Search results for "Physics::Optics"
showing 10 items of 1958 documents
Infrared plasmons propagate through a hyperbolic nodal metal
2022
Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. A special form of optical waveguiding is afforded by highly anisotropic crystals revealing the opposite signs of the dielectric functions along orthogonal directions. These media are classified as hyperbolic and include crystalline insulators, semiconductors, and artificial metamaterials. Layered anisotropic metals are also anticipated to support hyperbolic waveguiding. However, this behavior remains elusive, primarily because interband losses arrest the propagation of infrared modes. Here, we report on the observation of propagating hyperbolic waves in a pr…
Probing phonon dynamics with multidimensional high harmonic carrier-envelope-phase spectroscopy
2022
We explore pump-probe high harmonic generation (HHG) from monolayer hexagonal-Boron-Nitride, where a terahertz pump excites coherent optical phonons that are subsequently probed by an intense infrared pulse that drives HHG. We find, through state-of-the-art ab-initio calculations, that the structure of the emission spectrum is attenuated by the presence of coherent phonons, and is no longer comprised of discrete harmonic orders, but rather of a continuous emission in the plateau region. The HHG yield strongly oscillates as a function of the pump-probe delay, corresponding to ultrafast changes in the lattice such as bond compression or stretching. We further show that in the regime where the…
Inelastic neutron scattering due to acoustic vibrations confined in nanoparticles: theory and experiment
2008
The inelastic scattering of neutrons by nanoparticles due to acoustic vibrational modes (energy below 10 meV) confined in nanoparticles is calculated using the Zemach-Glauber formalism. Such vibrational modes are commonly observed by light scattering techniques (Brillouin or low-frequency Raman scattering). We also report high resolution inelastic neutron scattering measurements for anatase TiO2 nanoparticles in a loose powder. Factors enabling the observation of such vibrations are discussed. These include a narrow nanoparticle size distribution which minimizes inhomogeneous broadening of the spectrum and the presence of hydrogen atoms oscillating with the nanoparticle surfaces which enhan…
Control of transport phenomena in magnetic heterostructures by wavelength modulation
2021
We demonstrate the tuneablity of the ultrafast energy flow in magnetic/non-magnetic bilayer structures by changing the wavelength of the optical excitation. This is achieved by an advanced description of the temperature based $\mu$T-model that explicitly considers the wavelength- and layer-dependent absorption profile within multilayer structures. For the exemplary case of a Ni/Au bilayer, our simulations predict that the energy flow from Ni to Au is reversed when changing the wavelength of the excitation from the infrared to the ultraviolet spectral range. These predictions are fully supported by characteristic signatures in the magneto-optical Kerr traces of the Ni/Au model system. Our re…
Polarization-dependent excitons and plasmon activity in nodal-line semimetal ZrSiS
2022
The optical properties of bulk ZrSiS nodal-line semimetal are theoretically studied within a many-body formalism. The G0W0 bands are similar to those calculated within the density functional theory, except near the {\Gamma} point; in particular, no significant differences are found around the Fermi energy. On the other hand, the solution of the Bethe-Salpeter equation reveals a significant excitonic activity, mostly as dark excitons which appear in a wide energy range. Bright excitons, on the contrary, are less numerous, but their location and intensity depend greatly on the polarization of the incident electric field, as the absorption coefficient itself does. The binding energy of these e…
Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin-phonon interactions
2022
Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modelling, two excitation processes of magnetization dynamics in NiO, an off-resonant instantaneous optical spin torque and a strain-wave-induced THz torque induced by ultrafast Pt excitatio…
Maxwell's equations approach to soliton excitations of surface plasmonic resonances
2012
We demonstrate that soliton-plasmon bound states appear naturally as propagating eigenmodes of nonlinear Maxwell's equations for a metal/dielectric/Kerr interface. By means of a variational method, we give an explicit and simplified expression for the full-vector nonlinear operator of the system. Soliplasmon states (propagating surface soliton-plasmon modes) can be then analytically calculated as eigenmodes of this non-selfadjoint operator. The theoretical treatment of the system predicts the key features of the stationary solutions and gives physical insight to understand the inherent stability and dynamics observed by means of finite element numerical modeling of the time independent nonl…
Quantum paraelectric behavior of pyrochlore PMN
2007
Pb_1.83Mg_0.29Nb_1.71O_6.39 (PMN) crystallizing in a cubic pyrochlore structure exhibits, as the first dielectrics with pyrochlore structure, typical feature of quantum paraelectrics - its permittivity continuously increases on cooling and levels off below ~ 30K, without any signature of a structural phase transition. Broad-band dielectric spectra do not show any dielectric dispersion in the real part of permittivity up to 8.8 GHz. THz and infrared spectra reveal a soft polar optic mode which is responsible for the temperature dependence of the permittivity. The leveling-off of the permittivity at low temperatures obeys the Barrett formula and the fitted vibrational zero-point energy 1/(2*k…
Out-of-plane orientation of luminescent excitons in atomically thin indium selenide flakes
2019
Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe$_2$ and MoSe$_2$. We demonstrate, with the support of ab-initio calculations, that layered InSe flakes sustain luminescent excitons with an intrinsic out-of-plane orientation, in contrast with the in-plane orientation of dipoles we find in two-dimensional WSe$_2$ and MoSe$…
Диссипативное туннелирование электронов в вертикально связанных двойных асимметричных квантовых точках InAs/GaAs(001)
2021
We report on the results of experimental studies of the photoelectric properties of a GaAs p-i-n photodiode with InAs/GaAs(001) double asymmetric quantum dots (DAQDs) grown by self-assembling in Metal Organic Vapor Phase Epitaxy (MOVPE) process. Three peaks were observed in the dependence of the photocurrent on the reverse bias measured at monochromatic photoexcitation of the DAQDs at the wavelength corresponding to the energy of interband optical transitions between the ground hole and electron states in the bigger QDs. These peaks were related to the tunneling of the photoexcited electrons between the QDs including the dissipative one (with emission and absorption of the optical phonons)…