35 research outputs found
Dirac Fermions in Antiferromagnetic FeSn Kagome Lattices with Combined Space Inversion and Time Reversal Symmetry
Symmetry principles play a critical role in formulating the fundamental laws
of nature, with a large number of symmetry-protected topological states
identified in recent studies of quantum materials. As compelling examples,
massless Dirac fermions are jointly protected by the space inversion symmetry
and time reversal symmetry supplemented by additional crystalline
symmetry, while evolving into Weyl fermions when either or is broken.
Here, based on first-principles calculations, we reveal that massless Dirac
fermions are present in a layered FeSn crystal containing antiferromagnetically
coupled ferromagnetic Fe kagome layers, where each of the and
symmetries is individually broken but the combined symmetry is preserved.
These stable Dirac fermions protected by the combined symmetry with
additional non-symmorphic symmetry can be transformed to either
massless/massive Weyl or massive Dirac fermions by breaking the or
symmetry. Our angle-resolved photoemission spectroscopy
experiments indeed observed the Dirac states in the bulk and two-dimensional
Weyl-like states at the surface. The present study substantially enriches our
fundamental understanding of the intricate connections between symmetries and
topologies of matter, especially with the spin degree of freedom playing a
vital role.Comment: 6 pages, 4 figure
Direct transformation of-alkane into all-conjugated polyene via cascade dehydrogenation
Selective C(sp) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of an on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints, which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring