Machine learning(ML)integrated with density functional theory(DFT)calculations have recently been used to accelerate the design and discovery of single-atom catalysts(SACs)by establishing deep structure–activity rela...Machine learning(ML)integrated with density functional theory(DFT)calculations have recently been used to accelerate the design and discovery of single-atom catalysts(SACs)by establishing deep structure–activity relationships.The traditional ML models are always difficult to identify the structural differences among the single-atom systems with different modification methods,leading to the limitation of the potential application range.Aiming to the structural properties of several typical two-dimensional MA_(2)Z_(4)-based single-atom systems(bare MA_(2)Z_(4) and metal single-atom doped/supported MA_(2)Z_(4)),an improved crystal graph convolutional neural network(CGCNN)classification model was employed,instead of the traditional machine learning regression model,to address the challenge of incompatibility in the studied systems.The CGCNN model was optimized using crystal graph representation in which the geometric configuration was divided into active layer,surface layer,and bulk layer(ASB-GCNN).Through ML and DFT calculations,five potential single-atom hydrogen evolution reaction(HER)catalysts were screened from chemical space of 600 MA_(2)Z_(4)-based materials,especially V_(1)/HfSn_(2)N_(4)(S)with high stability and activity(Δ_(GH*)is 0.06 eV).Further projected density of states(pDOS)analysis in combination with the wave function analysis of the SAC-H bond revealed that the SAC-dz^(2)orbital coincided with the H-s orbital around the energy level of−2.50 eV,and orbital analysis confirmed the formation ofσbonds.This study provides an efficient multistep screening design framework of metal single-atom catalyst for HER systems with similar two-dimensional supports but different geometric configurations.展开更多
Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topologica...Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topological Dirac phases.It is a fundamental challenge to realize quantum transition between Z_2 nontrivial topological insulator（TI） and topological crystalline insulator（TCI） in one material because Z_2 TI and TCI have different requirements on the number of band inversions. The Z_2 TIs must have an odd number of band inversions over all the time-reversal invariant momenta, whereas the newly discovered TCIs, as a distinct class of the topological Dirac materials protected by the underlying crystalline symmetry, owns an even number of band inversions. Taking PbSnTe_2 alloy as an example, here we demonstrate that the atomic-ordering is an effective way to tune the symmetry of the alloy so that we can electrically switch between TCI phase and Z_2 TI phase in a single material. Our results suggest that the atomic-ordering provides a new platform towards the realization of reversibly switching between different topological phases to explore novel applications.展开更多
The concept of α-CT2 separation L-fuzzy subsets in L-fuzzy topological spaces is presented by taking the stratiform structure of L-fuzzy subsets as the point of departure,and its basic characterizations and some topo...The concept of α-CT2 separation L-fuzzy subsets in L-fuzzy topological spaces is presented by taking the stratiform structure of L-fuzzy subsets as the point of departure,and its basic characterizations and some topological properties are discussed,and the relation between it and other separateness is exposed,and the action is studied of α-CT2 separateness in N-compact spaces and N-paracompact spaces.展开更多
2H-MoS_(2) is a well-studied and promising non-noble metal electrocatalyst for heterogeneous reactions,such as the hydrogen evolution reaction(HER).The performance is largely limited by the chemically inert basal plan...2H-MoS_(2) is a well-studied and promising non-noble metal electrocatalyst for heterogeneous reactions,such as the hydrogen evolution reaction(HER).The performance is largely limited by the chemically inert basal plane,which is unfavorable for surface adsorption and reactions.Herein,we report a facile method to boost the HER activities of 2H-MoS_(2) by coupling with epitaxial Bi2Te3 topological insulator films.The as-obtained MoS_(2)/Bi2Te3/SrTiO3 catalyst exhibits prominent HER catalytic activities compared to that of pure MoS_(2) structures,with a 189 mV decrease in the overpotential required to reach a current density of 10 mA cm^(−2) and a low Tafel slope of 58 mV dec−1.Theoretical investigations suggest that the enhanced catalytic activity originates from the charge redistribution at the interface between the Bi2Te3topological insulator films and the MoS_(2) layer.The delocalized sp-derived topological surface states could denote electrons to the MoS_(2) layer and activate the basal plane for hydrogen adsorption.This study demonstrates the potential of manipulating topological surface states to design high-performance electrocatalysts.展开更多
