Monolayer group-VIB transition metal dichalcogenides(TMDs)feature low-energy massive Dirac fermions,which have valley contrasting Berry curvature.This nontrivial local band topology gives rise to valley Hall transport...Monolayer group-VIB transition metal dichalcogenides(TMDs)feature low-energy massive Dirac fermions,which have valley contrasting Berry curvature.This nontrivial local band topology gives rise to valley Hall transport and optical selection rules for interband transitions that open up new possibilities for valleytronics.However,the large bandgap in TMDs results in relatively small Berry curvature,leading to weak valley contrasting physics in practical experiments.Here,we show that Dirac fermions with tunable large Berry curvature can be engineered in moirésuperlattice of TMD heterobilayers.These moiréDirac fermions are created in a magnified honeycomb lattice with its sublattice degree of freedom formed by two local moirépotential minima.We show that applying an on-site potential can tune the moiréflat bands into helical ones.In short-period moirésuperlattice,we find that the two moirévalleys become asymmetric,which results in a net spin Hall current.More interestingly,a circularly polarized light drives these moiréDirac fermions into quantum anomalous Hall phase with chiral edge states.Our results open a new possibility to design the moiré-scale spin and valley physics using TMD moiréstructures.展开更多
Van der Waals heterostructures(vdWHs)realized by vertically stacking of different two-dimensional(2D)materials are a promising candidate for tunneling devices because of their atomically clean and lattice mismatch-fre...Van der Waals heterostructures(vdWHs)realized by vertically stacking of different two-dimensional(2D)materials are a promising candidate for tunneling devices because of their atomically clean and lattice mismatch-free interfaces in which different layers are separated by the vdW gaps.The gaps can provide an ideal electric modulation environment on the vdWH band structures and,on the other hand,can also impede the electron tunneling behavior because of large tunneling widths.Here,through first-principles calculations,we find that the electrically modulated tunneling behavior is immune to the interlayer interaction,keeping a direct band-to-band tunneling manner even the vdWHs have been varied to the indirect semiconductor,which means that the tunneling probability can be promoted through the vdW gap shrinking.Using transition metal dichalcogenide heterostructures as examples and normal strains as the gap reducing strategy,a maximum shrinking of 33%is achieved without changing the direct tunneling manner,resulting in a tunneling probability promotion of more than 45 times.Furthermore,the enhanced interlayer interaction by the strains will boost the stability of the vdWHs at the lateral direction,preventing the interlayer displacement effectively.It is expected that our findings provide perspectives in improving the electric behaviors of the vdWH devices.展开更多
基金Project supported by the Science Fund for Distinguished Young Scholars of Hunan Province(Grant No.2022J10002)the National Key Research and Development Program of China(Grant No.2021YFA1200503)the Fundamental Research Funds for the Central Universities from China。
文摘Monolayer group-VIB transition metal dichalcogenides(TMDs)feature low-energy massive Dirac fermions,which have valley contrasting Berry curvature.This nontrivial local band topology gives rise to valley Hall transport and optical selection rules for interband transitions that open up new possibilities for valleytronics.However,the large bandgap in TMDs results in relatively small Berry curvature,leading to weak valley contrasting physics in practical experiments.Here,we show that Dirac fermions with tunable large Berry curvature can be engineered in moirésuperlattice of TMD heterobilayers.These moiréDirac fermions are created in a magnified honeycomb lattice with its sublattice degree of freedom formed by two local moirépotential minima.We show that applying an on-site potential can tune the moiréflat bands into helical ones.In short-period moirésuperlattice,we find that the two moirévalleys become asymmetric,which results in a net spin Hall current.More interestingly,a circularly polarized light drives these moiréDirac fermions into quantum anomalous Hall phase with chiral edge states.Our results open a new possibility to design the moiré-scale spin and valley physics using TMD moiréstructures.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2018YFB0406603 and 2018YFA0703704)the National Natural Science Foundation of China(Grant Nos.51991341,61904052,61851403 and 61704051)+1 种基金the Key Research and Development Plan of Hunan Province(Grant No.2018GK2064)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB30000000).
文摘Van der Waals heterostructures(vdWHs)realized by vertically stacking of different two-dimensional(2D)materials are a promising candidate for tunneling devices because of their atomically clean and lattice mismatch-free interfaces in which different layers are separated by the vdW gaps.The gaps can provide an ideal electric modulation environment on the vdWH band structures and,on the other hand,can also impede the electron tunneling behavior because of large tunneling widths.Here,through first-principles calculations,we find that the electrically modulated tunneling behavior is immune to the interlayer interaction,keeping a direct band-to-band tunneling manner even the vdWHs have been varied to the indirect semiconductor,which means that the tunneling probability can be promoted through the vdW gap shrinking.Using transition metal dichalcogenide heterostructures as examples and normal strains as the gap reducing strategy,a maximum shrinking of 33%is achieved without changing the direct tunneling manner,resulting in a tunneling probability promotion of more than 45 times.Furthermore,the enhanced interlayer interaction by the strains will boost the stability of the vdWHs at the lateral direction,preventing the interlayer displacement effectively.It is expected that our findings provide perspectives in improving the electric behaviors of the vdWH devices.
