Searching for one-dimensional(1D)nanostructure with ferromagnetic(FM)half-metallicity is of significance for the development of miniature spintronic devices.Here,based on the first-principles calculations,we propose t...Searching for one-dimensional(1D)nanostructure with ferromagnetic(FM)half-metallicity is of significance for the development of miniature spintronic devices.Here,based on the first-principles calculations,we propose that the 1D CrN nanostructure is a FM half-metal,which can generate the fully spin-polarized current.The ab initio molecular dynamic simulation and the phonon spectrum calculation demonstrate that the 1D CrN nanostructure is thermodynamically stable.The partially occupied Cr-d orbitals endow the nanostructure with FM half-metallicity,in which the half-metallic gap(?s)reaches up to 1.58 eV.The ferromagnetism in the nanostructure is attributed to the superexchange interaction between the magnetic Cr atoms,and a sizable magnetocrystalline anisotropy energy(MAE)is obtained.Moreover,the transverse stretching of nanostructure can effectively modulate?s and MAE,accompanied by the preservation of half-metallicity.A nanocable is designed by encapsulating the CrN nanostructure with a BN nanotube,and the intriguing magnetic and electronic properties of the nanostructure are retained.These novel characteristics render the 1D CrN nanostructure as a compelling candidate for exploiting high-performance spintronic devices.展开更多
Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without chang-ing their composition.In this work,we investigate the electronic,optical,and mechanical properties of...Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without chang-ing their composition.In this work,we investigate the electronic,optical,and mechanical properties of antiperovskite X_(3)NP(X^(2+)=Ca,Mg)upon compression by first-principles calculations.Our results reveal that the system is anisotropic,and the lat-tice constant a of X_(3)NP exhibits the fastest rate of decrease upon compression among the three directions,which is different from the typical Pnma phase of halide and chalcogenide perovskites.Meanwhile,Ca_(3)NP has higher compressibility than Mg_(3)NP due to its small bulk modulus.The electronic and optical properties of Mg_(3)NP show small fluctuations upon compression,but those of Ca_(3)NP are more sensitive to pressure due to its higher compressibility and lower unoccupied 3d orbital energy.For example,the band gap,lattice dielectric constant,and exciton binding energy of Ca_(3)NP decrease rapidly as the pressure increases.In addition,the increase in pressure significantly improves the optical absorption and theoretical conversion effi-ciency of Ca_(3)NP.Finally,the mechanical properties of X_(3)NP are also increased upon compression due to the reduction in bond length,while inducing a brittle-to-ductile transition.Our research provides theoretical guidance and insights for future experi-mental tuning of the physical properties of antiperovskite semiconductors by pressure.展开更多
In our previous work [1], a new kind of inflation model was proposed, which has the interesting property that its perturbation equation of motion gets a correction of k4, due to the non-linearity of the kinetic term.N...In our previous work [1], a new kind of inflation model was proposed, which has the interesting property that its perturbation equation of motion gets a correction of k4, due to the non-linearity of the kinetic term.Nonetheless, the scale-invariance of the power spectrum remains valid, both in large-k and small-k limits. In this paper, we investigate in detail the spectral index, the index running and the tensor/scalar ratio in this model, especially in the potential-driven case, and compare the results with the current PLANCK/BICEP observational data.We also discuss the tensor spectrum in this case, which is expected to be tested by future observations of primordial gravitational waves.展开更多
Topological insulators(TIs)are considered as ideal platforms for generating large spin Hall conductivity(SHC),however,the bulk carrier problem,which is unavoidable in TIs,hinders their practical applications.Recently,...Topological insulators(TIs)are considered as ideal platforms for generating large spin Hall conductivity(SHC),however,the bulk carrier problem,which is unavoidable in TIs,hinders their practical applications.Recently,topological semimetals(TSMs)have been proposed to achieve large SHC to replace TIs.However,the ideal TSM candidates with large SHC are still lacking.In terms of firstprinciples calculations,we predict that Ta3As family compounds exhibit complex crossing nodal-lines(CNL)properties in absence of the spin-orbit coupling(SOC).However,they transfer to Dirac TSMs under the influence of strong SOC,and present large SHC around Fermi level in particular.Remarkably,the SHC value of Ta_(3)Y(Y=As,Sb,Bi)is around 1500–1700 e/h=eTeΩ·cmT^(-1),which is comparable to noble metal Pt and much larger than TIs,Weyl TSMs,and 4d/5d transition metals.Our work not only suggests a kind of TSM family with interesting Dirac CNL around Fermi level,but also paves the way for searching large intrinsic SHC materials in complex CNL TSM systems.展开更多
基金the National Natural Science Foundation of China(Grant Nos.12004137,62071200,and 12104236)Shandong Provincial Natural Science Foundation of China(Grant Nos.ZR2020QA052,ZR2020ZD28,ZR2021MA040,and ZR2021MA060).
文摘Searching for one-dimensional(1D)nanostructure with ferromagnetic(FM)half-metallicity is of significance for the development of miniature spintronic devices.Here,based on the first-principles calculations,we propose that the 1D CrN nanostructure is a FM half-metal,which can generate the fully spin-polarized current.The ab initio molecular dynamic simulation and the phonon spectrum calculation demonstrate that the 1D CrN nanostructure is thermodynamically stable.The partially occupied Cr-d orbitals endow the nanostructure with FM half-metallicity,in which the half-metallic gap(?s)reaches up to 1.58 eV.The ferromagnetism in the nanostructure is attributed to the superexchange interaction between the magnetic Cr atoms,and a sizable magnetocrystalline anisotropy energy(MAE)is obtained.Moreover,the transverse stretching of nanostructure can effectively modulate?s and MAE,accompanied by the preservation of half-metallicity.A nanocable is designed by encapsulating the CrN nanostructure with a BN nanotube,and the intriguing magnetic and electronic properties of the nanostructure are retained.These novel characteristics render the 1D CrN nanostructure as a compelling candidate for exploiting high-performance spintronic devices.
基金supported by the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No. KJQN202100626)the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No. KJQN202200619)+3 种基金supported by Beijing Institute of Technology Research Fund Program for Young Scholars (Grant No. XSQD-202222008)the support from the National Natural Science Foundation of China (Grant No. 12204081)the Natural Science Foundation of Chongqing (Grant No. 2022NSCQ-MSX2540)supported by TianHe Qingsuo Project-spec ial fund project
文摘Hydrostatic pressure provides an efficient way to tune and optimize the properties of solid materials without chang-ing their composition.In this work,we investigate the electronic,optical,and mechanical properties of antiperovskite X_(3)NP(X^(2+)=Ca,Mg)upon compression by first-principles calculations.Our results reveal that the system is anisotropic,and the lat-tice constant a of X_(3)NP exhibits the fastest rate of decrease upon compression among the three directions,which is different from the typical Pnma phase of halide and chalcogenide perovskites.Meanwhile,Ca_(3)NP has higher compressibility than Mg_(3)NP due to its small bulk modulus.The electronic and optical properties of Mg_(3)NP show small fluctuations upon compression,but those of Ca_(3)NP are more sensitive to pressure due to its higher compressibility and lower unoccupied 3d orbital energy.For example,the band gap,lattice dielectric constant,and exciton binding energy of Ca_(3)NP decrease rapidly as the pressure increases.In addition,the increase in pressure significantly improves the optical absorption and theoretical conversion effi-ciency of Ca_(3)NP.Finally,the mechanical properties of X_(3)NP are also increased upon compression due to the reduction in bond length,while inducing a brittle-to-ductile transition.Our research provides theoretical guidance and insights for future experi-mental tuning of the physical properties of antiperovskite semiconductors by pressure.
基金Supported by NSFC(11405069,11653002,11735007,111375070)
文摘In our previous work [1], a new kind of inflation model was proposed, which has the interesting property that its perturbation equation of motion gets a correction of k4, due to the non-linearity of the kinetic term.Nonetheless, the scale-invariance of the power spectrum remains valid, both in large-k and small-k limits. In this paper, we investigate in detail the spectral index, the index running and the tensor/scalar ratio in this model, especially in the potential-driven case, and compare the results with the current PLANCK/BICEP observational data.We also discuss the tensor spectrum in this case, which is expected to be tested by future observations of primordial gravitational waves.
基金The authors thank Bin Huang and Bin Cui for the helpful discussions.We acknowledge the National Key R&D Program of China(2018YFB0407602)Beijing Municipal Science and Technology Project under Grant Z201100004220002+5 种基金the Fundamental Research Funds for the Central Universities and the China Postdoctoral Science Foundation(No.2020M670083,2020M672039)the National Natural Science Foundation of China(Grant Nos.61627813,61571023,11674139,11674317,11974348,11834014,11834005)the Strategic Priority Research Program of CAS(Grant No.XDB28000000 and No.XDB33000000)the National Key Technology Program of China(Grant No.2017ZX01032101)the Special Foundation for Theoretical Physics Research Program of China(No.11947207)for their financial support of this work.Parts of the calculations were performed at Tianhe2-JK at CSRC.
文摘Topological insulators(TIs)are considered as ideal platforms for generating large spin Hall conductivity(SHC),however,the bulk carrier problem,which is unavoidable in TIs,hinders their practical applications.Recently,topological semimetals(TSMs)have been proposed to achieve large SHC to replace TIs.However,the ideal TSM candidates with large SHC are still lacking.In terms of firstprinciples calculations,we predict that Ta3As family compounds exhibit complex crossing nodal-lines(CNL)properties in absence of the spin-orbit coupling(SOC).However,they transfer to Dirac TSMs under the influence of strong SOC,and present large SHC around Fermi level in particular.Remarkably,the SHC value of Ta_(3)Y(Y=As,Sb,Bi)is around 1500–1700 e/h=eTeΩ·cmT^(-1),which is comparable to noble metal Pt and much larger than TIs,Weyl TSMs,and 4d/5d transition metals.Our work not only suggests a kind of TSM family with interesting Dirac CNL around Fermi level,but also paves the way for searching large intrinsic SHC materials in complex CNL TSM systems.