Université de Fribourg

Low-energy interband transitions in the infrared response of Ba(Fe1-xCox)2As2

Maršík, Premysl ; Wang, Chen Nan ; Rössle, Matthias ; Yazdi-Rizi, M. ; Schuster, Roman ; Kim, Kyung Wan ; Dubroka, Adam ; Munzar, Dominik ; Wolf, T. ; Chen, X. H. ; Bernhard, Christian

In: Physical Review B, 2014, vol. 88, no. 18, p. 180508

We studied the doping and temperature (T) dependence of the infrared (IR) response of Ba(Fe1−xCox)2As2 single crystals. We show that a weak band around 1000 cm−1, that was previously interpreted in terms of interaction of the charge carriers with magnetic excitations or of a pseudogap, is rather related to low-energy interband transitions. Specifically, we show that this band exhibits a...

Université de Fribourg

Evidence of a Precursor Superconducting Phase at Temperatures as High as 180 K in RBa₂Cu₃O7-δ (R=Y,Gd,Eu) Superconducting Crystals from Infrared Spectroscopy

Dubroka, Adam ; Rössle, Matthias ; Kim, Kyung Wan ; Malik, Vivek Kumar ; Munzar, Dominik ; Basov, D. N. ; Schafgans, A. A. ; Moon, S. J. ; Lin, C. T. ; Haug, D. ; Hinkov, V. ; Keimer, B. ; Wolf, Th. ; Storey, J. G. ; Tallon, Jeffery L. ; Bernhard, Christian

In: Physical Review Letters, 2011, vol. 106, no. 4, p. 047006

We show that a multilayer analysis of the infrared c-axis response of RBa₂Cu₃O7-δ (R=Y,Gd,Eu) provides important new information about the anomalous normal-state properties of underdoped cuprate high temperature superconductors. In addition to competing correlations which give rise to a pseudogap that depletes the low-energy electronic states below...

Université de Fribourg

Evidence for multiple superconducting gaps in optimally doped BaFe1.87Co0.13As₂ from infrared spectroscopy

Kim, Kyung Wan ; Rössle, Matthias ; Dubroka, Adam ; Malik, Vivek Kumar ; Wolf, Th. ; Bernhard, Christian

In: Physical Review B, 2010, vol. 81, p. 214508

We performed combined infrared reflection and ellipsometry measurements of the in-plane optical response of single crystals of the pnictide high-temperature superconductor BaFe1.87Co0.13As₂ with Tc=24.5 K. Our experimental data provide evidence for multiple superconducting energy gaps and can be well described in terms of three isotropic gaps with...

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

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

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...

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

Intrinsic Mobility Limit for Anisotropic Electron Transport in Alq₃

Drew, Alan J. ; Pratt, F. L. ; Hoppler, Justin ; Schulz, Leander ; Malik, Vivek Kumar ; Morley, N. A. ; Desai, P. ; Shakya, P. ; Kreouzis, T. ; Gillin, W. P. ; Kim, Kyung Wan ; Dubroka, Adam ; Scheuermann, R.

In: Physical Review Letters, 2008, vol. 100, p. 116601

Muon spin relaxation has been used to probe the charge carrier motion in the molecular conductor Alq₃ (tris[8-hydroxy-quinoline] aluminum). At 290 K, the magnetic field dependence of the muon spin relaxation corresponds to that expected for highly anisotropic intermolecular electron hopping. Intermolecular mobility in the fast hopping direction has been found to be 0.23±0.03 cm² V⁻¹ s⁻¹...