27,314 research outputs found
Three-Dimensional Topological Insulator in a Magnetic Field: Chiral Side Surface States and Quantized Hall Conductance
Low energy excitation of surface states of a three-dimensional topological
insulator (3DTI) can be described by Dirac fermions. By using a tight-binding
model, the transport properties of the surface states in a uniform magnetic
field is investigated. It is found that chiral surface states parallel to the
magnetic field are responsible to the quantized Hall (QH) conductance
multiplied by the number of Dirac cones. Due to the
two-dimension (2D) nature of the surface states, the robustness of the QH
conductance against impurity scattering is determined by the oddness and
evenness of the Dirac cone number. An experimental setup for transport
measurement is proposed
Identifying (BN)2-pyrene as a new class of singlet fission chromophores: significance of azaborine substitution
Singlet fission converts one photoexcited singlet state to two triplet excited states and raises photoelectric conversion efficiency in photovoltaic devices. However, only a handful of chromophores have been known to undergo this process, which greatly limits the application of singlet fission in photovoltaics. We hereby identify a recently synthesized diazadiborine-pyrene ((BN)2-pyrene) as a singlet fission chromophore. Theoretical calculations indicate that it satisfies the thermodynamics criteria for singlet fission. More importantly, the calculations provide a physical chemistry insight into how the BN substitution makes this happen. Both calculation and transient absorption spectroscopy experiment indicate that the chromophore has a better absorption than pentacene. The convenient synthesis pathway of the (BN)2-pyrene suggests an in situ chromophore generation in photovoltaic devices. Two more (BN)2-pyrene isomers are proposed as singlet fission chromophores. This study sets a step forward in the cross-link of singlet fission and azaborine chemistry
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