This paper presents an overview of the growth of Bi2Se3, a prototypical three-dimensional topological insulator, by molecular-beam epitaxy on various substrates. Comparison is made between the growth of Bi2 Se3 （111...This paper presents an overview of the growth of Bi2Se3, a prototypical three-dimensional topological insulator, by molecular-beam epitaxy on various substrates. Comparison is made between the growth of Bi2 Se3 （111） on van der Waals （vdW） and non-vdW substrates, with attention paid to twin suppression and strain. Growth along the [221] direction of Bi2Se3 on InP （001） and GaAs （001） substrates is also discussed.展开更多
Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetr...Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetric PbTaS2 is a topological nodal line semimetal. In the absence of spin-orbit coupling （SOC）, one band inversion happens around a high symmetrical H point, which leads to forming a nodal line. The nodal line is robust and protected against gap opening by mirror reflection symmetry even with the inclusion of strong SOC. In addition, it also hosts exotic drumhead surface states either inside or outside the projected nodal ring depending on surface termination. The robust bulk nodal lines and drumhead-like surface states with SOC in PbTaS2 make it a potential candidate material for exploring the freakish properties of the topological nodal line fermions in condensed matter systems.展开更多
Topological insulators are insulating in the bulkbut have metallic surface states. Its unique physicochemicalproperties can find numerous applications in electronics,spintronics, photonics, the energy sciences, and th...Topological insulators are insulating in the bulkbut have metallic surface states. Its unique physicochemicalproperties can find numerous applications in electronics,spintronics, photonics, the energy sciences, and thesignal control of transportation. We report an experimentalapproach to synthesize the high-quality single crystal oftopological insulator Bi2Te3 by using self-flux method. Weobtained the optimal preparation conditions by adjustingthe parameters of heat treatment, and successfully preparedthe single-crystal Bi2Te3 sample. The as-grown sampleshave a surface with bright metallic luster and are soft andfragile. Furthermore, Bi2Te3 has the obvious layer structurefrom SEM results. The data of X-ray diffraction andscanning electron microscope show that Bi2Te3 singlecrystal grows along the c-axis with the order of Te（1）–Bi–Te（2）–Bi–Te（1） and crystallizes in the hexagonal systemwith space group of R/3 m. The q–T curve shows that qdecreases with temperature, showing metallic behaviorover the whole temperature range.展开更多
High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7K. Combined with theoretical calculations, we discover for th...High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7K. Combined with theoretical calculations, we discover for the first time the existence of topologically nontrivial surface state with Dirac cone in PbTe2 superconductor. It is located at the Brillouin zone center and possesses helical spin texture. Distinct from the usual three-dimensional topological insulators where the Dirac cone of the surface state lies at the Fermi level, the Dirac point of the surface state in PdTe2 lies deeply below the Fermi level at - 1.75 eV binding energy and is well separated from the bulk states. The identification of topological surface state in PdTe2 superconductor deeply below the Fermi level provides a unique system to explore new phenomena and properties and opens a door for finding new topological materials in transition metal ehalcogenides.展开更多
After the discovery of fraction quantum Hall states in the 1980s, it became more and more clear that Landau symmetry breaking theory does not describe all possible quantum phases of matter. The new quan- tum phases of...After the discovery of fraction quantum Hall states in the 1980s, it became more and more clear that Landau symmetry breaking theory does not describe all possible quantum phases of matter. The new quan- tum phases of matter were called topologically ordered phases（for gapped cases） or quantum ordered phases （for gapless cases）, which correspond to pat- terns of many-body entanglement. One may won- der： besides quantum Hall systems, are there other systems that realize the new topological/quantum order？展开更多
