108 research outputs found
Bilayer Kagome Borophene with Multiple van Hove Singularities
The appearance of van Hove singularities near the Fermi level leads to
prominent phenomena, including superconductivity, charge density wave, and
ferromagnetism. Here a bilayer Kagome lattice with multiple van Hove
singularities is designed and a novel borophene with such lattice
(BK-borophene) is proposed by the first-principles calculations. BK-borophene,
which is formed via three-center two-electron (3c-2e) sigma-type bonds, is
predicted to be energetically, dynamically, thermodynamically, and mechanically
stable. The electronic structure hosts both conventional and high-order van
Hove singularities in one band. The conventional van Hove singularity resulting
from the horse saddle is 0.065 eV lower than the Fermi level, while the
high-order one resulting from the monkey saddle is 0.385 eV below the Fermi
level. Both the singularities lead to the divergence of electronic density of
states. Besides, the high-order singularity is just intersected to a Dirac-like
cone, where the Fermi velocity can reach 1340000 m/s. The interaction between
the two Kagome lattices is critical for the appearance of high-order van Hove
singularities. The novel bilayer Kagome borophene with rich and intriguing
electronic structure offers an unprecedented platform for studying correlation
phenomena in quantum material systems and beyond
Controllable optical and magneto-optical properties of magnetic CrI3 nanoribbons
A monolayer of CrI3 has an amazing ferromagnetic ground-state. In this work,
we calculate band structures and magnetic moments of tensile-strained and bent
zigzag CrI3 nanoribbons with density functional theory. The edge iodine atoms
form flat low-lying conduction bands and couple with chromium atoms
ferromagnetically, while the non-edge iodine atoms weakly couple
antiferromagnetically. CrI3 nanoribbons have a nearly equal preference for the
out-of-plane and in-plane magnetic moment configurations, slightly favoring the
in-plane one. We also calculate optical absorption with many-body perturbation
GW-BSE (Bethe-Salpeter equation) and investigate magneto-optical properties,
including magnetic dichroism, Faraday and magneto-optical Kerr effects. The
low-energy dark excitons are mainly from transitions between electrons and
holes with unlike spins and are non-Frenkel-like, while the bright excitons
have mixed spin configurations. Tensile strains and bending manifestly modulate
the absorption spectra and magneto-optical properties of CrI3 nanoribbons
within a technologically important photon energy-range of ~1.0-2.0 eV,
suggesting a potential application in tunable magnetic optoelectronics.Comment: 17 pages, 5 figure
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