)experiments.Ov is found to form under a high vacuum at elevated temperatures;however,the surface can recover to the initial state through the adsorption of oxygen atoms in an oxygen-contained environment.Furthermore,in hydrogen environment,the step-CeO_(2)(111)surface is not stable at elevated temperatures;thus,the steps tend to be eliminated with increasing temperature.Combined with first-principles density function calculations(DFT),it is proposed that O-terminated surfaces would develop in a hypoxic environment due to the dynamic diffusion of Ov from the outer surface to the subsurface.Furthermore,in a reductive environment,H2 facilitates the formation and diffusion of Ov while Ce-terminated surfaces develope.These results reveal dynamic atomic-scale interplay between the nanoceria surface and gas,thereby providing fundamental insights into the Ov-dependent reaction of nano-CeO_(2) during catalytic processes.展开更多
The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconductin...The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconducting transition metal dichalcogenides.Unlike the corresponding bulk material,our simulations show that monolayer MX_2(M = Mo and W;X = S,Se,and Te) exhibits a negative thermal expansion at low temperatures,induced by the bending modes.The transition from contraction to expansion at higher temperatures is observed.Interestingly,the thermal expansion can be tailored regularly by alteration of the M or X atom.Detailed analysis shows that the positive thermal expansion coefficient is determined mainly by the in-plane stiffness,which can be expressed by a simple relationship.Essentially the regularity of this change can be attributed to the difference in charge transfer between the different elements.These findings should be applicable to other two-dimensional systems.展开更多
The field of two-dimensional topological semimetals,which emerged at the intersection of two-dimensional materials and topological materials,has been rapidly developing in recent years.In this article,we briefly revie...The field of two-dimensional topological semimetals,which emerged at the intersection of two-dimensional materials and topological materials,has been rapidly developing in recent years.In this article,we briefly review the progress in this field.Our focus is on the basic concepts and notions,in order to convey a coherent overview of the field.Some material examples are discussed to illustrate the concepts.We discuss the outstanding problems in the field that need to be addressed in future research.展开更多
The coupling between electric ordering and magnetic ordering in two-dimensional(2D)materials is important for both fundamental research of 2D multiferroics and future development of magnetism-based information storage...The coupling between electric ordering and magnetic ordering in two-dimensional(2D)materials is important for both fundamental research of 2D multiferroics and future development of magnetism-based information storage and operation.Here,we introduce a scheme for realizing a magnetic phase transition through the transition of electric ordering.We take CuMoP_(2)S_(6) monolayer as an example,which is a member of the large 2D transition-metal chalcogen-phosphates family.Based on first-principles calculations,we find that it is a multiferroic with unprecedented characters,namely,it exhibits two different phases:an antiferroelectric-antiferromagnetic phase and a ferroelectric-ferromagnetic phase,in which the electric and magnetic orderings are strongly coupled.Importantly,the electric polarization is out-of-plane,so the magnetism can be readily switched by using the gate electric field.Our finding reveals a series of 2D multiferroics with special magnetoelectric coupling,which hold great promise for experimental realization and practical applications.展开更多
Seeking carbon phases with versatile properties is one of the fundamental goals in physics,chemistry,and materials science.Here,based on the first-principles calculations,a family of three-dimensional(3D)graphene netw...Seeking carbon phases with versatile properties is one of the fundamental goals in physics,chemistry,and materials science.Here,based on the first-principles calculations,a family of three-dimensional(3D)graphene networks with abundant and fabulous electronic properties,including rarely reported dipole-allowed truly direct band gap semiconductors with suitable band gaps(1.07–1.87 eV)as optoelectronic/photovoltaic materials and topological nodal-ring semimetals,are proposed through stitching different graphene layers with acetylenic linkages.Remarkably,the optical absorption coefficients in some of those semiconducting carbon allotropes express possibly the highest performance among all of the semiconducting carbon phases known to date.On the other hand,the topological states in those topological nodal-ring semimetals are protected by the time-reversal and spatial symmetry and present nodal rings and nodal helical loops topological patterns.Those newly revealed carbon phases possess low formation energies and excellent thermodynamic stabilities;thus,they not only host a great potential in the application of optoelectronics,photovoltaics,and quantum topological materials etc.,but also can be utilized as catalysis,molecule sieves or Liion anode materials and so on.Moreover,the approach used here to design novel carbon allotropes may also give more enlightenments to create various carbon phases with different applications.展开更多
