Several examples of metallic electron doped polycyclic aromatic hydrocarbons (PAHs) molecular crystals have recently been experimentally proposed. Some of them have superconducting components, but most other details are still unknown beginning with structure and the nature of metallicity. We carried out ab-initio density functional calculations for La-Phenanthrene (La-PA), here meant to represent a generic case of three-electron doping, to investigate structure and properties of a conceptually simple case. To our surprise we found first of all that the lowest energy state is not metallic but band insulating, with a disproportionation of two inequivalent PA molecular ions and a low P1 symmetry, questioning the common assumption that three electrons will automatically metallize a PAH crystal. Our best metallic structure is metastable and slightly higher in energy, and retains equivalent PA ions and a higher P21 symmetry -- the same generally claimed for metallic PAHs. We show that a "dimerizing" periodic distortion opens very effectively a gap in place of a symmetry related degeneracy of all P21 structures near the Fermi level, foreshadowing a possible role of that special intermolecular phonon in superconductivity of metallic PAHs. A Hubbard-Frohlich model describing that situation is formulated for future studies.
We study amorphous systems with completely random sites and find that, through constructing and exploring a concrete model Hamiltonian, such a system can host an exotic phase of topological amorphous metal in three dimensions. In contrast to the traditional Weyl semimetals, topological amorphous metals break translational symmetry, and thus they cannot be characterized by the first Chern number defined based on the momentum space band structures. Instead, their topological properties will manifest in the Bott index and the Hall conductivity as well as the surface states. By studying the energy band and quantum transport properties, we find that topological amorphous metals exhibit a diffusive metal behavior. We further introduce a practical experimental proposal with electric circuits where the predicted phenomena can be observed using state-of-the-art technologies. Our results open the door to exploring topological gapless phenomena in amorphous systems.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
We obtain a set of general formulae for determining magnetizations, including the usual electromagnetic magnetization as well as the gravitomagnetic energy magnetization. The magnetization corrections to the thermal transport coefficients are explicitly demonstrated. Our theory provides a systematic approach for properly evaluating the thermal transport coefficients of magnetic systems, eliminating the unphysical divergence from the direct application of the Kubo formula. For an anomalous Hall system, the corrected thermal Hall conductivity obeys the Wiedemann-Franz law.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A novel, to the best of our knowledge, photodetector with a metalens packaging module used as the visible light communication (VLC) receiver is proposed and designed. An LED consisting of red, green, blue, and yellow chips (RGBY-LED) is adopted as the transmitter for intensity modulation direct detection VLC systems. A metalens array with a numerical aperture (NA) of 0.707 used as a polarization-insensitive planar lens of the VLC system receiver is designed at wavelengths of 457, 523, 592, and 623 nm corresponding to blue, green, yellow, and red for high efficiency. Compared with a traditional Fresnel lens positive-intrinsic-negative (PIN) photodetector module as the VLC receiver, the introduction of a metalens module can decrease the form factor of the VLC receiver module and, in particular, it is much thinner. The combination of the multi-color LED transmitter and photodetector metalens packaging module receiver can increase the modulation bandwidth due to four different wavelengths used for the VLC system. Finite-difference time domain (FDTD) simulations are performed to validate the performance of the photodetector with a metalens module. It is revealed that the corresponding efficiencies of 57.5%, 55.4%, 57%, and 56.3% were achieved at wavelengths of 623, 592, 523, and 457 nm, respectively, based on a metalens array with a 0.707 NA and 2.5 µm radius of the active area of the photodetector. It is a promising technology for indoor VLC systems such as those for smart phones and other Internet of Things devices due to the need for compact packaging for the receiver.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
We analyze various possible superconducting pairing states and their relative stabilities in lightly doped graphene.We show that, when inter-sublattice electron-electron attractive interaction dominates and Fermi level is close to Dirac points, the system will favor intra-valley spin-triplet p + ip pairing state.Based on the novel pairing state, we further propose a scheme for doing topological quantum computation in graphene by engineering local strain fields and external magnetic fields.
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