Université de Fribourg

Temporal mapping of photochemical reactions and molecular excited states with carbon specificity

Wang, K. ; Murahari, P. ; Yokoyama, K. ; Lord, J. S. ; Pratt, F. L. ; He, J. ; Schulz, Leander ; Willis, M. ; Anthony, J. E. ; Morley, N. A. ; Nuccio, Laura ; Misquitta, A. ; Dunstan, D. J. ; Shimomura, K. ; Watanabe, I. ; Zhang, S. ; Heathcote, P. ; Drew, Alan J.

In: Nature Materials, 2017, vol. 16, no. 4, p. 467–473

Photochemical reactions are essential to a large number of important industrial and biological processes. A method for monitoring photochemical reaction kinetics and the dynamics of molecular excitations with spatial resolution within the active molecule would allow a rigorous exploration of the pathway and mechanism of photophysical and photochemical processes. Here we demonstrate that...

Université de Fribourg

Muonium avoided level crossing measurement of electron spin relaxation rate in a series of substituted anthradithiophene based molecules

Han, S. ; Wang, K. ; Willis, M. ; Nuccio, Laura ; Pratt, F.L. ; Lord, J.S. ; Thorley, K.J. ; Anthony, J. ; Drew, A.J. ; Zhang, S. ; Schulz, Leander

In: Synthetic Metals, 2015, vol. 208, p. 39–42

Muon spin spectroscopy and in particular the avoided level crossing technique is introduced, with the aim of showing it as a very sensitive local probe for electron spin relaxation in organic semiconductors. Avoided level crossing data on tert-butyl-ethynyl anthradithiophene, tri-methyl-silyl-ethynyl anthradithiophene and tri-ethygermyl-ethynyl anthradithiophene at different temperatures are...

Université de Fribourg

Importance of spin-orbit interaction for the electron spin relaxation in organic semiconductors

Nuccio, L. ; Willis, M. ; Schulz, Leander ; Fratini, S. ; Messina, F. ; D’Amico, M. ; Pratt, F. L. ; Lord, J. S. ; McKenzie, I. ; Loth, M. ; Purushothaman, B. ; Anthony, J. ; Heeney, M. ; Wilson, R. M. ; Hernández, I. ; Cannas, M. ; Sedlak, K. ; Kreouzis, T. ; Gillin, W. P. ; Bernhard, Christian ; Drew, Alan J.

In: Physical Review Letters, 2013, vol. 110, no. 21, p. 216602

Despite the great interest organic spintronics has recently attracted, there is only a partial understanding of the fundamental physics behind electron spin relaxation in organic semiconductors. Mechanisms based on hyperfine interaction have been demonstrated, but the role of the spin-orbit interaction remains elusive. Here, we report muon spin spectroscopy and time-resolved photoluminescence...

Université de Fribourg

Muon spin rotation study of magnetism and superconductivity in Ba(Fe1−xCox)₂As₂ single crystals

Bernhard, Christian ; Wang, Chen Nan ; Nuccio, Laura ; Schulz, Leander ; Zaharko, O. ; Larsen, J. ; Aristizabal, C. ; Willis, M. ; Drew, Alan J. ; Varma, G. D. ; Wolf, T. ; Niedermayer, Ch.

In: Physical Review B - Condensed Matter and Materials Physics, 2012, vol. 86, no. 14, p. 144112

Using muon spin rotation (μSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1−xCox)₂As₂ single crystals with 0≤x≤0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity. In the nonsuperconducting samples at 0

Université de Fribourg

Importance of intramolecular electron spin relaxation in small molecule semiconductors

Schulz, Leander ; Willis, M. ; Nuccio, L. ; Shusharov, P. ; Fratini, S. ; Pratt, F. L. ; Gillin, W. P. ; Kreouzis, T. ; Heeney, M. ; Stingelin, N. ; Stafford, C. A. ; Beesley, D. J. ; Bernhard, Christian ; Anthony, J. E. ; McKenzie, I. ; Lord, J. S. ; Drew, Alan J.

In: Physical Review B: Condensed Matter and Materials Physics, 2011, vol. 84, no. 8, p. 085209

Electron spin relaxation rate (eSR) is investigated on several organic semiconductors of different morphologies and molecular structures, using avoided level crossing muon spectroscopy as a local spin probe. We find that two functionalized acenes (polycrystalline tri(isopropyl)silyl-pentacene and amorphous 5,6,11,12- tetraphenyltetracene) exhibit eSRs with an Arrhenius-like temperature...

Université de Fribourg

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer

Schulz, Leander ; Nuccio, L. ; Willis, M. ; Desai, P. ; Shakya, P. ; Kreouzis, T. ; Malik, Vivek Kumar ; Bernhard, Christian ; Pratt, F. L. ; Morley, N. A. ; Suter, A. ; Nieuwenhuys, G. J. ; Prokscha, T. ; Morenzoni, E. ; Gillin, W. P. ; Drew, Alan J.

In: Nature Materials, 2011, vol. 10, p. 39–44

Spintronics has shown a remarkable and rapid development, for example from the initial discovery of giant magnetoresistance in spin valves (Baibich, M. N. et al. Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices. Phys. Rev. Lett. 61, 2472–2475, 1988) to their ubiquity in hard-disk read heads in a relatively short time. However, the ability to fully harness electron spin as...

Université de Fribourg

Elastic torsion effects in magnetic nanoparticle diblock-copolymer structures

Schulz, Leander ; Schirmacher, W. ; Omran, A. ; Shah, V. R. ; Böni, P. ; Petry, W. ; Müller-Buschbaum, P.

In: Journal of Physics: Condensed Matter, 2010, vol. 22, no. 34, p. 346008

Magnetic properties of thin composite films, consisting of non-interacting polystyrene-coated γ-Fe₂O₃ (maghemite) nanoparticles embedded into polystyrene-block-polyisoprene P(S-b-I) diblock-copolymer films are investigated. Different particle concentrations, ranging from 0.7 to 43 wt%, have been used. The magnetization measured as a function of external field and temperature...

Université de Fribourg

Incommensurate magnetic order and dynamics induced by spinless impurities in YBa₂Cu₃O6.6

Suchaneck, A. ; Hinkov, V. ; Haug, D. ; Schulz, Leander ; Bernhard, Christian ; Ivanov, A. ; Hradil, K. ; Lin, C. T. ; Bourges, P. ; Keimer, B. ; Sidis, Y.

In: Physical Review Letters, 2010, vol. 105, p. 037207

We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa₂Cu₃O6.6, an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale...

Université de Fribourg

Dynamical response and confinement of the electrons at the LaAlO₃/SrTiO₃ interface

Dubroka, Adam ; Rössle, Matthias ; Kim, Kyung Wan ; Malik, Vivek Kumar ; Schulz, Leander ; Thiel, S. ; Schneider, C. W. ; Mannhart, J. ; Herranz, G. ; Copie, O. ; Bibes, M. ; Barthélémy, A. ; Bernhard, Christian

In: Physical Review Letters, 2010, vol. 104, p. 156807

With infrared ellipsometry and transport measurements we investigated the electrons at the interface between LaAlO₃ and SrTiO₃. We obtained a sheet carrier concentration of Ns≈5–9×10¹³ cm⁻², an effective mass of m*=3.2±0.4me, and a strongly frequency dependent mobility. The latter are similar as in bulk SrTi1-xNbxO₃ and...

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...