We theoretically and computationally show the simplest realization of SOC using two-level cold atoms interacting with only one laser beam.The underlying mechanism is based on the non-adiabatic nature of laser-atom int...We theoretically and computationally show the simplest realization of SOC using two-level cold atoms interacting with only one laser beam.The underlying mechanism is based on the non-adiabatic nature of laser-atom interaction,with the Rabi frequency being not much larger than the kinetic energy of the atom.We use Zitterbewegung oscillation to further illustrate the effects of the synthesized SOC on the quantum dynamics of the two-level cold atoms.We expect our proposal to be of experimental interest in the quantum simulation of SOC-related physics.展开更多
Dirac semimetals(DSMs)are an important class of topological states of matter.Here,focusing on DSMs of band inversion type,we investigate their boundary modes from the effective model perspective.We show that in order ...Dirac semimetals(DSMs)are an important class of topological states of matter.Here,focusing on DSMs of band inversion type,we investigate their boundary modes from the effective model perspective.We show that in order to properly capture the boundary modes,k-cubic terms must be included in the effective model,which would drive an evolution of surface degeneracy manifold from a nodal line to a nodal point.Sizable k-cubic terms are also needed for better exposing the topological hinge modes in the spectrum.Using first-principles calculations,we demonstrate that this feature and the topological hinge modes can be clearly exhibited inβ-CuI.We extend the discussion to magnetic DSMs and show that the time-reversal symmetry breaking can gap out the surface bands and hence is beneficial for the experimental detection of hinge modes.Furthermore,we show that magnetic DSMs serve as a parent state for realizing multiple other higher-order topological phases,including higher-order Weyl-point/nodal-line semimetals and higher-order topological insulators.展开更多
The anomalous spatial shifts at interface scattering, first studied in geometric optics, recently found their counterparts in the electronic context. It was shown that both longitudinal and transverse shifts, analogou...The anomalous spatial shifts at interface scattering, first studied in geometric optics, recently found their counterparts in the electronic context. It was shown that both longitudinal and transverse shifts, analogous to the Goos-Hanchen and Imbert-Fedorov effects in optics, can exist when electrons are scattered at a junction interface. More interestingly, the shifts are also discovered in the process of Andreev reflection at a normal/superconductor interface. Particularly, for the case with unconventional superconductors, it was discovered that the transverse shift can arise solely from the superconducting pair potential and exhibit characteristic features depending on the pairing. Here, we briefly review the recent works in this field, with an emphasis on the physical picture and theoretical understanding.展开更多
Recently, emerging phonon phenomena have been discovered and rapidly developed, which have become an active hot research topic. In this review article, we present state-of-the-art advances in several fascinating phono...Recently, emerging phonon phenomena have been discovered and rapidly developed, which have become an active hot research topic. In this review article, we present state-of-the-art advances in several fascinating phonon transport phenomena. First, we summarize the recent progress on the wave nature of phonons, including phonon coherence and its effects on thermal conductivity and the topological properties of phonons. Then, we discuss the particle nature of phonons, including the weak coupling of phonons and the high-order phonon anharmonicity. Finally, we present the summary and a brief outlook. This review presents the advanced understanding of some emerging phonon phenomena in solid materials, which provides new opportunities for further advancement in a wide variety of applications.展开更多