Two new alkaline earth metal coordination polymers constructed from the deriva-tive of 1,2,4-triazole are presented herein,namely,{[Sr（AmTAZAc）2（H2O）]}（1） and {[Ba（AmTAZAc）2（H2O）]}（2）（AmTAZAc = 3-amino-1H...Two new alkaline earth metal coordination polymers constructed from the deriva-tive of 1,2,4-triazole are presented herein,namely,{[Sr（AmTAZAc）2（H2O）]}（1） and {[Ba（AmTAZAc）2（H2O）]}（2）（AmTAZAc = 3-amino-1H-1,2,4-triazole-5-carboxylate）,which have been synthesized by using the layering method and structurally characterized by elemental analysis,IR,and single-crystal X-ray diffraction.Complexes 1 and 2 are isostructural,and both crystallize in the orthorhombic system,space group Fdd2.X-ray structural analysis shows that 1 or 2 has an intriguing 3-D infinite network of（318.438.510） topology based on a 2-D sheet structure of（4,4） net.The result shows that noncovalent interactions play an important role in strengthening the whole structures of the compounds.展开更多
This paper is mainly concerned with corank-2 and corank-3 symmetrybreaking bifurcation point in Z2×Z2-symmetric nonlinear problems. Regular extended systems are used to compute corank-2 and corank-3 symmetry--bre...This paper is mainly concerned with corank-2 and corank-3 symmetrybreaking bifurcation point in Z2×Z2-symmetric nonlinear problems. Regular extended systems are used to compute corank-2 and corank-3 symmetry--breaking bifurcation points. Two numerical examples are given. In addition, we show that there exist three quadratic pitchfork bifurcation point curves passing through corank-2 symmetry breaking bifurcation point.展开更多
In this paper, a presented definition of type-2 fuzzy sets and type-2 fuzzy set operation on it was given. The aim of this work was to introduce the concept of general topological spaces were extended in type-2 fuzzy ...In this paper, a presented definition of type-2 fuzzy sets and type-2 fuzzy set operation on it was given. The aim of this work was to introduce the concept of general topological spaces were extended in type-2 fuzzy sets with the structural properties such as open sets, closed sets, interior, closure and neighborhoods in topological spaces were extended to general type-2 fuzzy topological spaces and many related theorems are proved.展开更多
Monolayer molybdenum disulfide(MoS2)has a honeycomb crystal structure.Here,with considering the triangular sublattice of molybdenum atoms,a simple tight-binding Hamiltonian is introduced(derived)for studying the phase...Monolayer molybdenum disulfide(MoS2)has a honeycomb crystal structure.Here,with considering the triangular sublattice of molybdenum atoms,a simple tight-binding Hamiltonian is introduced(derived)for studying the phase transition and topological superconductivity in MoS2 under uniaxial strain.It is shown that spin-singlet p+ip wave phase is a topological superconducting phase with nonzero Chern numbers.When the chemical potential is greater(smaller)than the spin-orbit coupling(SOC)strength,the Chern number is equal to four(two)and otherwise it is equal to zero.Also,the results show that,if the superconductivity energy gap is smaller than the SOC strength and the chemical potential is greater than the SOC strength,the zero energy Majorana states exist.Finally,we show that the topological superconducting phase is preserved under uniaxial strain.展开更多
A two-dimensional(2D)MA_(2)Z_(4)family with and phases has been attracting tremendous interest,the MoSi_(2)N_(4)and WSi_(2)N_(4)of which have been successfully fabricated(Science 369,670(2020)).Janus monolayers have b...A two-dimensional(2D)MA_(2)Z_(4)family with and phases has been attracting tremendous interest,the MoSi_(2)N_(4)and WSi_(2)N_(4)of which have been successfully fabricated(Science 369,670(2020)).Janus monolayers have been achieved in many 2D families,so it is interesting to construct a Janus monolayer from the MA_(2)Z_(4)family.In this work,Janus MSiGeN4(M=Zr and Hf)monolayers are predicted from-MA_(2)Z_(4),which exhibit dynamic,mechanical and thermal stabilities.It is found that they are indirect band-gap semiconductors by using generalized gradient approximation(GGA)plus spin-orbit coupling(SOC).With biaxial strain a/a0 from 0.90 to 1.10,the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum(CBM).A semiconductor to metal transition can be induced by both compressive and tensile strains,and the phase trans-formation point is about 0.96 for compressive strain and 1.10 for tensile strain.The tensile strain can change the positions of CBM and valence band maximum(VBM),and can also induce the weak Rashba-type spin splitting near CBM.For MSiGeN4(M=Zr and Hf)monolayers,both an in-plane and out-of-plane piezoelectric response can be produced,when a uniaxial strain in the basal plane is applied,which reveals the potential as piezoelectric 2D materials.The high absorption coefficients in the visible light region suggest that MSiGeN4(M=Zr and Hf)monolayers have potential photocatalytic applications.Our works provide an idea to achieve a Janus structure from the MA_(2)Z_(4)family,and can hopefully inspire further research exploring Janus MA_(2)Z_(4)monolayers.展开更多
基金supported by the National Key R&D Program of China(2021YFA1500900)National Natural Science Foundation of China(U21A20298,22141001).
