Surface-sensitive electronic structure of kagome superconductor CsV_(3)Sb_(5)

We systematically study the electronic structure of a kagome superconductor CsV_(3)Sb_(5)at different temperatures coveringboth its charge density wave state and normal state with angle-resolved photoemission spectroscopy.We observe thatthe V-shaped band aroundГshows three different behaviors,referred to as a/a',βandγ,mainly at different temperatures.Detailed investigations confirm that these bands are all from the same bulk Sb-p_(z)origin,but they are quite sensitiveto the sample surface conditions mainly modulated by temperature.Thus,the intriguing temperature dependent electronicbehavior of the band nearГis affected by the sample surface condition,rather than intrinsic electronic behavior originatingfrom the phase transition.Our result systematically reveals the confusing electronic structure behavior of the energy bandsaroundГ,facilitating further exploration of the novel properties in this material.

Encoding innumerable charge density waves of FeGe into polymorphs of LiFe_(6)Ge_(6)

Kagome metals exhibit rich quantum states by the intertwining of lattice,charge,orbital and spin degrees of freedom.Recently,a novel charge density wave(CDW)ground state was discovered in kagome magnet FeGe and was revealed to be driven by lowering magnetic energy via large Ge1-dimerization.Here,based on DFTcalculations,we show that such mechanism will yield infinitely many metastable CDWs in FeGe due to different ways to arrange the Ge1-dimerization in enlarged superstructures.Intriguingly,utilizing these metastable CDWs,innumerable polymorphs of kagome magnet LiFe_(6)Ge_(6) can be stabilized by filling Li atoms in the voids right above/below the dimerized Ge1-sites in the CDW superstructures.Such polymorphs are very stable due to the presence of magnetic-energy-saving mechanism,in sharp contrast to the non-magnetic“166”kagome compounds.In this way,a one-to-one mapping of the metastable CDWs of FeGe to stable polymorphs of LiFe_(6)Ge_(6) is established.On one hand,the fingerprints of these metastable CDWs,i.e.,the induced in-plane atomic distortions and band gaps,are encoded into the corresponding stable polymorphs of LiFe_(6)Ge_(6),such that further study of their properties becomes possible.On the other hand,such innumerable polymorphs of LiFe_(6)Ge_(6) offer great degrees of freedom to explore the rich physics of magnetic kagome metals.We thus reveal a novel connection between the unusually abundant CDWs and structural polymorphism in magnetic kagome materials,and establish a new route to obtain structural polymorphism on top of CDW states.

范德华材料Ta_(2)Ni_(3)Te_(5)中巨大的面内振动和输运各向异性

目前,Ta_(2)M3Te_(5)(M=Ni,Pd)层状范德华化合物可承载各种奇异电子态,且具有表现出非平凡输运现象的诱人潜力,因而重新引起人们的兴趣.其特征有Luttinger液体、量子自旋霍尔效应、高阶拓扑结构和超导电性.本文中,我们报道了单晶Ta_(2)Ni_(3)Te_(5)的合成,并揭示了其在每个具有准一维键合特征的层内的多重平面内各向异性.我们的技术结合了偏振拉曼光谱、角度分辨光电发射光谱、第一性原理计算和电/磁输运测量的能力.链状低对称层状结构的声子振动产生了高度各向异性的拉曼响应,不同的链内和链间键合特性导致电子带和声学声子的各向异性色散,这共同导致[100]和[001]方向之间的巨大平面内迁移率各向异性(2000%).这一结果与我们的电输运和霍尔效应测量结果相符.因此,沿不同平面内方向的输运行为也表现出不同的温度和磁场依赖性.本工作揭示的丰富的面内各向异性表明,Ta_(2)Ni_(3)Te_(5)是探索新型二维各向异性电子动力学的一个很有前途的平台,在下一代纳米电子器件中具有潜在的应用前景.