The adsorption effects of 3d transitional metal(TM) adatoms on electronic and magnetic properties of monolayer and bilayer Mo S2 sheets have been investigated by using first-principle calculations based on the density...The adsorption effects of 3d transitional metal(TM) adatoms on electronic and magnetic properties of monolayer and bilayer Mo S2 sheets have been investigated by using first-principle calculations based on the density functional theory. The calculated results suggest that both monolayer and bilayer Mo S2 sheets have power abilities of absorbing 3d TM atoms. The interlayer adsorption of bilayer Mo S2 is relatively more stable than the surface adsorption of monolayer Mo S2. The 3d TM adatoms and the neighboring S atoms behave a clear covalent-binding character. It was found that TM adatoms induce certain impurity states within the band gap of the pristine Mo S2 sheet which result in the systems magnetically semiconducting or half metallic. The adsorbed systems for Cr and Co on the surface of monolayer Mo S2 sheet, as well as Sc, Cr and Fe in the interlayer of bilayer Mo S2 sheet exhibit half-metallic behavior. And the other 3d TMadsorbed systems are magnetic semiconductor except for Ni species.展开更多
Topological metals(TMs)are a kind of special metallic materials,which feature nontrivial band Cross-ings near the Fermi energy,giving rise to peculiar quasiparticle excitations.TMs can be classified based on the chara...Topological metals(TMs)are a kind of special metallic materials,which feature nontrivial band Cross-ings near the Fermi energy,giving rise to peculiar quasiparticle excitations.TMs can be classified based on the characteristics of these band crossings.For example,according to the dimensionality of the crossing,TMs can be classifed into nodal-point,nodal-line,and nodal-surface metals.Another important property is the type of dispersion.According to degree of the tilt of the local dispersion around the crossing,we have typeI and type-II dispersions.This leads to significant distinctions in the physical properties of the materials,owing to their contrasting Fermi surface topologies.In this article,we briefly review the recent advances in this research direction,focusing on the concepts,the physical properties,and the material realizations of the type-Il nodal-point and nodal-line TMs.展开更多
Recently,the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties.Here,we present a systematic study on 1T′-MoTe2 ...Recently,the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties.Here,we present a systematic study on 1T′-MoTe2 single-crystal and exfoliated thin-flakes by means of electrical transport,scanning tunnelling microscope(STM)measurements and band structure calculations.For a bulk sample,it exhibits large magneto-resistance(MR)and Shubnikov–de Hass oscillations inρxx and a series of Hall plateaus inρxy at low temperatures.Meanwhile,the MoTe2 thin films were intensively investigated with thickness dependence.For samples,without encapsulation,an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness.In such thin films,we also observed a suppression of the MR and weak anti-localization(WAL)effects.We attributed these effects to disorders originated from the extrinsic surface chemical reaction,which is consistent with the density functional theory(DFT)calculations and in-situ STM results.In contrast to samples without encapsulated protection,we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride(h-BN)film protection.Our results indicate that the metallic or superconducting behavior is its intrinsic state,and the insulating behavior is likely caused by surface oxidation in few layer 1T’-MoTe2 flakes.展开更多
Emergent Dirac fermion states underlie many intriguing properties of graphene,and the search for them constitutes one strong motivation to explore two-dimensional(2D)allotropes of other elements.Phosphorene,the ultrat...Emergent Dirac fermion states underlie many intriguing properties of graphene,and the search for them constitutes one strong motivation to explore two-dimensional(2D)allotropes of other elements.Phosphorene,the ultrathin layers of black phosphorous,has been a subject of intense investigations recently,and it was found that other group-Va elements could also form 2D layers with similar puckered lattice structure.Here,by a close examination of their electronic band structure evolution,we discover two types of Dirac fermion states emerging in the low-energy spectrum.One pair of(type-I)Dirac points is sitting on high-symmetry lines,while two pairs of(type-II)Dirac points are located at generic k-points,with different anisotropic dispersions determined by the reduced symmetries at their locations.Such fully-unpinned(type-II)2D Dirac points are discovered for the first time.In the absence of spin-orbit coupling(SOC),we find that each Dirac node is protected by the sublattice symmetry from gap opening,which is in turn ensured by any one of three point group symmetries.The SOC generally gaps the Dirac nodes,and for the type-I case,this drives the system into a quantum spin Hall insulator phase.We suggest possible ways to realise the unpinned Dirac points in strained phosphorene.展开更多
