Heterostructures composed of two-dimensional van der Waals(vdW)materials allow highly controllable stacking,where interlayer twist angles introduce a continuous degree of freedom to alter the electronic band structure...Heterostructures composed of two-dimensional van der Waals(vdW)materials allow highly controllable stacking,where interlayer twist angles introduce a continuous degree of freedom to alter the electronic band structures and excitonic physics.Motivated by the discovery of Mott insulating states and superconductivity in magic-angle bilayer graphene,the emerging research fields of“twistronics”and moiréphysics have aroused great academic interests in the engineering of optoelectronic properties and the exploration of new quantum phenomena,in which moirésuperlattice provides a pathway for the realization of artificial excitonic crystals.Here we systematically summarize the current achievements in twistronics and moiréexcitonic physics,with emphasis on the roles of lattice rotational mismatches and atomic registries.Firstly,we review the effects of the interlayer twist on electronic and photonic physics,particularly on exciton properties such as dipole moment and spin-valley polarization,through interlayer interactions and electronic band structures.We also discuss the exciton dynamics in vdW heterostructures with different twist angles,like formation,transport and relaxation processes,whose mechanisms are complicated and still need further investigations.Subsequently,we review the theoretical analysis and experimental observations of moirésuperlattice and moirémodulated excitons.Various exotic moiréeffects are also shown,including periodic potential,moiréminiband,and varying wave function symmetry,which result in exciton localization,emergent exciton peaks and spatially alternating optical selection rule.We further introduce the expanded properties of moirésystems with external modulation factors such as electric field,doping and strain,showing that moirélattice is a promising platform with high tunability for optoelectronic applications and in-depth study on frontier physics.Lastly,we focus on the rapidly developing field of correlated electron physics based on the moirésystem,which is potentially related to the emerging quantum phenomena.展开更多
We investigate the peak structure in the interlayer conductance of Moirésuperlattices using a tunneling theory wedeveloped previously.The theoretical results predict that,due to the resonance of two different par...We investigate the peak structure in the interlayer conductance of Moirésuperlattices using a tunneling theory wedeveloped previously.The theoretical results predict that,due to the resonance of two different partial waves,the doublepeakstructure can appear in the curve of the interlayer conductance versus twist angle.Furthermore,we study the influencesof the model parameters,i.e.,the chemical potential of electrodes,the thickness of Moirésuperlattice,and the strength ofinterface potential,on the peak structure of the interlayer conductance.In particular,the parameter dependence of the peakstructure is concluded via a phase diagram,and the physical meanings of the phase diagram is formulized.Finally,thepotential applications of the present work is discussed.展开更多
Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has ...Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has been attempted through ultra-thin films by such as molecular beam epitaxy. However, the revisiting of thin films becomes popular again, in another fashion of the isolation of freestanding 2D layers out of van der Waals (vdW) bulk compounds. To date, nearly two decades after the nativity of the great graphene venture, researchers are still fascinated about flattening, into the atomic limit, all kinds of crystals, whether or not they are vdW. In this introductive review, we will summarize some recent experimental progresses on 2D electronic systems, and briefly discuss their revolutionizing capabilities for the implementation of future nanostructures and nanoelectronics.展开更多
We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-par...We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-parity superconductor.Based on this,we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node.We show that mixed Rashba and Dresselhaus spin-orbit coupling and anisotropic hopping terms,which break the C_(4)symmetry of the Fermi surface,can induce first-order topological superconductors with non-zero bulk Chern number.This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential.We demonstrate our results using a typical twisted angle of 53.13°,at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moir′e momentum.展开更多
We study theoretically the construction of topological conducting domain walls with a finite width between AB/BA stacking regions via finite element method in bilayer graphene systems with tunable commensurate twistin...We study theoretically the construction of topological conducting domain walls with a finite width between AB/BA stacking regions via finite element method in bilayer graphene systems with tunable commensurate twisting angles.We find that the smaller is the twisting angle,the more significant the lattice reconstruction would be,so that sharper domain boundaries declare their existence.We subsequently study the quantum transport properties of topological zero-line modes which can exist because of the said domain boundaries via Green’s function method and Landauer–Büttiker formalism,and find that in scattering regions with triintersectional conducting channels,topological zero-line modes both exhibit robust behavior exemplified as the saturated total transmission Gtot≈2e_(2)/h and obey a specific pseudospin-conserving current partition law among the branch transport channels.The former property is unaffected by Aharonov–Bohm effect due to a weak perpendicular magnetic field,but the latter is not.Results from our genuine bilayer hexagonal system suggest a twisting angle aroundθ≈0.1°for those properties to be expected,consistent with the existing experimental reports.展开更多
基金The authors are grateful for financial support from the National Natural Science Foundation of China(Nos.62105364 and 62075240)the Science and Technology Innovation Program of Hunan Province(No.2021RC2068)the Scientific Researches Foundation of National University of Defense Technology(No.ZK22-16).
