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Université de Fribourg

How circular dichroism in time- and angle-resolved photoemission can be used to spectroscopically detect transient topological states in graphene

Schüler, Michael ; Giovannini, Umberto De ; Hübener, Hannes ; Rubio, Angel ; Sentef, Michael A. ; Devereaux, Thomas P. ; Werner, Philipp

In: Physical Review X, 2020, vol. 10, no. 4, p. 041013

Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern-insulator state and demonstrating clear experimental evidence for its topological nature has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic...

Université de Fribourg

Structural diversity with varying disorder enables the multicolored display in the longhorn beetle Sulawesiella rafaelae

Bermúdez-Ureña, Esteban ; Kilchoer, Cédric ; Lord, Nathan P. ; Steiner, Ullrich ; Wilts, Bodo

In: iScience, 2020, vol. 23, no. 7, p. -

Light control through layered photonic nanostructures enables the strikingly colored displays of many beetles, birds, and butterflies. To achieve different reflected colors, natural organisms mainly rely on refractive index variations or scaling of a fixed structure design, as opposed to varying the type of structure. Here, we describe the presence of distinct coloration mechanisms in the...

Université de Fribourg

Impact of bottom water currents on benthic foraminiferal assemblages in a cold-water coral environment: The Moira Mounds (NE Atlantic)

Fentimen, Robin ; Lim, Aaron ; Rüggeberg, Andres ; Wheeler, Andrew J. ; Rooij, David Van ; Foubert, Anneleen

In: Marine Micropaleontology, 2020, vol. 154, p. 101799

Strong bottom currents play a key role in cold-water coral environments by shaping their morphology and providing the necessary food for the corals to thrive. This study investigates the differences between living and dead benthic foraminiferal assemblages in such environments, more precisely on the Moira Mounds (NE Atlantic). A specific focus is to understand the role of currents and their...

Université de Fribourg

A literal elytral rainbow: tunable structural colors using single diamond biophotonic crystals in Pachyrrhynchus congestus weevils

Wilts, Bodo D. ; Saranathan, Vinodkumar

In: Small, 2018, vol. 14, no. 46, p. 1802328

The brilliant colors of many insects arise from the interference of incident light with complex nanostructured biomaterials that are present in their cuticle. Here, the rainbow‐colored spots on the elytra of a snout weevil, Pachyrrhynchus congestus pavonius (Coleoptera: Curculionidae), are investigated using synchrotron small‐angle X‐ray scattering, scanning electron microscopy,...

Université de Fribourg

Terahertz vortex beam as a spectroscopic probe of magnetic excitations

Sirenko, Andrei A. ; Maršík, Premysl ; Bernhard, Christian ; Stanislavchuk, T. N. ; Kiryukhin, V. ; Cheong, S.-W.

In: Physical Review Letters, 2019, vol. 122, no. 23, p. 237401

Circularly polarized light with spin angular momentum is one of the most valuable probes of magnetism. We demonstrate that light beams with orbital angular momentum (OAM), or vortex beams, can also couple to magnetism exhibiting dichroisms in a magnetized medium. Resonant optical absorption in a ferrimagnetic crystal depends strongly on both the handedness of the vortex and the direction of...

Université de Fribourg

The structural colors of photonic glasses

Schertel, Lukas ; Siedentop, Lukas ; Meijer, Janne-Mieke ; Keim, Peter ; Aegerter, Christof M. ; Aubry, Geoffroy J. ; Maret, Georg

In: Advanced Optical Materials, 2019, p. 1900442

The color of materials usually originates from a combination of wavelength‐dependent absorption and scattering. Controlling the color without the use of absorbing dyes is of practical interest, not only because of undesired bleaching properties of dyes but also regarding minimization of environmental and health issues. Color control without dyes can be achieved by tuning the material's...

Université de Fribourg

Benthic foraminifera in a deep-sea high-energy environment: the Moira Mounds (Porcupine Seabight, SW of Ireland)

Fentimen, Robin ; Rüggeberg, Andres ; Lim, Aaron ; El Kateb, Akram ; Foubert, Anneleen ; Wheeler, Andrew J. ; Spezzaferri, Silvia

In: Swiss Journal of Geosciences, 2018, vol. 111, no. 3, p. 561–572

Cold-water coral ecosystems represent unique and exceptionally diverse environments in the deep-sea. They are well developed along the Irish margin, varying broadly in shape and size. The Moira Mounds, numerous small-sized mounds, are nestled in the Belgica Mound Province (Porcupine Seabight, North-East Atlantic). The investigation of living (Rose Bengal stained) and dead benthic...

Université de Fribourg

Circularly polarized reflection from the scarab beetle Chalcothea smaragdina: light scattering by a dual photonic structure

McDonald, Luke T. ; Finlayson, Ewan D. ; Wilts, Bodo D. ; Vukusic, Pete

In: Interface Focus, 2017, vol. 7, no. 4, p. 20160129

Helicoidal architectures comprising various polysaccharides, such as chitin and cellulose, have been reported in biological systems. In some cases, these architectures exhibit stunning optical properties analogous to ordered cholesteric liquid crystal phases. In this work, we characterize the circularly polarized reflectance and optical scattering from the cuticle of the beetle Chalcothea...