Two-dimensional (2D) multiferroics have attracted increasing interests in basic science and technological fields in recent years.However,most reported 2D magnetic ferroelectrics are based on the d-electron magnetism,w...Two-dimensional (2D) multiferroics have attracted increasing interests in basic science and technological fields in recent years.However,most reported 2D magnetic ferroelectrics are based on the d-electron magnetism,which makes them rather rare due to the empirical d^(0) rule and limits their applications for low magnetic phase transition temperature.In this work,we demonstrate that the ferroelectricity can coexist with the p-electron-induced ferromagnetism without the limitation of d^(0) rule and metallicity in a family of stable 2D MXene-analogous oxynitrides,X_(2)NO_(2) (X = In,Tl).Remarkably,the itinerant character of p electrons can lead to the strong ferromagnetic metallic states.Furthermore,a possible magnetoelectric effect is manifested in a Tl_(2)NO_(2)/WTe_(2) heterostructure through the interface engineering.Our findings provide an alternative possible route toward 2D multiferroics and enrich the concept of ferroelectric metals.展开更多
基金Project supported by the Scientific Research Fund of Jiangxi Provincial Education Department,China(Grant No.GJJ190962)the National Natural Science Foundation of China(Grant Nos.11904153,51962010,61961027,12064026,and 12064014)Jiangxi Province Natural Science Foundation,China(Grant No.20202BABL211008)。
文摘When developing high performance lithium-ion batteries,high capacity is one of the key indicators.In the last decade,the progress of two-dimensional(2 D) materials has provided new opportunities for boosting the storage capacity.Here,based on first-principles calculation method,we predict that MnN monolayer,a recently proposed 2 D nodal-loop halfmetal containing the metallic element Mn,can be used as a super high-capacity lithium-ion batteries anode.Its theoretical capacity is above 1554 mA-h/g,more than four times that of graphite.Meanwhile,it also satisfies other requirements for a good anode material.Specifically,we demonstrate that MnN is mechanically,dynamically,and thermodynamically stable.The configurations before and after lithium adsorption exhibit good electrical conductivity.The study of Li diffusion on its surface reveals a very low diffusion barrier(~ 0.12 eV),indicating excellent rate performance.The calculated average open-circuit voltage of the corresponding half-cell at full charge is also very low(~0.22 V),which facilitates higher operating voltage.In addition,the lattice changes of the material during lithium intercalation are very small(~ 1.2%-~4.8%),which implies good cycling performance.These results suggest that 2 D MnN can be a very promising anode material for lithium-ion batteries.
基金Supported by the National Basic Research Program of China under Grant No 2012CB921300, and the National Natural Science Foundation of China under Grant Nos 11274280 and 11104254.
基金funding support from the Singapore MOE Ac RF 308 Tier 2(Grant No.T2EP50220-0026)funding support from Shandong Provincial Natural Science Foundation(Grant No.ZR2023QA012)+3 种基金the Special Fund-ing in the Project of Qilu Young Scholar Program of Shandong Universityfunding support from Australian Research Council Future Fellowship(Grant No.FT220100290)funding support from the AINSE postgraduate awardfunding support from the Research and Development Administration Office at the University of Macao(Grants Nos.MYRG2022-00088-IAPME and SRG2021-00003-IAPME)。
文摘Layered magnetic materials,such as MnBi_(2)Te_(4),have drawn much attention owing to their potential for realizing twodimensional(2D)magnetism and possible topological states.Recently,FeBi_(2)Te_(4),which is isostructural to MnBi_(2)Te_(4),has been synthesized in experiments,but its detailed magnetic ordering and band topology have not been clearly understood yet.Here,based on first-principles calculations,we investigate the magnetic and electronic properties of FeBi_(2)Te_(4)in bulk and 2D forms.We show that different from MnBi_(2)Te_(4),the magnetic ground states of bulk,single-layer,and bilayer FeBi_(2)Te_(4)all favor a 120°noncollinear antiferromagnetic ordering,and they are topologically trivial narrow-gap semiconductors.For the bilayer case,we find that a quantum anomalous Hall effect with a unit Chern number is realized in the ferromagnetic state,which may be achieved in experiment by an external magnetic field or by magnetic proximity coupling.Our work clarifies the physical properties of the new material system of FeBi_(2)Te_(4)and reveals it as a potential platform for studying magnetic frustration down to 2D limit as well as quantum anomalous Hall effect.