文摘Heterostructures composed of two-dimensional van der Waals(vdW)materials allow highly controllable stacking,where interlayer twist angles introduce a continuous degree of freedom to alter the electronic band structures and excitonic physics.Motivated by the discovery of Mott insulating states and superconductivity in magic-angle bilayer graphene,the emerging research fields of“twistronics”and moiréphysics have aroused great academic interests in the engineering of optoelectronic properties and the exploration of new quantum phenomena,in which moirésuperlattice provides a pathway for the realization of artificial excitonic crystals.Here we systematically summarize the current achievements in twistronics and moiréexcitonic physics,with emphasis on the roles of lattice rotational mismatches and atomic registries.Firstly,we review the effects of the interlayer twist on electronic and photonic physics,particularly on exciton properties such as dipole moment and spin-valley polarization,through interlayer interactions and electronic band structures.We also discuss the exciton dynamics in vdW heterostructures with different twist angles,like formation,transport and relaxation processes,whose mechanisms are complicated and still need further investigations.Subsequently,we review the theoretical analysis and experimental observations of moirésuperlattice and moirémodulated excitons.Various exotic moiréeffects are also shown,including periodic potential,moiréminiband,and varying wave function symmetry,which result in exciton localization,emergent exciton peaks and spatially alternating optical selection rule.We further introduce the expanded properties of moirésystems with external modulation factors such as electric field,doping and strain,showing that moirélattice is a promising platform with high tunability for optoelectronic applications and in-depth study on frontier physics.Lastly,we focus on the rapidly developing field of correlated electron physics based on the moirésystem,which is potentially related to the emerging quantum phenomena.
基金supported by the National Natural Science Foundation of China(Grant No.11704197)the Natural Science Foundation of Nanjing University of Posts and Telecommunications(Grant Nos.NY221066 and NY223074).
文摘We investigate the peak structure in the interlayer conductance of Moirésuperlattices using a tunneling theory wedeveloped previously.The theoretical results predict that,due to the resonance of two different partial waves,the doublepeakstructure can appear in the curve of the interlayer conductance versus twist angle.Furthermore,we study the influencesof the model parameters,i.e.,the chemical potential of electrodes,the thickness of Moirésuperlattice,and the strength ofinterface potential,on the peak structure of the interlayer conductance.In particular,the parameter dependence of the peakstructure is concluded via a phase diagram,and the physical meanings of the phase diagram is formulized.Finally,thepotential applications of the present work is discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974357 and U1932151)the State Key Research Development Program of China(Grant No.2019YFA0307800)+1 种基金the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices,China(Grant No.KF201816)the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC,China(Grant No.U1537204).
文摘Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has been attempted through ultra-thin films by such as molecular beam epitaxy. However, the revisiting of thin films becomes popular again, in another fashion of the isolation of freestanding 2D layers out of van der Waals (vdW) bulk compounds. To date, nearly two decades after the nativity of the great graphene venture, researchers are still fascinated about flattening, into the atomic limit, all kinds of crystals, whether or not they are vdW. In this introductive review, we will summarize some recent experimental progresses on 2D electronic systems, and briefly discuss their revolutionizing capabilities for the implementation of future nanostructures and nanoelectronics.
基金Project supported by the National Natural Science Foundation of China(Grant No.11974293)。
文摘We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-parity superconductor.Based on this,we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node.We show that mixed Rashba and Dresselhaus spin-orbit coupling and anisotropic hopping terms,which break the C_(4)symmetry of the Fermi surface,can induce first-order topological superconductors with non-zero bulk Chern number.This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential.We demonstrate our results using a typical twisted angle of 53.13°,at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moir′e momentum.
基金supported by the National Natural Science Foundation of China(Grant Nos.51672171,51861145315,11804216,and 11974327)The supercomputing services from AM-HPC,the Chinese Scholarship Council,Fundamental Research Funds for the Central Universities(Nos.WK3510000010 and WK2030020032),Anhui Initiative in Quantum Information Technologies.
文摘We study theoretically the construction of topological conducting domain walls with a finite width between AB/BA stacking regions via finite element method in bilayer graphene systems with tunable commensurate twisting angles.We find that the smaller is the twisting angle,the more significant the lattice reconstruction would be,so that sharper domain boundaries declare their existence.We subsequently study the quantum transport properties of topological zero-line modes which can exist because of the said domain boundaries via Green’s function method and Landauer–Büttiker formalism,and find that in scattering regions with triintersectional conducting channels,topological zero-line modes both exhibit robust behavior exemplified as the saturated total transmission Gtot≈2e_(2)/h and obey a specific pseudospin-conserving current partition law among the branch transport channels.The former property is unaffected by Aharonov–Bohm effect due to a weak perpendicular magnetic field,but the latter is not.Results from our genuine bilayer hexagonal system suggest a twisting angle aroundθ≈0.1°for those properties to be expected,consistent with the existing experimental reports.
