Brillouin zone

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

Brillouin Light Scattering by Magnetic Quasivortices in Cavity Optomagnonics.

Abstract: A ferromagnetic sphere can support optical vortices in the form of whispering gallery modes and magnetic quasivortices in the form of magnetostatic modes with nontrivial spin textures. These vortices can be characterized by their orbital angular momenta. We experimentally investigate Brillouin scattering of photons in the whispering gallery modes by magnons in the magnetostatic modes, zeroing in on the exchange of the orbital angular momenta between the optical vortices and magnetic quasivortices. We find that the conservation of the orbital angular momentum results in different nonreciprocal behavior in the Brillouin light scattering. New avenues for chiral optics and optospintronics can be opened up by taking the orbital angular momenta as a new degree of freedom for cavity optomagnonics.

Gapless spin-liquid state in the structurally disorder-free triangular antiferromagnet NaYbO 2

Abstract: We present a candidate material, NaYbO2, that realizes the genuine spin-liquid state on the triangular lattice and benchmarks recent theoretical predictions on the relevant spin models. Synchrotron x-ray diffraction and neutron scattering exclude both structural disorder and crystal-electric-field randomness. Our thermodynamic measurements, neutron diffraction, and muon spectroscopy coincidentally prove the absence of magnetic order and persistent spin dynamics down to at least 70 mK. Continuous magnetic excitations first observed by inelastic neutron scattering show a gapless feature and the low-energy spectral weight accumulating at the K point of the Brillouin zone, in agreement with theoretical predictions for the spin-liquid phase of triangular antiferromagnets. Such a gapless spin-liquid phase is further confirmed by our magnetic specific heat analysis that reveals a departure from simple power-law behavior. Our work demonstrates that NaYbO2 practically gives direct experimental access to the spin-liquid physics of triangular antiferromagnets.

Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals

Abstract: Starting from first principles, we theoretically model the nonlinear temporal dynamics of gold-based plasmonic devices resulting from the heating of their metallic components. At optical frequencies, the gold susceptibility is determined by the interband transitions around the X, L points in the first Brillouin zone, and thermo-modulational effects ensue from Fermi smearing of the electronic energy distribution in the conduction band. As a consequence of light-induced heating of the conduction electrons, the optical susceptibility becomes nonlinear. In this paper we describe, for the first time to our knowledge, the effects of the thermo-modulational nonlinearity of gold on the propagation of surface plasmon polaritons guided on gold nanowires. We introduce a novel nonlinear Schr¨ odinger-like equation to describe pulse propagation in such nanowires, and we predict the appearance of an intense spectral red-shift caused by the delayed thermal response.

Intermediate-band solar cells: Influence of band formation on dynamical processes in InAs/GaAs quantum dot arrays

Abstract: We present a theoretical model for design and analysis of semiconductor quantum dot (QD) array-based intermediate-band solar cell (IBSC). The plane-wave method with periodic boundary conditions is used in expansion of the $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Hamiltonian for calculation of the electronic and optical structures of InAs/GaAs QD array. Taking into account realistic QD shape, QD periodicity in the array, as well as effects such as band mixing between states in the conduction and valence band, strain and piezoelectric field, the model reveals the origin of the intermediate-band formation inside forbidden energy gap of the barrier material. Having established the interrelation between QD periodicity and the electronic structure across the QD array Brillouin zone, conditions are identified for the appearance of pure zero density-of-states regions, that separate intermediate band from the rest of the conduction band. For one realistic QD array we have estimated all important absorption coefficients in IBSC, and most important, radiative and nonradiative scattering times. Under radiative-limit approximation we have estimated efficiency of such IBSC to be 39%.

Valley phonons and exciton complexes in a monolayer semiconductor.

Abstract: The coupling between spin, charge, and lattice degrees of freedom plays an important role in a wide range of fundamental phenomena. Monolayer semiconducting transitional metal dichalcogenides have emerged as an outstanding platform for studying these coupling effects. Here, we report the observation of multiple valley phonons – phonons with momentum vectors pointing to the corners of the hexagonal Brillouin zone – and the resulting exciton complexes in the monolayer semiconductor WSe2. We find that these valley phonons lead to efficient intervalley scattering of quasi particles in both exciton formation and relaxation. This leads to a series of photoluminescence peaks as valley phonon replicas of dark trions. Using identified valley phonons, we also uncover an intervalley exciton near charge neutrality. Our work not only identifies a number of previously unknown 2D excitonic species, but also shows that monolayer WSe2 is a prime candidate for studying interactions between spin, pseudospin, and zone-edge phonons. In monolayer semiconductors phonons with momentum vectors pointing to the corners of the hexagonal Brillouin zone couple strongly to carriers’ spin and valley degree of freedom. Here, the authors report the observation of multiple valley phonons and the resulting exciton complexes in the monolayer semiconductor WSe2.