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Université de Fribourg

Muon spin rotation study of magnetism and superconductivity in BaFe2−xCoxAs₂ and Pr1−xSrxFeAsO

Bernhard, Christian ; Drew, Alan J. ; Schulz, Leander ; Malik, Vivek Kumar ; Rössle, Matthias ; Niedermayer, Ch. ; Wolf, Th. ; Varma, G. D. ; Mu, G. ; Wen, H.-H. ; Liu, H. ; Wu, G. ; Chen, X. H.

In: New Journal of Physics, 2009, vol. 11, p. 055050

We present a muon spin rotation (μSR) study of the magnetic and superconducting properties of single crystals of electron-doped BaFe2−xCoxAs₂ with x = 0.08, 0.20 and 0.25 (Tc = 9, 25 and 20 K) and of polycrystalline hole-doped Pr1−xSrxFeAsO with x = 0 and 0.2 (Tc = 15...

Université de Fribourg

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation

Drew, Alan J. ; Hoppler, Julian ; Schulz, Leander ; Pratt, F. L. ; Desai, P. ; Shakya, P. ; Kreouzis, T. ; Gillin, W. P. ; Suter, A. ; Morley, N. A. ; Malik, Vivek Kumar ; Dubroka, Adam ; Kim, Kyung Wan ; Bouyanfif, Houssny ; Bourqui, Francis ; Bernhard, Christian ; Scheuermann, R. ; Nieuwenhuys, G. J. ; Prokscha, T. ; Morenzoni, E.

In: Nature Materials, 2009, vol. 8, p. 109 - 114

Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the...

Université de Fribourg

X-ray study of structural domains in the near-surface region of SrTiO₃ substrates with Y0.6Pr0.4Ba₂Cu₃O₇/La2/3Ca1/3MnO₃ superlattices grown on top

Hoppler, Justin ; Stahn, J. ; Bouyanfif, Houssny ; Malik, Vivek Kumar ; Patterson, B. D. ; Willmott, P. R. ; Cristiani, G. ; Habermeier, H.-U. ; Bernhard, Christian

In: Physical Review B, 2008, vol. 78, no. 13, p. 134111

We investigated with synchrotron x-ray diffraction and reflectometry the formation of structural domains in the near-surface region of single crystalline SrTiO₃ (001) substrates with Y0.6Pr0.4Ba₂Cu₃O₇/La2/3Ca1/3MnO₃ superlattices grown on top. We find that the antiferrodistortive cubic to tetragonal transition, which occurs at...

Université de Fribourg

Superconducting energy gap and c-axis plasma frequency of (Nd,Sm)FeAsO0.82F0.18 superconductors from infrared ellipsometry

Dubroka, Adam ; Kim, Kyung Wan ; Rössle, Matthias ; Malik, Vivek Kumar ; Drew, Alan J. ; Liu, R. H. ; Wu, G. ; Chen, X. H. ; Bernhard, Christian

In: Physical Review Letters, 2008, vol. 101, no. 9, p. 097011

We present far-infrared ellipsometric measurements of polycrystalline samples of the pnictide superconductor RFeAsO0.82F0.18 (R=Nd and Sm). We find evidence that the electronic properties are strongly anisotropic such that the optical spectra are dominated by the weakly conducting c-axis response similar to the cuprate high-temperature superconductors....

Université de Fribourg

Optical study of the free-carrier response of LaTiO₃/SrTiO₃ superlattices

Seo, S. S. A. ; Choi, W. S. ; Lee, H. N. ; Yu, Li ; Kim, Kyung Wan ; Bernhard, Christian ; Noh, T. W.

We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO₃/SrTiO₃ superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface ≈3×10¹⁴ cm⁻². This is probably due to the leakage of d electrons at...

Université de Fribourg

Electronic Liquid Crystal State in the High-Temperature Superconductor YBa₂Cu₃O6.45

Hinkov, V. ; Haug, D. ; Fauqué, B. ; Bourges, P. ; Sidis, Y. ; Ivanov, A. ; Bernhard, Christian ; Lin, C. T. ; Keimer, B.

In: Science, 2008, vol. 319, p. 597-600

Electronic phases with symmetry properties matching those of conventional liquid crystals have recently been discovered in transport experiments on semiconductor heterostructures and metal oxides at millikelvin temperatures. We report the spontaneous onset of a one-dimensional, incommensurate modulation of the spin system in the high-transition-temperature superconductor...

Université de Fribourg

Optical response of ferromagnetic YTiO₃ studied by spectral ellipsometry

Kovaleva, N. N. ; Boris, A. V. ; Yordanov, P. ; Maljuk, A. ; Brücher, E. ; Strempfer, J. ; Konuma, M. ; Zegkinoglou, I. ; Bernhard, Christian ; Stoneham, A. M. ; Keimer, B.

In: Physical Review B: Condensend Matter and Materials Physics, 2007, vol. 76, no. 15, p. 155125

We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO₃ single crystal with ferromagnetic Curie temperature TC=30 K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7 eV....

Université de Fribourg

Isotope effect on the optical phonons of YBa₂Cu₄O₈ studied by far-infrared ellipsometry and Raman scattering

Trajnerowicz, A. ; Golnik, A. ; Bernhard, Christian ; Machtoub, L. ; Ulrich, C. ; Tallon, J. L. ; Cardona, M.

In: Physical Review B, 2006, vol. 74, p. 104513

The phonon spectra of YBa₂Cu₄O₈ polycrystalline samples with different isotope substitution for Ba, Cu, and O have been studied using far-infrared ellipsometry and Raman scattering. The observed isotope shifts of Raman- and infrared-active phonons provide insight into their relative Ba, Cu, and O normal mode content. This allows us to examine mode eigenvectors obtained from lattice...