Abstract
We have investigated the valley Chern number and gapless edge states in wide-gap semiconductor SiC and BN monolayers by using the density functional theory calculations. We found that while SiC monolayer has a non-quantized valley Chern number due to a partial mixing of the Berry curvature peaks pertaining to the opposite valleys, there exist topologically protected gapless edge states within the bulk gap, leading to a quantum valley Hall effect. Doping of the opposite charge carriers causes a backscattering-free valley current flowing on the opposite edge, which can be used for experimental confirmation and application at room temperature. BN monolayer, on the other hand, was found to have gapped edge states due to the too large staggered AB-sublattice potentials.
Highlights
We have investigated the valley Chern number and gapless edge states in wide-gap semiconductor SiC and BN monolayers by using the density functional theory calculations
As Δ increases, the Berry curvature peak broadens while maintaining its center at each valley, and the valley Chern number may deviate from the quantized value due to a partial mixing of the Berry curvature peaks pertaining to opposite valleys[15]
The valley-resolved Chern number for the lower boundary phonons of the frequency gap is 0.28ξ, which deviates from the ideal value of 0.5ξ and was attributed to a partial mixing of the Berry curvature peaks pertaining to the opposite valleys[15,18]
Summary
We have investigated the valley Chern number and gapless edge states in wide-gap semiconductor SiC and BN monolayers by using the density functional theory calculations. We found that while SiC monolayer has a non-quantized valley Chern number due to a partial mixing of the Berry curvature peaks pertaining to the opposite valleys, there exist topologically protected gapless edge states within the bulk gap, leading to a quantum valley Hall effect. The non-quantized valley Chern number may result from a partial mixing of the broad Berry curvature peak pertaining to each valley[15,18] and we investigated zigzag-edge SiC nanoribbons in order to determine the corresponding valley Hall effect. To clarify the effect of a large staggered AB-sublattice potential on the valley Chern number and gapless edge states, the TB model of Eq (1) for a 2D honeycomb lattice was investigated. The valley Chern number is not quantized in the diatomic 2D honeycomb monolayers, because the Berry curvature peaks pertaining to opposite valleys are broadened and partially mixed due to large staggered AB-sublattice potentials. BN monolayer has gapped edge states due to the too large staggered AB-sublattice potentials
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