基金Project supported by the National Key Research and Development Plan(2021YFA1200201)the Natural Science Foundation of China(51872008)+1 种基金the"111"Project under the DB18015 grantBeijing Outstanding Young Scientists Projects(BJJWZYJH01201910005018)。
文摘The extremely high structural tolerance of ceria to oxygen vacancies(Ov)has made it a desirable catalytic material for the hydrocarbon oxidation to chemicals and pharmaceuticals and the reduction of gaseous pollutants.It is proposed that the formation and diffusion of Ov originate from its outstanding reduction property.However,the formation and diffusion process of Ov over the surface of ceria at the atomic level is still unknown.Herein,the structural and valence evolution of CeO_(2)(111)surfaces in reductive,oxidative and vacuum environments from room temperature up to 700℃was studied with in situ aberration-corrected environmental transmission electron microscopy(ETEM)experiments.Ov is found to form under a high vacuum at elevated temperatures;however,the surface can recover to the initial state through the adsorption of oxygen atoms in an oxygen-contained environment.Furthermore,in hydrogen environment,the step-CeO_(2)(111)surface is not stable at elevated temperatures;thus,the steps tend to be eliminated with increasing temperature.Combined with first-principles density function calculations(DFT),it is proposed that O-terminated surfaces would develop in a hypoxic environment due to the dynamic diffusion of Ov from the outer surface to the subsurface.Furthermore,in a reductive environment,H2 facilitates the formation and diffusion of Ov while Ce-terminated surfaces develope.These results reveal dynamic atomic-scale interplay between the nanoceria surface and gas,thereby providing fundamental insights into the Ov-dependent reaction of nano-CeO_(2) during catalytic processes.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274280 and 11104254)the National Basic Research Program of China(Grant No.2012CB921300)
文摘The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconducting transition metal dichalcogenides.Unlike the corresponding bulk material,our simulations show that monolayer MX_2(M = Mo and W;X = S,Se,and Te) exhibits a negative thermal expansion at low temperatures,induced by the bending modes.The transition from contraction to expansion at higher temperatures is observed.Interestingly,the thermal expansion can be tailored regularly by alteration of the M or X atom.Detailed analysis shows that the positive thermal expansion coefficient is determined mainly by the in-plane stiffness,which can be expressed by a simple relationship.Essentially the regularity of this change can be attributed to the difference in charge transfer between the different elements.These findings should be applicable to other two-dimensional systems.
基金supported by the Singapore Ministry of Education AcRF Tier 2(Grant No.MOE2019-T2-1-101).
文摘The field of two-dimensional topological semimetals,which emerged at the intersection of two-dimensional materials and topological materials,has been rapidly developing in recent years.In this article,we briefly review the progress in this field.Our focus is on the basic concepts and notions,in order to convey a coherent overview of the field.Some material examples are discussed to illustrate the concepts.We discuss the outstanding problems in the field that need to be addressed in future research.
基金Supported by the National Key R&D Program of China(Grant No.2019YFE0112000)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LR21A040001)the National Natural Science Foundation of China(Grant No.11974307,12088101,11991060,and U1930402).
文摘The coupling between electric ordering and magnetic ordering in two-dimensional(2D)materials is important for both fundamental research of 2D multiferroics and future development of magnetism-based information storage and operation.Here,we introduce a scheme for realizing a magnetic phase transition through the transition of electric ordering.We take CuMoP_(2)S_(6) monolayer as an example,which is a member of the large 2D transition-metal chalcogen-phosphates family.Based on first-principles calculations,we find that it is a multiferroic with unprecedented characters,namely,it exhibits two different phases:an antiferroelectric-antiferromagnetic phase and a ferroelectric-ferromagnetic phase,in which the electric and magnetic orderings are strongly coupled.Importantly,the electric polarization is out-of-plane,so the magnetism can be readily switched by using the gate electric field.Our finding reveals a series of 2D multiferroics with special magnetoelectric coupling,which hold great promise for experimental realization and practical applications.
