Université de Fribourg

Competing superconducting and magnetic order parameters and field-induced magnetism in electron-doped $\mathrm{Ba}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x})}_{2}{\mathrm{As}}_{2}$

Larsen, J. ; Mencia Uranga, B. ; Stieper, G. ; Holm, S. L. ; Bernhard, Christian ; Wolf, T. ; Lefmann, K. ; Andersen, B. M. ; Niedermayer, Christof

In: Physical Review B, 2015, vol. 91, no. 2, p. 024504

We have studied the magnetic and superconducting properties of Ba(Fe0.95Co0.05)2As2 as a function of temperature and external magnetic field using neutron scattering and muon spin rotation. Below the superconducting transition temperature the magnetic and superconducting order parameters coexist and compete. A magnetic field can significantly enhance the magnetic scattering in the superconducting...

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

Transient spin density wave order induced in the normal state of BaFe 2 As 2 by coherent lattice oscillations

Kim, Kyung Wan ; Pashkin, A. ; Schäfer, H. ; Beyer, M. ; Porer, M. ; Wolf, T. ; Bernhard, Christian ; Demsar, J. ; Huber, R. ; Leitenstorfer, A.

In: EPJ Web of Conferences, 2013, vol. 41, p. 03012

We trace the ultrafast dynamics of the spin density wave gap of the pnictide system BaFe2As2 probing resonantly with broadband multi-terahertz pulses. The photoexcitation in the low-temperature ground state leads to a fast suppression of the spin order followed by a slower recovery process. Surprisingly, in the normal state, we observe periodic oscillations of the spin density wave feature at a...

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

Macroscopic phase segregation in superconducting K0.73Fe1.67Se₂ as seen by muon spin rotation and infrared spectroscopy

Wang, Chen Nan ; Maršik, Premysl ; Schuster, Roman ; Dubroka, Adam ; Rössle, Matthias ; Niedermayer, Ch. ; Varma, G. D. ; Wang, A. F. ; Chen, X. H. ; Wolf, T. ; Bernhard, Christian

In: Physical Review B - Condensed matter and materials physics, 2012, vol. 85, no. 21, p. 214503

Using muon spin rotation and infrared spectroscopy, we investigated the recently discovered superconductor K0.73Fe1.67Se₂ with Tc≈32 K. We show that the combined data can be consistently described in terms of a macroscopically phase-segregated state with a matrix of ∼88% volume fraction that is insulating and strongly magnetic and inclusions with an ∼12%...

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...