文摘Machine learning(ML)integrated with density functional theory(DFT)calculations have recently been used to accelerate the design and discovery of single-atom catalysts(SACs)by establishing deep structure–activity relationships.The traditional ML models are always difficult to identify the structural differences among the single-atom systems with different modification methods,leading to the limitation of the potential application range.Aiming to the structural properties of several typical two-dimensional MA_(2)Z_(4)-based single-atom systems(bare MA_(2)Z_(4) and metal single-atom doped/supported MA_(2)Z_(4)),an improved crystal graph convolutional neural network(CGCNN)classification model was employed,instead of the traditional machine learning regression model,to address the challenge of incompatibility in the studied systems.The CGCNN model was optimized using crystal graph representation in which the geometric configuration was divided into active layer,surface layer,and bulk layer(ASB-GCNN).Through ML and DFT calculations,five potential single-atom hydrogen evolution reaction(HER)catalysts were screened from chemical space of 600 MA_(2)Z_(4)-based materials,especially V_(1)/HfSn_(2)N_(4)(S)with high stability and activity(Δ_(GH*)is 0.06 eV).Further projected density of states(pDOS)analysis in combination with the wave function analysis of the SAC-H bond revealed that the SAC-dz^(2)orbital coincided with the H-s orbital around the energy level of−2.50 eV,and orbital analysis confirmed the formation ofσbonds.This study provides an efficient multistep screening design framework of metal single-atom catalyst for HER systems with similar two-dimensional supports but different geometric configurations.
基金Supported by the Major State Basic Research Development Program of China under Grant No 2016YFB0700700the National Natural Science Foundation of China(NSFC)under Grants Nos 11634003,11474273,61121491 and U1530401+1 种基金supported by the National Young 1000 Talents Plansupported by the Youth Innovation Promotion Association of CAS(2017154)
文摘Topological phase transition in a single material usually refers to transitions between a trivial band insulator and a topological Dirac phase, and the transition may also occur between different classes of topological Dirac phases.It is a fundamental challenge to realize quantum transition between Z_2 nontrivial topological insulator（TI） and topological crystalline insulator（TCI） in one material because Z_2 TI and TCI have different requirements on the number of band inversions. The Z_2 TIs must have an odd number of band inversions over all the time-reversal invariant momenta, whereas the newly discovered TCIs, as a distinct class of the topological Dirac materials protected by the underlying crystalline symmetry, owns an even number of band inversions. Taking PbSnTe_2 alloy as an example, here we demonstrate that the atomic-ordering is an effective way to tune the symmetry of the alloy so that we can electrically switch between TCI phase and Z_2 TI phase in a single material. Our results suggest that the atomic-ordering provides a new platform towards the realization of reversibly switching between different topological phases to explore novel applications.
文摘The concept of α-CT2 separation L-fuzzy subsets in L-fuzzy topological spaces is presented by taking the stratiform structure of L-fuzzy subsets as the point of departure,and its basic characterizations and some topological properties are discussed,and the relation between it and other separateness is exposed,and the action is studied of α-CT2 separateness in N-compact spaces and N-paracompact spaces.
基金This work was financially supported by the European Research Council(ERC Advanced Grant No.291472'Idea Heusler1)and the ERC Advanced Grant(No.742068)TOPMAT.K.C.was funded by the National Natural Science Foundation of China(Grant No.12074038)J.H.and S.P.were supported by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)No.314790414.
文摘2H-MoS_(2) is a well-studied and promising non-noble metal electrocatalyst for heterogeneous reactions,such as the hydrogen evolution reaction(HER).The performance is largely limited by the chemically inert basal plane,which is unfavorable for surface adsorption and reactions.Herein,we report a facile method to boost the HER activities of 2H-MoS_(2) by coupling with epitaxial Bi2Te3 topological insulator films.The as-obtained MoS_(2)/Bi2Te3/SrTiO3 catalyst exhibits prominent HER catalytic activities compared to that of pure MoS_(2) structures,with a 189 mV decrease in the overpotential required to reach a current density of 10 mA cm^(−2) and a low Tafel slope of 58 mV dec−1.Theoretical investigations suggest that the enhanced catalytic activity originates from the charge redistribution at the interface between the Bi2Te3topological insulator films and the MoS_(2) layer.The delocalized sp-derived topological surface states could denote electrons to the MoS_(2) layer and activate the basal plane for hydrogen adsorption.This study demonstrates the potential of manipulating topological surface states to design high-performance electrocatalysts.