基金We wish to thank Peng-Jie Guo,Zhongwei Zhang,and Weikang Wu for helpful discussions.This work was supported by the National Key R&D Program of China(Grants no.2019YFA0308603 and 2017YFA0302903)the National Natural Science Foundation of China(Grants no.11934020,11774424,and 11804039)+1 种基金the Singapore Ministry of Education AcRF Tier 2(MOE2017-T2-2-108)Y.G.was supported by the Outstanding Innovative Talents Cultivation Funded Programs 2021 of Renmin University of China.Computational resources were provided by the Physical Laboratory of High-Performance Computing at the Renmin University of China.
文摘Seeking carbon phases with versatile properties is one of the fundamental goals in physics,chemistry,and materials science.Here,based on the first-principles calculations,a family of three-dimensional(3D)graphene networks with abundant and fabulous electronic properties,including rarely reported dipole-allowed truly direct band gap semiconductors with suitable band gaps(1.07–1.87 eV)as optoelectronic/photovoltaic materials and topological nodal-ring semimetals,are proposed through stitching different graphene layers with acetylenic linkages.Remarkably,the optical absorption coefficients in some of those semiconducting carbon allotropes express possibly the highest performance among all of the semiconducting carbon phases known to date.On the other hand,the topological states in those topological nodal-ring semimetals are protected by the time-reversal and spatial symmetry and present nodal rings and nodal helical loops topological patterns.Those newly revealed carbon phases possess low formation energies and excellent thermodynamic stabilities;thus,they not only host a great potential in the application of optoelectronics,photovoltaics,and quantum topological materials etc.,but also can be utilized as catalysis,molecule sieves or Liion anode materials and so on.Moreover,the approach used here to design novel carbon allotropes may also give more enlightenments to create various carbon phases with different applications.
基金Supported by the National Research Foundation and Ministry of Education,Singapore under Grant No WBS:R-710-000-008-271by the National Natural Science Foundation of China under Grant No 11105123.
文摘We theoretically and computationally show the simplest realization of SOC using two-level cold atoms interacting with only one laser beam.The underlying mechanism is based on the non-adiabatic nature of laser-atom interaction,with the Rabi frequency being not much larger than the kinetic energy of the atom.We use Zitterbewegung oscillation to further illustrate the effects of the synthesized SOC on the quantum dynamics of the two-level cold atoms.We expect our proposal to be of experimental interest in the quantum simulation of SOC-related physics.
文摘Dirac semimetals(DSMs)are an important class of topological states of matter.Here,focusing on DSMs of band inversion type,we investigate their boundary modes from the effective model perspective.We show that in order to properly capture the boundary modes,k-cubic terms must be included in the effective model,which would drive an evolution of surface degeneracy manifold from a nodal line to a nodal point.Sizable k-cubic terms are also needed for better exposing the topological hinge modes in the spectrum.Using first-principles calculations,we demonstrate that this feature and the topological hinge modes can be clearly exhibited inβ-CuI.We extend the discussion to magnetic DSMs and show that the time-reversal symmetry breaking can gap out the surface bands and hence is beneficial for the experimental detection of hinge modes.Furthermore,we show that magnetic DSMs serve as a parent state for realizing multiple other higher-order topological phases,including higher-order Weyl-point/nodal-line semimetals and higher-order topological insulators.
文摘The anomalous spatial shifts at interface scattering, first studied in geometric optics, recently found their counterparts in the electronic context. It was shown that both longitudinal and transverse shifts, analogous to the Goos-Hanchen and Imbert-Fedorov effects in optics, can exist when electrons are scattered at a junction interface. More interestingly, the shifts are also discovered in the process of Andreev reflection at a normal/superconductor interface. Particularly, for the case with unconventional superconductors, it was discovered that the transverse shift can arise solely from the superconducting pair potential and exhibit characteristic features depending on the pairing. Here, we briefly review the recent works in this field, with an emphasis on the physical picture and theoretical understanding.
