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Université de Fribourg

Adjusted oscillator strength matching for hybrid magnetic and electric excitations in Dy₃Fe₅O₁₂ garnet

Rogers, P. D. ; Choi, Y. J. ; Standard, E. C. ; Kang, T. D. ; Ahn, K. H. ; Dubroka, Adam ; Marsik, Premysl ; Wang, Ch. ; Bernhard, Christian ; Park, S. ; Cheong, S.-W. ; Kotelyanskii, M. ; Sirenko, Andrei A.

In: Physical Review B - Condensed Matter and Materials Physics, 2011, vol. 83, no. 17, p. 174407

Far-infrared spectra of magnetodielectric Dy₃Fe₅O₁₂ garnet were studied using a combination of transmittance, reflectivity, and rotating analyzer ellipsometry. In addition to purely dielectric and magnetic modes, we observed several hybrid modes with a mixed magnetic and electric dipole activity. Using 4×4 matrix formalism for materials with μ(ω)≠1, we modeled the experimental...

Université de Fribourg

Anisotropy of infrared-active phonon modes in the monodomain state of tetragonal ${\mathrm{SrTiO}}_{3}$ (110)

Yazdi-Rizi, Meghdad ; Maršík, Premysl ; Mallett, Benjamin P. P. ; Bernhard, Christian

In: Physical Review B, 2017, vol. 95, no. 2, p. 024105

With infrared (IR) and terahertz (THz) ellipsometry we investigated the anisotropy of the IR-active phonon modes in ${\mathrm{SrTiO}}_{3}$ (110) single crystals in the tetragonal state below the so-called antiferrodistortive transition at T∗=105 K. In particular, we show that the anisotropy of the oscillator strength of the so-called R mode, which becomes weakly IR active below T∗, is a...

Université de Fribourg

Anomalous anisotropic exciton temperature dependence in rutile ${\mathrm{TiO}}_{2}$

Baldini, Edoardo ; Dominguez, Adriel ; Chiodo, Letizia ; Sheveleva, Evgeniia ; Yazdi-Rizi, Meghdad ; Bernhard, Christian ; Rubio, Angel ; Chergui, and Majed

In: Physical Review B, 2017, vol. 96, no. 4, p. 041204

Elucidating the details of electron-phonon coupling in semiconductors and insulators is a topic of pivotal interest, as it governs the transport mechanisms and is responsible for various phenomena such as spectral-weight transfers to phonon sidebands and self-trapping. Here, we investigate the influence of the electron-phonon interaction on the excitonic peaks of rutile TiO2, revealing a strong...

Université de Fribourg

Atomic-resolution studies of epitaxial strain release mechanisms in $\mathrm{L}{\mathrm{a}}_{1.85}\mathrm{S}{\mathrm{r}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4}/\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{C}{\mathrm{a}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ superlattices

Biškup, N. ; Das, Saikat ; Gonzalez-Calbet, J. M. ; Bernhard, Christian ; Varela, M.

In: Physical Review B, 2015, vol. 91, no. 20, p. 205132

In this paper we present an atomic-resolution electron microscopy study of superlattices (SLs) where the colossal magnetoresistant manganite La0.67Ca0.33MnO3 (LCMO) and the high critical temperature superconducting cuprate La1.85Sr0.15CuO4 (LSCO) are combined. Although good quality epitaxial growth can be achieved, both the choice of substrate and the relatively large lattice mismatch between...

Université de Fribourg

Backfolded acoustic phonons as ultrasonic probes in metal-oxide superlattices

Lyzwa, Fryderyk ; 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...

Université de Fribourg

Charge dynamics of doped holes in high Tc cuprate superconductors: A clue from optical conductivity

Mishchenko, A. S. ; Nagaosa, N. ; Shen, Z.-X. ; Filippis, G. De ; Cataudella, V. ; Devereaux, T. P. ; Bernhard, Christian ; Kim, Kyung Wan ; Zaanen, J.

In: Physical Review Letters, 2008, vol. 100, no. 16, p. 166401

The charge dynamics in weakly hole doped high temperature superconductors is studied in terms of the accurate numerical solution to a model of a single hole interacting with a quantum lattice in an antiferromagnetic background, and accurate far-infrared ellipsometry measurements. The experimentally observed two electronic bands in the infrared spectrum can be identified in terms of the interplay...

Université de Fribourg

Clocking the onset of bilayer coherence in a high-${T}_{c}$ cuprate

Baldini, Edoardo ; Mann, Andreas ; Mallett, Benjamin P. P. ; Arrell, Christopher ; Mourik, Frank van ; Wolf, Thomas ; Mihailovic, Dragan ; Tallon, Jeffrey L. ; Bernhard, Christian ; Lorenzana, José ; Carbone, Fabrizio

In: Physical Review B, 2017, vol. 95, no. 2, p. 024501

In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature TC. Here we show via a combination of far-infrared ellipsometry and ultrafast broadband optical spectroscopy that signatures of such a state can be obtained via three independent observables in an underdoped sample of NdBa2Cu3O6+δ. The pseudogap correlations were disentangled from the...

Université de Fribourg

Coexistence and Competition of Magnetism and Superconductivity on the Nanometer Scale in Underdoped BaFe1.89Co0.11As₂

Marsik, Premysl ; Kim, Kyung Wan ; Dubroka, Adam ; Rössle, Matthias ; Malik, Vivek Kumar ; Schulz, Leander ; Wang, Chen Nan ; Niedermayer, Ch. ; Drew, Alan J. ; Willis, M. ; Wolf, T. ; Bernhard, Christian

In: Physical Review Letters, 2010, vol. 105, no. 5, p. 057001

We report muon spin rotation (μSR) and infrared spectroscopy experiments on underdoped BaFe1.89Co0.11As₂ which show that bulk magnetism and superconductivity (SC) coexist and compete on the nanometer length scale. Our combined data reveal a bulk magnetic order, likely due to an incommensurate spin density wave (SDW), which develops below Tmag≈32 K and...

Université de Fribourg

Coexistence of magnetic fluctuations and superconductivity in the pnictide high temperature superconductor SmFeAsO1-xFx measured by muon spin rotation

Drew, Alan J. ; Pratt, F. L. ; Lancaster, T. ; Blundell, S. J. ; Baker, P. J. ; Liu, R. H. ; Wu, G. ; Chen, X. H. ; Watanabe, I. ; Malik, Vivek Kumar ; Dubroka, Adam ; Kim, Kyung Wan ; Rössle, Matthias ; Bernhard, Christian

In: Physical Review Letters, 2008, vol. 101, no. 9, p. 097010

Muon spin rotation experiments were performed on the pnictide high temperature superconductor SmFeAsO1-xFx with x=0.18 and 0.3. We observed an unusual enhancement of slow spin fluctuations in the vicinity of the superconducting transition which suggests that the spin fluctuations contribute to the formation of an unconventional superconducting state. An...