基金supported by the Research Grant Council (RGC) of Hong Kong Special Administrative Region for its financial support under the General Research Funds (Grant Nos. 706110 and 706111)the SRFDP and RGCERG Joint Research Scheme sponsored by the RGC of Hong Kong and the Ministry of Education of China (M-HKU709/l2)
文摘This paper presents an overview of the growth of Bi2Se3, a prototypical three-dimensional topological insulator, by molecular-beam epitaxy on various substrates. Comparison is made between the growth of Bi2 Se3 （111） on van der Waals （vdW） and non-vdW substrates, with attention paid to twin suppression and strain. Growth along the [221] direction of Bi2Se3 on InP （001） and GaAs （001） substrates is also discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 11504366the National Basic Research Program of China under Grant Nos 2015CB921503 and 2016YFE0110000
文摘Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetric PbTaS2 is a topological nodal line semimetal. In the absence of spin-orbit coupling （SOC）, one band inversion happens around a high symmetrical H point, which leads to forming a nodal line. The nodal line is robust and protected against gap opening by mirror reflection symmetry even with the inclusion of strong SOC. In addition, it also hosts exotic drumhead surface states either inside or outside the projected nodal ring depending on surface termination. The robust bulk nodal lines and drumhead-like surface states with SOC in PbTaS2 make it a potential candidate material for exploring the freakish properties of the topological nodal line fermions in condensed matter systems.
基金supported by the National Magnetic Confinement Fusion Science Program (Grant No. 2011GB112001)the Program of International S&T Cooperation (Grant No. 2013DFA 51050)+3 种基金the National Natural Science Foundation of China (Grant No. 11104224, 11004162, 51271155)the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20110184120029)the Fundamental Research Funds for the Central Universities (Grant No. 2682013ZT16, SWJTU11ZT31, 2682013CX004, SWJTU11BR063)the Science Foundation of Sichuan Province (Grant No. 2011JY0031, 2011JY0130)
文摘Topological insulators are insulating in the bulkbut have metallic surface states. Its unique physicochemicalproperties can find numerous applications in electronics,spintronics, photonics, the energy sciences, and thesignal control of transportation. We report an experimentalapproach to synthesize the high-quality single crystal oftopological insulator Bi2Te3 by using self-flux method. Weobtained the optimal preparation conditions by adjustingthe parameters of heat treatment, and successfully preparedthe single-crystal Bi2Te3 sample. The as-grown sampleshave a surface with bright metallic luster and are soft andfragile. Furthermore, Bi2Te3 has the obvious layer structurefrom SEM results. The data of X-ray diffraction andscanning electron microscope show that Bi2Te3 singlecrystal grows along the c-axis with the order of Te（1）–Bi–Te（2）–Bi–Te（1） and crystallizes in the hexagonal systemwith space group of R/3 m. The q–T curve shows that qdecreases with temperature, showing metallic behaviorover the whole temperature range.
基金the National Natural Science Foundation of China under Grant Nos 11190022,11274359 and 11422428the National Basic Research Program of China under Grant Nos 2011CB921703,2011CBA00110,2011CBA00108 and 2013CB921700the Strategic Priority Research Program(B)of the Chinese Academy of Sciences under Grant Nos XDB07020300 and XDB07020100
文摘High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7K. Combined with theoretical calculations, we discover for the first time the existence of topologically nontrivial surface state with Dirac cone in PbTe2 superconductor. It is located at the Brillouin zone center and possesses helical spin texture. Distinct from the usual three-dimensional topological insulators where the Dirac cone of the surface state lies at the Fermi level, the Dirac point of the surface state in PdTe2 lies deeply below the Fermi level at - 1.75 eV binding energy and is well separated from the bulk states. The identification of topological surface state in PdTe2 superconductor deeply below the Fermi level provides a unique system to explore new phenomena and properties and opens a door for finding new topological materials in transition metal ehalcogenides.
