Brillouin zone

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

Thermodynamics of hexagonal-close-packed iron under Earth’s core conditions

Abstract: The free energy and other thermodynamic properties of hexagonal-close-packed iron are calculated by direct ab initio methods over a wide range of pressures and temperatures relevant to the Earth’s core. The ab initio calculations are based on density-functional theory in the generalized-gradient approximation, and are performed using the projector augmented wave approach. Thermal excitation of electrons is fully included. The Helmholtz free energy consists of three parts, associated with the rigid perfect lattice, harmonic lattice vibrations, and anharmonic contributions, and the technical problems of calculating these parts to high precision are investigated. The harmonic part is obtained by computing the phonon frequencies over the entire Brillouin zone, and by summation of the free-energy contributions associated with the phonon modes. The anharmonic part is computed by the technique of thermodynamic integration using carefully designed reference systems. Detailed results are presented for the pressure, specific heat, bulk modulus, expansion coefficient and Gruneisen parameter, and comparisons are made with values obtained from diamond-anvil-cell and shock experiments.

Electronic Band Structure of TiC, TiN, and TiO

Abstract: The band structure of metallic face-centered cubic TiC, TiN, and TiO has been obtained by the augmented-plane-wave (APW) method at the equivalent of 256 points in the Brillouin zone and for an energy range appropriate to cover the nonmetal $2s$ and $2p$ and the titanium $3d$ and $4s$ states. A density of states, the Fermi energy, and contours of constant energy were obtained for the three compounds. A charge distribution in the APW scheme was derived from the equivalent of 32 points in the zone, and the admixture of the bands was analyzed. The results are consistent with the available experimental data.

Distributed strain measurement with millimeter-order spatial resolution based on Brillouin optical correlation domain analysis

Abstract: Distributed strain sensing with millimeter-order spatial resolution is demonstrated in optical fibers based on Brillouin optical correlation domain analysis. A novel beat lock-in detection scheme is introduced to suppress background noises coming from the reflection of Brillouin pump waves. The Brillouin frequency shifts of 3 mm fiber sections are successfully measured with a theoretical spatial resolution of 1.6 mm.

Observation of a d-wave gap in electron-doped Sr2IrO4

Abstract: Sr2IrO4 bears a striking electronic resemblance to the cuprate superconductors, except the iridate is an insulator. Introducing electrons into Sr2IrO4 leads to a d-wave gap, suggesting superconductivity or something equally exotic. High-temperature superconductivity in cuprates emerges out of a highly enigmatic ‘pseudogap’ metal phase. The mechanism of high-temperature superconductivity is probably encrypted in the elusive relationship between the two phases, which spectroscopically is manifested as Fermi arcs—disconnected segments of zero-energy states—collapsing into d-wave point nodes upon entering the superconducting phase. Here, we reproduce this distinct cuprate phenomenology in the 5d transition-metal oxide Sr2IrO4. Using angle-resolved photoemission, we show that the clean, low-temperature phase of 6–8% electron-doped Sr2IrO4 has gapless excitations only at four isolated points in the Brillouin zone, with a predominant d-wave symmetry of the gap. Our work thus establishes a connection between the low-temperature d-wave instability and the previously reported high-temperature Fermi arcs in electron-doped Sr2IrO4 (ref. 1). Although the physical origin of the d-wave gap remains to be understood, Sr2IrO4 is the first non-cuprate material to spectroscopically reproduce the complete phenomenology of the cuprates, thus offering a new material platform to investigate the relationship between the pseudogap and the d-wave gap.

Honeycomb lattice potentials and Dirac points

Abstract: We prove that the two-dimensional Schroedinger operator with a potential having the symmetry of a honeycomb structure has dispersion surfaces with conical singularities (Dirac points) at the vertices of its Brillouin zone. No assumptions are made on the size of the potential. We then prove the robustness of such conical singularities to a restrictive class of perturbations, which break the honeycomb lattice symmetry. General small perturbations of potentials with Dirac points do not have Dirac points; their dispersion surfaces are smooth. The presence of Dirac points in honeycomb structures is associated with many novel electronic and optical properties of materials such as graphene.