Surface doping manipulation of the insulating ground states in Ta_(2)Pd_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5)

Manipulating emergent quantum phenomena is a key issue for understanding the underlying physics and contributing to possible applications.Here we study the evolution of insulating ground states of Ta_(2)Pu_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5) under in-situ surface potassium deposition via angle-resolved photoemission spectroscopy.Our results confirm the excitonic insulator character of Ta_(2)d_(3)Te_(5).Upon surface doping,the size of its global gap decreases obviously.After a deposition time of more than 7 min,the potassium atoms induce a metal-insulator phase transition and make the system recover to a normal state.In contrast,our results show that the isostructural compound Ta_(2)Ni_(3)Te_(5) is a conventional insulator.The size of its global gap decreases upon surface doping,but persists positive throughout the doping process.Our results not only confirm the excitonic origin of the band gap in Ta_(2)Pd_(3)Te_(5),but also offer an effective method for designing functional quantum devices in the future.

Ferromagnetic MnSn Monolayer Epitaxially Grown on Silicon Substrate

Two-dimensional(2D)ferromagnetic materials have been exhibiting promising potential in applications,such as spintronics devices.To grow epitaxial magnetic films on silicon substrate,in the single-layer limit,is practically important but challenging.In this study,we realized the epitaxial growth of Mn Sn monolayer on Si(111)substrate,with an atomically thin Sn/Si(111)-231/2×231/2-buffer layer,and controlled the Mn Sn thickness with atomic-layer precision.We discovered the ferromagnetism in Mn Sn monolayer with the Curie temperature(Tc)of^54 K.As the Mn Sn film is grown to 4 monolayers,Tc increases accordingly to^235 K.The lattice of the epitaxial Mn Sn monolayer as well as the Sn/Si(111)-231/2×231/2 is perfectly compatible with silicon,and thus an sharp interface is formed between Mn Sn,Sn and Si.This system provides a new platform for exploring the 2D ferromagnetism,integrating magnetic monolayers into silicon-based technology,and engineering the spintronics heterostructures.

钾氨电子化合物中的准二维自旋-派尔斯相变

Electron-phonon interactions and electron-electron correlations represent two crucial facets of condensed matter physics.For instance,in a half-filled spin-1/2 anti-ferromagnetic chain,the lattice dimerization induced by electron-nucleus interaction can be intensified by onsite Coulomb repulsion,resulting in a spin-Peierls state.Through first-principles calculations and crystal structure prediction methods,we have identified that under mild pressures,potassium and ammonia can form stable compounds:R3m K(NH_(3))_(2),Pm3 m K(NH_(3))_(2),and Cm K_(2)(NH_(3))_(3).Our predictions suggest that the R3 m K(NH_(3))_(2)exhibits electride characteristics,marked by the formation of interstitial anionic electrons(IAEs)in the interlayer space.These IAEs are arranged in quasi-two-dimensional triangular arrays.With increasing pressure,the electronic van-Hove singularity shifts toward the Fermi level,resulting in an augmented density of states and the onset of both Peierls and magnetic instabilities.Analyzing these instabilities,we determine that the ground state of the R3 m K(NH_(3))_(2)is the dimerized P2_(1)/m phase with zigzag-type anti-ferromagnetic IAEs.This state can be described by the triangular-lattice antiferromagnetic Heisenberg model with modulated magnetic interactions.Furthermore,we unveil the coexistence and positive interplay between magnetic and Peierls instability,constituting a scenario of spin-Peierls instability unprecedented in realistic 2D materials,particularly involving IAEs.This work provides valuable insights into the coupling of IAEs with the adjacent lattice and their spin correlations in quantum materials.

非常规材料:电子分布不在原子上

在拓扑量子化学中,研究人员发展了空间群下完备的基本能带表示,既对应于实空间的局域轨道,又对应于倒空间的一组不可约表示.通过计算实际材料的高对称k点的不可约表示,再利用基本能带表示分解来判断材料的拓扑性质.本研究发现拓扑平庸的材料可以分为电子电荷中心在原子上的常规材料和电荷中心不在原子上的“非常规材料”.这种非常规的电子分布特征在特定晶体对称群下可以方便地由能带表示分解来判断:占据态是基础能带表示的组合,但不是原子轨道对应的能带表示的组合.同时作者引入空位上的(必要)能带表示和实空间不变量来标定这一非常规电子分布特性.利用这一基于对称性本征值的能带表示分解方法,本文通过高通量搜索找到了423个非常规材料,并讨论了这些材料热电、储氢、催化、超导等特殊的化学性质与非常规电荷分布的相关性.