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Université de Fribourg

Revealing Hund’s multiplets in Mott insulators under strong electric fields

Dasari, Nagamalleswararao ; Li, Jiajun ; Werner, Philipp ; Eckstein, Martin

In: Physical Review B, 2020, vol. 101, no. 16, p. 161107

We investigate the strong-field dynamics of a paramagnetic two-band Mott insulator using real-time dynamical mean-field theory. We demonstrate that strong electric fields can lead to a transient localization of electrons. This nonequilibrium quantum effect allows us to reveal specific signatures of local correlations in the time-resolved photoemission spectrum. In particular, we demonstrate...

Université de Fribourg

Photoenhanced excitonic correlations in a Mott insulator with nonlocal interactions

Bittner, Nikolaj ; Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2020, vol. 101, no. 8, p. 085127

We investigate the effect of nonlocal interactions on the photodoped Mott insulating state of the two-dimensional Hubbard model using a nonequilibrium generalization of the dynamical cluster approximation. In particular, we compare the situation where the excitonic states are lying within the continuum of doublon-holon excitations to a setup where the excitons appear within the Mott gap. In...

Université de Fribourg

Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials

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

In: Science Advances, 2020, vol. 6, no. 9, p. eaay2730

Topologically nontrivial two-dimensional materials hold great promise for next- generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular...

Université de Fribourg

Imaging magnetic nanoparticle distributions by atomic magnetometry-based susceptometry

Colombo, Simone ; Lebedev, Victor ; Tonyushkin, Alexey ; Pengue, Simone ; Weis, Antoine

In: IEEE Transactions on Medical Imaging, 2020, vol. 39, no. 4, p. 922–933

We introduce a Magnetic Particle Imaging Susceptometer (MPIS) that uses a high- sensitivity atomic magnetometer (AM) for recording the spatial distribution of fluid- suspended magnetic nanoparticles. We have evaluated the MPIS performance by one-dimensional scans of structured nanoparticle phantoms, demonstrating, in particular, resolutions of ≈2.5 mm prior to deconvolution and ≪1 mm after ...

Université de Fribourg

Variations of the Herschel–Bulkley exponent reflecting contributions of the viscous continuous phase to the shear rate-dependent stress of soft glassy materials

Caggioni, Marco ; Trappe, Veronique ; Spicer, Patrick T.

In: Journal of Rheology, 2020, vol. 64, no. 2, p. 413–422

We explore the flow behavior of concentrated emulsions for which the viscosity of the continuous phase can be significantly varied by changing the temperature. The exponents obtained by fitting the shear rate-dependent stress with the popular Herschel–Bulkley (HB) model display a systematic dependence on the viscosity of the continuous phase, revealing that viscous dissipation via the...

Université de Fribourg

Colloidal gelation, a means to study elasto-capillarity effects in foam

Mikhailovskaya, Alesya ; Trappe, Véronique ; Salonen, Anniina

In: Soft Matter, 2020, vol. 16, no. 9, p. 2249–2255

We explore the evolution of the mechanical properties of a coarsening foam containing colloidal particles that undergo a sol–gel transition in the continuous phase. This enables us to investigate the impact of elasto-capillarity on foam mechanics over a wide range of elasto-capillary numbers. Right after initiating aggregation the foam mechanics is predominantly determined by the elasticity...

Université de Fribourg

Backfolded acoustic phonons as ultrasonic probes in metal-oxide superlattices

Lyzwa, F. ; Chan, A. ; Khmaladze, Jarji ; Fürsich, K. ; Keimer, B. ; Bernhard, Christian ; Minola, M. ; Mallett, Benjamin P. P.

In: Physical Review Materials, 2020, vol. 4, no. 4, p. 043606

Ultrasonics have been an incisive probe of internal interfaces in a wide variety of systems ranging from stars to solids. For thin-film structures, however, ultrasound is largely ineffective because the signal is dominated by the substrate. Using confocal Raman spectromicroscopy, we show that multiple reflection of sound waves at internal interfaces of a metal-oxide superlattice generates...

Haute Ecole pédagogique Fribourg

Introduction Évaluation et numérique : des pratiques éclectiques qui explorent des espaces à déchiffrer

Coen, Pierre-François ; Detroz, Pascal ; Younès, Nathalie

In: Évaluer. Journal international de recherche en éducation et formation, 2020, vol. 5, no. 3, p. 1-8

Comment la déferlante numérique qui bouleverse depuis quelques années le monde de l’éducation transforme-t-elle le domaine de l’évaluation ? C’est cette question qui a motivé, lors du colloque de l’ADMEE 2018, les trois coordinateur.trice.s de ce numéro spécial à proposer un symposium intitulé « Evaluation et technologies numériques : quels développements futurs pour quelles...

Haute Ecole pédagogique Fribourg

Corporate Cosmopolitanism: Making an Asset of Diversity and Mobility at Swiss International Schools

Rey, Jeanne ; Bolay, Matthieu

In: ACME: An International Journal for Critical Geographies, 2020, vol. 19, no. 1, p. 106-130

This article explores the subjective spatial relations that international schools in Switzerland seek to produce within the cosmopolitan enclaves they form. Based on ethnographic fieldwork at 21 international schools in Switzerland, we scrutinize practices related to diversity and mobility, which international schools construe as the main vehicles leading to the desired attributes of...

Haute Ecole pédagogique Fribourg

Généalogie de l’‘élève cosmopolite’ et marchandisation de l’‘international’ dans des établissements scolaires privés en Suisse

Rey, Jeanne ; Bolay, Matthieu ; Schubiger, Elisabeth

Ce texte interroge les contextes et modalités du recours à la catégorie de l’‘international’ par des écoles privées en Suisse. À partir d’observations ethnographiques et de référence à des travaux historiographiques, nous dégageons l’hypothèse de trois modalités d’agencement institutionnel de l’‘international‘ dans ces établissements, renvoyant à des modes de...