文摘After the discovery of fraction quantum Hall states in the 1980s, it became more and more clear that Landau symmetry breaking theory does not describe all possible quantum phases of matter. The new quan- tum phases of matter were called topologically ordered phases（for gapped cases） or quantum ordered phases （for gapless cases）, which correspond to pat- terns of many-body entanglement. One may won- der： besides quantum Hall systems, are there other systems that realize the new topological/quantum order？
基金Supported by the National Natural Science Foundation of China (Nos. 20771006 and 20901004)
文摘Two new alkaline earth metal coordination polymers constructed from the deriva-tive of 1,2,4-triazole are presented herein,namely,{[Sr（AmTAZAc）2（H2O）]}（1） and {[Ba（AmTAZAc）2（H2O）]}（2）（AmTAZAc = 3-amino-1H-1,2,4-triazole-5-carboxylate）,which have been synthesized by using the layering method and structurally characterized by elemental analysis,IR,and single-crystal X-ray diffraction.Complexes 1 and 2 are isostructural,and both crystallize in the orthorhombic system,space group Fdd2.X-ray structural analysis shows that 1 or 2 has an intriguing 3-D infinite network of（318.438.510） topology based on a 2-D sheet structure of（4,4） net.The result shows that noncovalent interactions play an important role in strengthening the whole structures of the compounds.
文摘This paper is mainly concerned with corank-2 and corank-3 symmetrybreaking bifurcation point in Z2×Z2-symmetric nonlinear problems. Regular extended systems are used to compute corank-2 and corank-3 symmetry--breaking bifurcation points. Two numerical examples are given. In addition, we show that there exist three quadratic pitchfork bifurcation point curves passing through corank-2 symmetry breaking bifurcation point.
文摘In this paper, a presented definition of type-2 fuzzy sets and type-2 fuzzy set operation on it was given. The aim of this work was to introduce the concept of general topological spaces were extended in type-2 fuzzy sets with the structural properties such as open sets, closed sets, interior, closure and neighborhoods in topological spaces were extended to general type-2 fuzzy topological spaces and many related theorems are proved.
文摘Monolayer molybdenum disulfide(MoS2)has a honeycomb crystal structure.Here,with considering the triangular sublattice of molybdenum atoms,a simple tight-binding Hamiltonian is introduced(derived)for studying the phase transition and topological superconductivity in MoS2 under uniaxial strain.It is shown that spin-singlet p+ip wave phase is a topological superconducting phase with nonzero Chern numbers.When the chemical potential is greater(smaller)than the spin-orbit coupling(SOC)strength,the Chern number is equal to four(two)and otherwise it is equal to zero.Also,the results show that,if the superconductivity energy gap is smaller than the SOC strength and the chemical potential is greater than the SOC strength,the zero energy Majorana states exist.Finally,we show that the topological superconducting phase is preserved under uniaxial strain.
基金supported by Natural Science Basis Research Plan in Shaanxi Province of China(2021JM-456)。
文摘A two-dimensional(2D)MA_(2)Z_(4)family with and phases has been attracting tremendous interest,the MoSi_(2)N_(4)and WSi_(2)N_(4)of which have been successfully fabricated(Science 369,670(2020)).Janus monolayers have been achieved in many 2D families,so it is interesting to construct a Janus monolayer from the MA_(2)Z_(4)family.In this work,Janus MSiGeN4(M=Zr and Hf)monolayers are predicted from-MA_(2)Z_(4),which exhibit dynamic,mechanical and thermal stabilities.It is found that they are indirect band-gap semiconductors by using generalized gradient approximation(GGA)plus spin-orbit coupling(SOC).With biaxial strain a/a0 from 0.90 to 1.10,the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum(CBM).A semiconductor to metal transition can be induced by both compressive and tensile strains,and the phase trans-formation point is about 0.96 for compressive strain and 1.10 for tensile strain.The tensile strain can change the positions of CBM and valence band maximum(VBM),and can also induce the weak Rashba-type spin splitting near CBM.For MSiGeN4(M=Zr and Hf)monolayers,both an in-plane and out-of-plane piezoelectric response can be produced,when a uniaxial strain in the basal plane is applied,which reveals the potential as piezoelectric 2D materials.The high absorption coefficients in the visible light region suggest that MSiGeN4(M=Zr and Hf)monolayers have potential photocatalytic applications.Our works provide an idea to achieve a Janus structure from the MA_(2)Z_(4)family,and can hopefully inspire further research exploring Janus MA_(2)Z_(4)monolayers.
