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

Future directions of μSR—laser excitation

Yokoyama, K. ; Murahari, P. ; Heathcote, P. ; Nuccio, Laura ; Lord, J. S. ; Morley, N. A. ; Drew, Alan J.

In: Physica Scripta, 2014, vol. 88, no. 6, p. 068511

We discuss the general principles of laser-excited muon pump–probe spin spectroscopy (photo-μSR), including the historical origins of the technique, and discuss the overall experimental method. We review examples of past work using this technique, then discuss the future upgrade of the HiFi spectrometer with a high-power laser system. In particular, we note that performing photo-μSR...

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

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

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...