Brillouin zone

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

Chapter 2 Effects of Homogeneous Strain on the Electronic and Vibrational Levels in Semiconductors

Abstract: Publisher Summary This chapter describes the effects of homogeneous strain on the electronic and vibrational levels in semiconductors. It reviews the effects of homogeneous strains on the electronic states of the highest valence and lowest conduction bands of diamond- and zincblende-type materials, focusing on the band extrema at the center of the Brillouin zone (BZ). Electronic deformation potentials for a number of relevant bands are summarized in the chapter. The effects of an external stress on the quantum levels of quantum wells and the properties of strained-layer superlattices with built-in strain are discussed in the chapter. The influence of a homogeneous strain on the optic phonons at the BZ center of certain materials is described and also for this situation, vibrational deformation potentials are listed in the chapter. The introduction of a homogeneous strain in a solid produces changes in the lattice parameter and, in some cases, in the symmetry of the material. These in turn produce significant changes in the electronic band structure and vibrational modes. All configurations of homogeneous strain can be divided into the following two contributions: the isotropic or hydrostatic components, which give rise to a volume change without disturbing the crystal symmetry, and the anisotropic component, which in general reduces the symmetry present in the strain-free lattice.

Pressure-induced topological phase transitions in rocksalt chalcogenides

Abstract: By means of a comprehensive theoretical investigation, we show that external pressure can induce topological phase transitions in IV--VI semiconducting chalcogenides with a rocksalt structure. These materials satisfy mirror symmetries that are needed to sustain topologically protected surface states, at variance with time-reversal symmetry that is responsible for gapless edge states in ${\mathcal{Z}}_{2}$ topological insulators. The band inversions at high-symmetry points in the Brillouin zone that are related by mirror symmetry are brought about by an ``asymmetric'' hybridization between cation and anion $sp$ orbitals. By working out the microscopic conditions to be fulfilled in order to maximize this hybridization, we identify materials in the rocksalt chalcogenide class that are prone to undergo a topological phase transition induced by pressure and/or alloying. Our model analysis is fully confirmed by complementary advanced first-principles calculations and ab initio-based tight-binding simulations.

High-Spin Polaron in Lightly Doped CuO 2 Planes

Abstract: We derive and investigate numerically a minimal yet detailed spin-polaron model that describes lightly doped CuO2 layers. The low-energy physics of a hole is studied by total-spin-resolved exact diagonalization on clusters of up to 32 CuO2 unit cells, revealing features missed by previous studies. In particular, spin-polaron states with total spin 3/2 are the lowest eigenstates in some regions of the Brillouin zone. In these regions, and also at other points, the quasiparticle weight is identically zero indicating orthogonal states to those represented in the one electron Green's function. This highlights the importance of the proper treatment of spin fluctuations in the many-body background.

Bragg diffraction of spin waves from a two-dimensional antidot lattice

Abstract: The spin-wave band structure of a two-dimensional square array of NiFe circular antidots (hole diameter 120 nm, periodicity 800 nm) is investigated. Brillouin light scattering experiments and band structure calculations, carried out by means of the dynamical matrix method, provide evidence for either extended or localized magnonic modes. Both families exhibit band gaps at Brillouin zone boundaries, attributed to Bragg reflection. Their calculated magnitude agrees with the one obtained by using an analytical model that takes into account the periodic variation of the internal field. This is in contrast to antidots in photonics and electronics, where the back-reflection is directly caused by the presence of holes. The results are important for advancing research on nanostructured two-dimensional magnonic crystals.