Experimental Observation of Electronic Structures of Kagome Metal YCr6Ge6

Using angle-resolved photoemission spectroscopy,we study electronic structures of a Kagome metal YCr6Ge6.Band dispersions along kz direction are significant,suggesting a remarkable interlayer coupling between neighboring Kagome planes.Comparing ARPES data with first-principles calculations,we find a moderate electron correlation in this material,since band calculations must be compressed in the energy scale to reach an excellent agreement between experimental data and theoretical calculations.Moreover,as indicated by band calculations,there is a flat band in the vicinity of the Fermi level at the Г–M–K plane in the momentum space,which could be responsible for the unusual transport behavior in YCr6Ge6.

Ni、Cr对钢液表面氮溶解速率的影响

采用氮同位素气体交换技术实验测定了Fe-Cr、Fe-Ni和Fe-Cr-Ni体系在1873 K时的氮溶解反应速率常数,分析讨论了Cr、Ni含量对氮溶解反应速率常数的影响,并计算获得了Cr和Ni的吸附系数。结果表明,随着钢液中Cr和Ni含量的增加,表面氮的溶解反应速率常数增大。在Fe-Cr-Ni体系中,Cr的吸附系数为-0.01,Ni的吸附系数为-0.03,氮溶解速率常数ka与Cr、Ni含量的关系式可表达为kα=4.53×10^-6/1(1-0.01[%Cr]-0.03[%Ni])2.

Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe_(2) film

As a special order of electronic correlation induced by spatial modulation, the charge density wave(CDW) phenomena in condensed matters attract enormous research interests. Here, using scanning-tunneling microscopy in various temperatures, we discover a hidden incommensurate stripe-like CDW order besides the(■) CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe_(2) film. Combining the variable-temperature angle-resolved photoemission spectroscopic(ARPES) measurements, we discover a two-step transition of an anisotropic CDW gap structure that consists of two parts △_(1) and△_(2). The gap part ?1 that closes around ~ 150 K is accompanied with the vanish of the(√7×√3) CDW phase. While another momentum-dependent gap part △_(2) can survive up to ~ 340 K, and is suggested to the result of the incommensurate CDW phase. This two-step transition with anisotropic gap opening and the resulted evolution in ARPES spectra are corroborated by our theoretical calculation based on a phenomenological form for the self-energy containing a two-gap structure △_(1) +△_(2), which suggests different forming mechanisms between the(√7×√3) and the incommensurate CDW phases. Our findings provide significant information and deep understandings on the CDW phases in monolayer 1T-VSe_(2) film as a two-dimensional(2D) material.

碳铝硅在铁液中对氮溶解速率的影响

通过15N-14N同位素气体交换技术消除液相传质的影响,利用在线质谱分析仪测定了在1873 K下,铁液中氮溶解的界面反应速率常数.结果表明,总流量为600~800 mL·min^−1时可以忽略气相传质的影响,保护气中增加H2的比例有利于降低钢液中杂质元素的浓度.铁液中加入一定量碳、铝、硅,分析得到这三种元素对氮溶解速率是抑制的.依据本实验的数据利用空位解离模型建立反应速率常数ka与氧、硫、碳、铝、硅的活度关系,吸附系数分别是KO=0.96,KS=9.32,KC=0.02,KAl=0.51,KSi=1.16.纯铁液中氮的溶解反应表观速率常数为ka=4.8×10^−6 mol·m^−2·s·Pa.

Molecular beam epitaxy growth of monolayer hexagonal MnTe_(2)on Si(111)substrate

Monolayer MnTe_(2)stabilized as 1 T structure has been theoretically predicted to be a two-dimensional(2 D)ferromagnetic metal and can be tuned via strain engineering.There is no naturally van der Waals(vdW)layered MnTe_(2)bulk,leaving mechanical exfoliation impossible to prepare monolayer MnTe_(2).Herein,by means of molecular beam epitaxy(MBE),we successfully prepared monolayer hexagonal MnTe_(2)on Si(111)under Te rich condition.Sharp reflection high-energy electron diffraction(RHEED)and low-energy electron diffraction(LEED)patterns suggest the monolayer is atomically flat without surface reconstruction.The valence state of Mn^(4+)and the atom ratio of([Te]:[Mn])further confirm the MnTe_(2)compound.Scanning tunneling spectroscopy(STS)shows the hexagonal MnTe_(2)monolayer is a semiconductor with a large bandgap of~2.78 eV.The valence-band maximum(VBM)locates at theΓpoint,as illustrated by angle-resolved photoemission spectroscopy(ARPES),below which three hole-type bands with parabolic dispersion can be identified.The successful synthesis of monolayer MnTe_(2)film provides a new platform to investigate the 2D magnetism.

Honeycomb Lattice in Metal-Rich Chalcogenide Fe_(2)Te

Two-dimensional honeycomb crystals have inspired intense research interest for their novel properties and great potential in electronics and optoelectronics. Here, through molecular beam epitaxy on SrTiO_3(001), we report successful epitaxial growth of metal-rich chalcogenide Fe_(2)Te, a honeycomb-structured film that has no direct bulk analogue, under Te-limited growth conditions. The structural morphology and electronic properties of Fe_(2)Te are explored with scanning tunneling microscopy and angle resolved photoemission spectroscopy, which reveal electronic bands cross the Fermi level and nearly flat bands. Moreover, we find a weak interfacial interaction between Fe_(2)Te and the underlying substrates, paving a newly developed alternative avenue for honeycomb-based electronic devices.

Butterfly-Like Anisotropic Magnetoresistance and Angle-Dependent Berry Phase in a Type-ⅡWeyl Semimetal WP2

The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport studies show a butterfly-like magnetoresistance at low temperature,reflecting the anisotropy of the electron Fermi surfaces.This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature,mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance.Moreover,an angle-dependent Berry phase is also discovered,based on quantum oscillations,which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space.The revealed topological character and anisotropic Fermi surfaces of the WP2 substantially enrich the physical properties of Weyl semimetals,and show great promises in terms of potential topological electronic and Fermitronic device applications.

Band Structures of Ultrathin Bi(110) Films on Black Phosphorus Substrates Using Angle-Resolved Photoemission Spectroscopy

The band structures of two-monolayer Bi（110） films on black phosphorus substrates are studied using angleresolved photoemission spectroscopy. Within the band gap of bulk black phosphorus, the electronic states near the Fermi level are dominated by the Bi（110） film. The band dispersions revealed by our data suggest that the orientation of the Bi（110） film is aligned with the black phosphorus substrate. The electronic structures of the Bi（110） film strongly deviate from the band calculations of the free-standing Bi（110） film, suggesting that the substrate can significantly affect the electronic states in the Bi（110） film. Our data show that there are no non-trivial electronic states in Bi（110） films grown on black phosphorus substrates.