基金supported by the National Natural Science Foundation of China(11974307,61574123,11674299,and 11634011)National Key Research and Development Program of China(2017YFA0204904)+3 种基金Fundamental Research Funds for the Central Universities(2019FZA3004,WK2340000082,and WK2060190084)Zhejiang Provincial Natural Science Foundation(D19A040001)Anhui Initiative in Quantum Information Technologies(AHY170000)Strategic Priority Research Program of Chinese Academy of Sciences(XDB30000000)。
基金supported by the National Key R&D Program of China(2020YFA0308800,2016YFA0300600,and 2017YFB0701600)the National Natural Science Foundation of China(11734003,12061131002,12004028,and 12004035)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB30000000)the China Postdoctoral Science Foundation(2020M670106)the Singapore Ministry of Education AcRF Tier 2(MOE2019-T2-1-001)Beijing Institute of Technology Research Fund Program for Young Schola。
基金supported in part by the National Natural Science Foundation of China (Grant Nos. 11890703, and 12075168)the Science and Technology Commission of Shanghai Municipality (Grant Nos. 19ZR1478600, and 21JC1405600)+3 种基金the Fundamental Research Funds for the Central Universities (Grant No. 22120220060)supported in part by the RIE2020 Advanced Manufacturing and Engineering (AME) Programmatic (Grant No. A1898b0043)Singapore Aerospace Programme Cycle 15 (Grant No. M2115a0092)supported by the Singapore Ministry of Education AcRF Tier 2 (Grant No. T2EP50220-0026)。
文摘Recently, emerging phonon phenomena have been discovered and rapidly developed, which have become an active hot research topic. In this review article, we present state-of-the-art advances in several fascinating phonon transport phenomena. First, we summarize the recent progress on the wave nature of phonons, including phonon coherence and its effects on thermal conductivity and the topological properties of phonons. Then, we discuss the particle nature of phonons, including the weak coupling of phonons and the high-order phonon anharmonicity. Finally, we present the summary and a brief outlook. This review presents the advanced understanding of some emerging phonon phenomena in solid materials, which provides new opportunities for further advancement in a wide variety of applications.
基金financially supported by the National Basic Research Program of China (No. 2012CB921300)
文摘The adsorption effects of 3d transitional metal(TM) adatoms on electronic and magnetic properties of monolayer and bilayer Mo S2 sheets have been investigated by using first-principle calculations based on the density functional theory. The calculated results suggest that both monolayer and bilayer Mo S2 sheets have power abilities of absorbing 3d TM atoms. The interlayer adsorption of bilayer Mo S2 is relatively more stable than the surface adsorption of monolayer Mo S2. The 3d TM adatoms and the neighboring S atoms behave a clear covalent-binding character. It was found that TM adatoms induce certain impurity states within the band gap of the pristine Mo S2 sheet which result in the systems magnetically semiconducting or half metallic. The adsorbed systems for Cr and Co on the surface of monolayer Mo S2 sheet, as well as Sc, Cr and Fe in the interlayer of bilayer Mo S2 sheet exhibit half-metallic behavior. And the other 3d TMadsorbed systems are magnetic semiconductor except for Ni species.
基金The authors thank D.L.Deng for valuable discussions.The work was supported by the National Natural Sei-ence Foundation of China(Grants No.11734003)the National Key R&D Program of China(Grant No.2016YFA0300600)+1 种基金the Strategic P rorty Researei Prugram uf Chimese Aeadeny uf seenes(GraIL No.XD3000000)the Singapore Ministry of Education AcRF Tier 2(Grant Nos.MOE2017-T2-2-108 and MOE2019-T2-1-001).
文摘Topological metals(TMs)are a kind of special metallic materials,which feature nontrivial band Cross-ings near the Fermi energy,giving rise to peculiar quasiparticle excitations.TMs can be classified based on the characteristics of these band crossings.For example,according to the dimensionality of the crossing,TMs can be classifed into nodal-point,nodal-line,and nodal-surface metals.Another important property is the type of dispersion.According to degree of the tilt of the local dispersion around the crossing,we have typeI and type-II dispersions.This leads to significant distinctions in the physical properties of the materials,owing to their contrasting Fermi surface topologies.In this article,we briefly review the recent advances in this research direction,focusing on the concepts,the physical properties,and the material realizations of the type-Il nodal-point and nodal-line TMs.
