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Université de Fribourg

Infrared study of the spin reorientation transition and its reversal in the superconducting state in underdoped ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$

Mallett, B. P. P. ; Maršík, Premysl ; Yazdi-Rizi, M. ; Wolf, Th. ; Böhmer, A. E. ; Hardy, F. ; Meingast, C. ; Munzar, Dominik ; Bernhard, Christian

In: Physical Review Letters, 2015, vol. 115, no. 2, p. 027003

With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba1−xKxFe2As2. In agreement with the predicted transition from a single-Q to a double-Q AF structure, we found that a distinct spin density wave develops in the...

Université de Fribourg

Evidence for precursor superconducting pairing above T c in underdoped cuprates from an analysis of the in-plane infrared response

Šopík, B. ; Chaloupka, Jiří ; Dubroka, Adam ; Bernhard, Christian ; Munzar, Dominik

In: New Journal of Physics, 2015, vol. 17, no. 5, p. 053022

We performed calculations of the in-plane infrared response of underdoped cuprate superconductors to clarify the origin of a characteristic dip feature which occurs in the published experimental spectra of the real part of the in-plane conductivity below an onset temperature ${{T}^{{\rm ons}}}$ considerably higher than ${{T}_{{\rm c}}}$. We provide several arguments, based on a detailed...

Université de Fribourg

Atomic-resolution studies of epitaxial strain release mechanisms in $\mathrm{L}{\mathrm{a}}_{1.85}\mathrm{S}{\mathrm{r}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4}/\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{C}{\mathrm{a}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ superlattices

Biškup, N. ; Das, Saikat ; Gonzalez-Calbet, J. M. ; Bernhard, Christian ; Varela, M.

In: Physical Review B, 2015, vol. 91, no. 20, p. 205132

In this paper we present an atomic-resolution electron microscopy study of superlattices (SLs) where the colossal magnetoresistant manganite La0.67Ca0.33MnO3 (LCMO) and the high critical temperature superconducting cuprate La1.85Sr0.15CuO4 (LSCO) are combined. Although good quality epitaxial growth can be achieved, both the choice of substrate and the relatively large lattice mismatch between...

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

Effect of combined addition of graphene oxide and citric acid on superconducting properties of MgB₂Effect of combined addition of graphene oxide and citric acid on superconducting properties of MgB₂

Sudesh ; Das, Saikat ; Bernhard, Christian ; Varma, G. D.

In: Physica C: Superconductivity and its Applications, 2015, vol. 509, p. 49–55

In the present work, polycrystalline samples with compositions MgB₂ + 3wt% GO + x wt% C₆H₈O₇ (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C₆H₈O₇) on superconducting properties of MgB₂. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB₂ with space...

Université de Fribourg

X-ray absorption spectroscopy study of the electronic and magnetic proximity effects in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ and ${\mathrm{La}}_{2$-${}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ multilayers

Uribe-Laverde, Miguel Angel ; Das, Saikat ; Sen, Kaushik ; Marozau, Ivan ; Perret, E. ; Alberca, A. ; Heidler, J. ; Piamonteze, C. ; Merz, M. ; Nagel, P. ; Schuppler, S. ; Munzar, Dominik ; Bernhard, Christian

In: Physical Review B, 2014, vol. 90, no. 20, p. 205135

With x-ray absorption spectroscopy we investigated the orbital reconstruction and the induced ferromagnetic moment of the interfacial Cu atoms in YBa2Cu3O7/La2/3Ca1/3MnO3 (YBCO/LCMO) and La2−xSrxCuO4/La2/3Ca1/3MnO3 (LSCO/LCMO) multilayers. We demonstrate that these electronic and magnetic proximity effects are coupled and are common to these cuprate/manganite multilayers. Moreover, we show that...

Université de Fribourg

Enhanced superconducting properties of rare-earth oxides and graphene oxide added MgB₂

Sudesh ; Das, S. ; Bernhard, Christian ; Varma, G.D.

In: Physica C: Superconductivity, 2014, vol. 505, p. 32–38

In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare-earth (RE, RE = La, Sm, Eu, Gd, Tb and Ho) oxides (REO) and (iii) a mixture of GO and rare-earth oxides (GO + REO) on the superconducting properties of MgB₂, have been studied with the help of electrical transport and magnetic measurements. All the samples have been prepared following the standard...

Université de Fribourg

Controlling the near-surface superfluid density in underdoped YBa₂Cu₃O6+x by photo-illumination

Stilp, E. ; Suter, A. ; Prokscha, T. ; Salman, Z. ; Morenzoni, E. ; Keller, H. ; Pahlke, P. ; Hühne, R. ; Bernhard, Christian ; Liang, Ruixing ; Hardy, W. N. ; Bonn, D. A. ; Baglo, J. C. ; Kiefl, R. F.

In: Scientific Reports, 2014, vol. 4, p. -

The interaction with light weakens the superconducting ground state in classical superconductors. The situation in cuprate superconductors is more complicated: illumination increases the charge carrier density, a photo-induced effect that persists below room temperature. Furthermore, systematic investigations in underdoped YBa₂Cu₃O6+x (YBCO) have shown an enhanced critical...

Université de Fribourg

Influence of La and Mn vacancies on the electronic and magnetic properties of LaMnO₃ thin films grown by pulsed laser deposition

Marozau, Ivan ; Das, Proloy T. ; Döbeli, Max ; Storey, James G. ; Uribe-Laverde, Miguel A. ; Das, Saikat ; Wang, Chennan ; Rössle, Matthias ; Bernhard, Christian

In: Physical Review B, 2014, vol. 89, no. 17, p. 174422

With pulsed laser deposition, we have grown c axis oriented thin films of the nominal composition LaMnO3 (LMO) on LSAT(001) substrates. We find that, depending on the oxygen background pressure during growth, the LMO films contain sizeable amounts of La and/or Mn vacancies that strongly influence their electronic and magnetic properties. Specifically, we show that the Mn/La ratio can be...