Brillouin zone

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

Sensitivity of the superconducting state and magnetic susceptibility to key aspects of electronic structure in ferropnictides

Abstract: Experiments on the iron–pnictide superconductors appear to show some materials where the ground state is fully gapped, and others where low-energy excitations dominate, possibly indicative of gap nodes. Within the framework of a five-orbital spin fluctuation theory for these systems, we discuss how changes in the doping, the electronic structure or interaction parameters can tune the system from a fully gapped to a nodal sign-changing gap with s-wave (A1g) symmetry (s±). In particular, we focus on the role of the hole pocket at the (π, π) point of the unfolded Brillouin zone, identified as crucial to the pairing by Kuroki et al (2009 Phys. Rev. B 79 224511), and show that its presence leads to additional nesting of hole and electron pockets, which stabilizes the isotropic s± state. The pocket's contribution to the pairing can be tuned by doping, surface effects and by changes in interaction parameters, which we examine. Analytic expressions for orbital pairing vertices calculated within the random phase approximation (RPA) fluctuation exchange approximation allow us to draw connections between aspects of the electronic structure, interaction parameters and the form of the superconducting gap.

Amplification of ultrashort laser pulses by brillouin backscattering in plasmas.

Abstract: Plasma media, by exciting Raman (electron) or Brillouin (ion) waves, have been used to transfer energy from moderately long, high-energy light pulses to short ones. Using multidimensional kinetic simulations, we define here the optimum window in which a Brillouin scheme can be exploited for amplification and compression of short laser pulses over short distances to very high power. We also show that shaping the plasma allows for increasing the efficiency of the process while minimizing other unwanted plasma processes. Moreover, we show that, contrary to what was traditionally thought (i.e., using Brillouin in gases for nanosecond pulse compression), this scheme is able to amplify pulses of extremely short duration.

Tight-Binding Calculation of 3 d Bands of Fe with and without Spin-Orbit Coupling

Abstract: The electronic structure of the $3d$ band in Fe is calculated in the tight-binding approximation; the energy values in the Brillouin zone and the density-of-states curve are evaluated. A comparison with other theoretical results suggests that the approximations and hypotheses used do not influence the results markedly; a comparison with the results previously obtained with the same method for Cr does not support the rigid-band hypothesis. The spin-orbit interaction matrix is reported for a general direction of magnetization, and the effect of spin-orbit coupling on the structure of bcc transition metals is investigated.

Photoinduced possible superconducting state with long-lived disproportionate band filling in FeSe

Abstract: Photoexcitation is a very powerful way to instantaneously drive a material into a novel quantum state without any fabrication, and variable ultrafast techniques have been developed to observe how electron, lattice, and spin degrees of freedom change. One of the most spectacular phenomena is photoinduced superconductivity, and it has been suggested in cuprates that the transition temperature Tc can be enhanced from the original Tc with significant lattice modulations. Here, we show a possibility for another photoinduced high-Tc superconducting state in the iron-based superconductor FeSe. The transient electronic state over the entire Brillouin zone is directly observed by time- and angle-resolved photoemission spectroscopy using extreme ultraviolet pulses obtained from high harmonic generation. Our results of dynamical behaviors from 50 fs to 800 ps consistently support the favourable superconducting state after photoexcitation well above Tc. This finding demonstrates that multiband iron-based superconductors emerge as an alternative candidate for photoinduced superconductors. Light-matter interactions can be used to induce a superconducting-like state in some cuprate superconductors at temperatures above the expected transition temperature. Here, the authors provide time and angle resolved spectroscopic evidence to suggest that photo induced superconductivity can also be achieved in Fe-based superconductors

Accuracy limitations on Brillouin lidar measurements of temperature and sound speed in the ocean.

Abstract: There are five mutually dependent variables relevant to Brillouin lidar measurements of temperature and sound speed in the ocean; they are (1) the Brillouin shift, (2) the sound speed, (3) the index of refraction, (4) the temperature, and (5) the salinity. We use three well-known relations to analyze rigorously the interdependence of these five variables. Clearly, a Brillouin shift measurement does not provide a stand-alone determination of temperature or sound speed; one more variable or one more relation must be known. The use of mean values of salinity that have been obtained by an analysis of a large set of historical in situ data is considered for this additional relation.