Brillouin zone

About: Brillouin zone is a research topic. Over the lifetime, 13849 publications have been published within this topic receiving 383077 citations.

Parametric Instabilities in Bounded Plasmas

Abstract: We have obtained conditions for excitation of parametric instabilities in bounded plasmas. Damping and inhomogeneity effects are taken into account. The results are found to be of special importance for backscatter Brillouin instability.

Advanced thermoelectrics governed by a single parabolic band: Mg2Si0.3Sn0.7, a canonical example

Abstract: The well-known single parabolic band (SPB) model has been useful in providing insights into the understanding of transport properties of numerous thermoelectric materials. However, the conduction and valence bands of real semiconductors are rarely truly parabolic which limits the predictive power of the SPB model. The coincidence of the band edges of two parabolic bands, a situation arising in Mg2Si1−xSnx solid solutions when x ∼ 0.7, naturally makes the SPB approximation applicable to evaluate all transport parameters. We demonstrate this in the case of Bi-doped Mg2Si0.3Sn0.7 where the minima of the two conduction bands at the X-point of the Brillouin zone coincide. The combination of a large density-of-states effective mass m* ∼ 2.6 me arising from the enhanced valley degeneracy Nv, high mobility μd due to low deformation potential Ed (8.77–9.43 eV), and ultra-low alloy scattering parameter Ea (0.32–0.39 eV) leads to an outstanding power factor, PFmax ∝ (m*)3/2μd, of up to 4.7 mW m−1 K−2 at around 600 K. The specification and improved understanding of scattering parameters using the SPB model are important and instructive for further optimization of the thermoelectric performance of n-type Mg2Si0.3Sn0.7.

Topological node-line semimetal in compressed black phosphorus

Abstract: Based on first-principles calculations and tight-binding model analysis, we propose that black phosphorus (BP) can host a three-dimensional topological node-line semimetal state under pressure when spin-orbit coupling (SOC) is ignored. A closed topological node line exists in the first Brillouin zone (BZ) near the Fermi energy, which is protected by the coexistence of time-reversal and spatial inversion symmetry with band inversion driven by pressure. Drumheadlike surface states have been obtained on the beard (100) surface. Due to the weak intrinsic SOC of a phosphorus atom, a band gap less than 10 meV is opened along the node line in the presence of SOC, and the surface states are almost unaffected by SOC.

Dirac cone in two- and three-dimensional metamaterials.

Abstract: It is shown by analytical calculation based on the tight-binding approximation that the isotropic Dirac cone in the Brillouin zone center can be created in two- and three-dimensional periodic metamaterials by accidental degeneracy of two modes. In the case of two dimensions, the combination of a doubly degenerate E mode and a non-degenerate A1 mode of the square lattice of the C4v symmetry is examined. For three dimensions, the combination of a triply degenerate T1u mode and a non-degenerate A1g mode of the cubic lattice of the Oh symmetry is examined. The secular equation of the electromagnetic field is derived and solved with detailed analysis of electromagnetic transfer integrals by group theory. This is the first theoretical prediction of the presence of the Dirac cone in the three-dimensional periodic structure.

Orbital-selective Dirac fermions and extremely flat bands in frustrated kagome-lattice metal CoSn

Abstract: Layered kagome-lattice 3d transition metals are emerging as an exciting platform to explore the frustrated lattice geometry and quantum topology. However, the typical kagome electronic bands, characterized by sets of the Dirac-like band capped by a phase-destructive flat band, have not been clearly observed, and their orbital physics are even less well investigated. Here, we present close-to-textbook kagome bands with orbital differentiation physics in CoSn, which can be well described by a minimal tight-binding model with single-orbital hopping in Co kagome lattice. The capping flat bands with bandwidth less than 0.2 eV run through the whole Brillouin zone, especially the bandwidth of the flat band of out-of-plane orbitals is less than 0.02 eV along Γ−M. The energy gap induced by spin-orbit interaction at the Dirac cone of out-of-plane orbitals is much smaller than that of in-plane orbitals, suggesting orbital-selective character of the Dirac fermions. The understanding of kagome bands, which are characterized by Dirac-like bands capped by a flat band, remains largely elusive. Here, Liu et al. report the observation of a flat band and Dirac bands as ideal features of kagome bands in CoSn, revealing orbital-selective character.