Linear wave dynamics explains observations attributed to dark-solitons in a polariton quantum fluid

We investigate the propagation and scattering of polaritons in a planar GaAs microcavity in the linear regime under resonant excitation. The propagation of the coherent polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons. We demonstrate that these features are observed for negligible nonlinearity (i.e., polariton-polariton interaction) and are, therefore, not sufficient to identify dark and half-dark solitons. A linear model based on the Maxwell equations is shown to reproduce the experimental observations.Comment: Article + Supplementary Information (tot. 18 pages

Magneto-Seebeck microscopy of domain switching in collinear antiferromagnet CuMnAs

Antiferromagnets offer spintronic device characteristics unparalleled in ferromagnets owing to their lack of stray fields, THz spin dynamics, and rich materials landscape. Microscopic imaging of antiferromagnetic domains is one of the key prerequisites for understanding physical principles of the device operation. However, adapting common magnetometry techniques to the dipolar-field-free antiferromagnets has been a major challenge. Here we demonstrate in a collinear antiferromagnet a thermoelectric detection method by combining the magneto-Seebeck effect with local heat gradients generated by scanning far-field or near-field techniques. In a 20-nm epilayer of uniaxial CuMnAs we observe reversible 180∘ switching of the Néel vector via domain wall displacement, controlled by the polarity of the current pulses. We also image polarity-dependent 90∘ switching of the Néel vector in a thicker biaxial film, and domain shattering induced at higher pulse amplitudes. The antiferromagnetic domain maps obtained by our laboratory technique are compared to measurements by the established synchrotron-based technique of x-ray photoemission electron microscopy using x-ray magnetic linear dichroism

Exciton Spin Dynamics in Semiconductor Quantum Wells

In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum Wells. The spin properties of excitons in nanostructures are determined by their fine structure. We will mainly focus in this review on GaAs and InGaAs quantum wells which are model systems.Comment: 55 pages, 27 figure

Light Propogation in Planar Optical Waveguides made of Silicon Nanocrystals Buried in Silica Glass

Silicon nanocrystals fabricated by Si+-ion implantation (400 keV, fluences from 4 to 6 × 1017 cm- 2) of fused silica form interesting active planar optical waveguides. The nanocrystals emit orange-red photoluminescence (PL) (under UV-blue excitation) an

Longitudinal optical phonon assisted polariton laser

We demonstrate the role of longitudinal optical (LO)-phonon assisted polariton relaxation in reducing the stimulation threshold in strongly coupled microcavities. When the energy of the relaxation bottleneck is one LO-phonon above the ground polariton state, we observe a tenfold improvement of the polariton relaxation rate in the linear regime, and a twofold reduction in the threshold to the nonlinear polariton lasing regime.Microcavity polaritons are quasibosons that result from the strong-coupling of cavity photons and excitons confined in a single nanostructure.1 Their bosonic nature gives rise to a plethora of nonlinear phenomena2,3 epitomized by the quantum phase transition to nonequilibrium Bose–Einstein condensation.4–6 The lifetime of polariton condensates is limited to the cavity-photon lifetime leading to the radiation of directional, coherent light, termed polariton laser.7 Unlike conventional lasers, polariton lasers do not require population inversion and have the potential to operate with reduced thresholds. To date, polariton lasers have only been realized under optical excitation in microcavities with GaAs,8 CdTe,9 and GaN (Ref. 10) active material. Although electrical pumping in polariton light emitting diodes was achieved both in inorganic and organic microcavities,11–13 polariton lasing remains elusive under electrical carrier injection. As with nonresonant optical excitation schemes, so with electrical injection relaxation bottleneck leads to substantial homogeneous broadening and loss of strong coupling in the linear regime

Waveguide Cores Containing Silicon Nanocrystals as Active Spectral Filters for Silicon-based Photonics

Layers of densely packed luminescent Si nanocrystals embedded in fused silica act as wavelength-specific planar waveguides that filter the wide-band spontaneous emission. The waveguides' light output consists of two spectrally narrow (∼ 10 nm), orthogo