基金The work was supported by the Guangdong Innovative and Entrepreneurial Research Team Program,China(Grant No.2016ZT06D348)the National Natural Science Foundation of China(Grant No.11874193)the Shenzhen Fundamental Subject Research Program,China(Grant No.JCYJ20170817110751776).K.D.W.acknowledges support from the National Natural Science Foundation of China(Grant No.11574128).X.D.acknowledges support from NSF under award DMR-1808491.
文摘Recently,the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties.Here,we present a systematic study on 1T′-MoTe2 single-crystal and exfoliated thin-flakes by means of electrical transport,scanning tunnelling microscope(STM)measurements and band structure calculations.For a bulk sample,it exhibits large magneto-resistance(MR)and Shubnikov–de Hass oscillations inρxx and a series of Hall plateaus inρxy at low temperatures.Meanwhile,the MoTe2 thin films were intensively investigated with thickness dependence.For samples,without encapsulation,an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness.In such thin films,we also observed a suppression of the MR and weak anti-localization(WAL)effects.We attributed these effects to disorders originated from the extrinsic surface chemical reaction,which is consistent with the density functional theory(DFT)calculations and in-situ STM results.In contrast to samples without encapsulated protection,we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride(h-BN)film protection.Our results indicate that the metallic or superconducting behavior is its intrinsic state,and the insulating behavior is likely caused by surface oxidation in few layer 1T’-MoTe2 flakes.
基金supported by NSFC(Grant No.11374009,61574123 and 21373184)the National Key Basic Research Program of China(2012CB825700)+5 种基金SUTD-SRG-EPD2013062Singapore MOE Academic Research Fund Tier 1(SUTD-T1-2015004)A*STAR SERC 122-PSF-0017 and AcRF R-144-000-310-112support by Singapore National Research Foundation under NRF Award No.NRF-NRFF2013-03Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)support from SR16000 supercomputing resources of the Center for Computational Materials Science,Tohoku University.
文摘Emergent Dirac fermion states underlie many intriguing properties of graphene,and the search for them constitutes one strong motivation to explore two-dimensional(2D)allotropes of other elements.Phosphorene,the ultrathin layers of black phosphorous,has been a subject of intense investigations recently,and it was found that other group-Va elements could also form 2D layers with similar puckered lattice structure.Here,by a close examination of their electronic band structure evolution,we discover two types of Dirac fermion states emerging in the low-energy spectrum.One pair of(type-I)Dirac points is sitting on high-symmetry lines,while two pairs of(type-II)Dirac points are located at generic k-points,with different anisotropic dispersions determined by the reduced symmetries at their locations.Such fully-unpinned(type-II)2D Dirac points are discovered for the first time.In the absence of spin-orbit coupling(SOC),we find that each Dirac node is protected by the sublattice symmetry from gap opening,which is in turn ensured by any one of three point group symmetries.The SOC generally gaps the Dirac nodes,and for the type-I case,this drives the system into a quantum spin Hall insulator phase.We suggest possible ways to realise the unpinned Dirac points in strained phosphorene.
基金This work was supported by the Science and Technology Development Fund(FDCT)from Macao SAR(0081/2019/AMJ,0102/2019/A2,and 0154/2019/A3)。
文摘Two-dimensional (2D) multiferroics have attracted increasing interests in basic science and technological fields in recent years.However,most reported 2D magnetic ferroelectrics are based on the d-electron magnetism,which makes them rather rare due to the empirical d^(0) rule and limits their applications for low magnetic phase transition temperature.In this work,we demonstrate that the ferroelectricity can coexist with the p-electron-induced ferromagnetism without the limitation of d^(0) rule and metallicity in a family of stable 2D MXene-analogous oxynitrides,X_(2)NO_(2) (X = In,Tl).Remarkably,the itinerant character of p electrons can lead to the strong ferromagnetic metallic states.Furthermore,a possible magnetoelectric effect is manifested in a Tl_(2)NO_(2)/WTe_(2) heterostructure through the interface engineering.Our findings provide an alternative possible route toward 2D multiferroics and enrich the concept of ferroelectric metals.
