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[en] To clarify the order parameter symmetry of cuprates, the magnetic penetration depth was measured along the crystallographic directions a,b, and c in single crystals of YBa2Cu4O8 via muon spin rotation. This method is direct, bulk sensitive, and unambiguous. The temperature dependences of the penetration depth along the crystallographic a- and b-directions were found to exhibit an inflection point at low temperatures as is typical and provides evidence for two-gap superconductivity (TGS) with s+d wave character in the planes. In contrast, the penetration depth along the c-axis shows almost pure s wave character which never met the awareness of the community thereby highlighting the important role of c-axis effects. We conclude that TGS is a generic and universal feature in the bulk of cuprates
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; 
; CODEN VDPEAZ; v. 43(1); [1 p.]
; CODEN VDPEAZ; v. 43(1); [1 p.]
[en] LuFe4Ge2 is a geometrically frustrated magnetic system with antiferromagnetic (AFM) ordering at TN = 36 K. In this work, we used μSR spectroscopy to study the pressure evolution of magnetic phase diagram of LuFe4Ge2. Previous electrical transport investigations showed a continuous suppression of TN to zero temperature at 1.7 GPa and suggested the existence of a second pressure-induced magnetic phase. Our transverse field - μSR experiments find a 100% magnetic volume below TN in the low pressure AFM phase. Further, they prove the presence of a second long-range antiferromagnetically ordered phase at higher pressures and also indicate that the complete sample volume is magnetically ordered in this phase. The obtained ordering temperatures are in good agreement with the electrical resistivity data. The low temperature muon precision frequency does not change between zero and 2.25 GPa, which is consistent with a similar size of the ordered moment in the two different magnetic phases.
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; (Dresden 2017 issue); [1 p.]
; CODEN VDPEAZ; (Dresden 2017 issue); [1 p.]
[en] The discovery of a new class of superconducting materials, ReFeAsO1-xFx, stirred up the scientific community. Here we report the Gd3+ high field ESR study of differently doped (La,Gd)FeAsO1-xFx compounds. In lightly Gd-doped LaFeAsO samples the SDW transition yields line-broadening at the transition temperature, the SDW transition is then suppressed upon F-doping. In the dense compound, GdFeAsO, with SDW transition around 140 K, the Gd-ESR was also studied. With 15% F-doping superconductivity appears at ∝ 21 K. The SDW and SC transitions are clearly seen in ESR and in μ SR as well. Surprisingly the reminiscence of the SDW transition of the undoped material (GdFeAsO) was identified in the doped (15% F) compound at lower temperature (∝ 80 K). This indicates the importance of the the interplay between superconductivity and magnetism in oxypnictides.
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; (Dresden 2009 issue); [1 p.]
; CODEN VDPEAZ; (Dresden 2009 issue); [1 p.]
No abstract available
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; v. 41(1); [1 p.]
; CODEN VDPEAZ; v. 41(1); [1 p.]
[en] Among intermetallics, gallium cluster phases - the compounds, which crystal structures are built by gallium-based polyhedra with high coordination numbers - are promising candidates for unconventional superconductivity. In this class of compounds, ReGa, MoGa, MoGa, RhGa and IrGa are known to superconduct at low temperatures. Among the series, MoGa exhibits the largest superconducting transition temperature of T = 9.7 K in zero magnetic field. In our study, we focused on MoGa, aiming at the investigation of its macro- and microscopic properties. For this purpose, thermodynamic measurements as well as muon spin spectroscopy technique were employed. According to the specific heat measurements and transverse-field muon spin rotation/relaxation experiments, we classify MoGa as a strong-coupled superconductor with two s-wave superconducting gaps.
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; (Berlin 2018 issue); [1 p.]
; CODEN VDPEAZ; (Berlin 2018 issue); [1 p.]
[en] Here, the temperature dependence of the in-plane magnetic penetration depth (λab) in an extensively characterized sample of superconducting CaKFe4As4(Tc≃35K) was investigated using muon-spin rotation (μSR). A comparison of λ–2ab(T) measured by μSR with the one inferred from angle-resolved photoemission spectroscopy (ARPES) data confirms the presence of multiple gaps at the Fermi level. An agreement between μSR and ARPES requires the presence of additional bands, which are not resolved by ARPES experiments. These bands are characterized by small superconducting gaps with an average zero-temperature value of Δ0=2.4(2)meV. Our data suggest that in CaKFe4As4 the s± order parameter symmetry acquires a more sophisticated form by allowing a sign change not only between electron and hole pockets, but also within pockets of similar type.
Journal
Physical Review B; ISSN 2469-9950; ; v. 97(14); vp
; v. 97(14); vp
[en] The electronic structure of the iron chalcogenide superconductors FeSe_1_-_x and Rb_0_._7_7Fe_1_._6_1Se_2 was investigated by high-resolution angle-resolved photoemission spectroscopy (ARPES). The results were compared to DFT calculations and μSR measurements. Both compounds share ''cigar-shaped'' Fermi surface sheets in their electronic structure, that can be found in almost all iron-pnictide superconductors. These features originate from a strong interplay of two hole- and electron-like bands in the Brillouin zone center, leading to a pronounced singularity in the density of states just below the Fermi level. This facilitates the coupling to a bosonic mode responsible for superconductivity.
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; (Dresden 2014 issue); [1 p.]
; CODEN VDPEAZ; (Dresden 2014 issue); [1 p.]
[en] We report on the local magnetic properties of the series of ferromagnetic (FM) materials RCoLnO (R = La, Pr, Nd, Sm; Ln = As, P) as investigated by means of muon spin spectroscopy under pressure P and electron spin resonance (ESR). The effect of P is shown to be quantitatively equivalent to the chemical lattice shrinkage triggered by the different ionic radii of R ions. This is verified for both experimental-dependent quantities (i.e., magnetic field at the muon site) and for intrinsically material-dependent properties (i.e., FM critical temperature T_C). Results of ESR in a wide range of temperature and magnetic field clearly display that magnetism is of localized nature, despite the overall metallic behaviour of these materials.
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; (Berlin 2015 issue); [1 p.]
; CODEN VDPEAZ; (Berlin 2015 issue); [1 p.]
[en] We report on the effect of nearly-hydrostatic pressure P ≤ 23 kbar in an optimally-doped LaFeAsO_1_-_xF_x sample. Our results of muon spin rotation show no dependence of T_c on P and, at the same time, a remarkable enhancement of the superfluid density (n_s). This is a dramatic effect, the saturation value of n_s being increased by ∝ 30 % at the maximum P value. We provide evidence from density-functional theory (DFT) calculations that this increase should not be associated to an induced change in the fermiology of LaFeAsO_1_-_xF_x. Accordingly, we suggest that the experimental data can be explained by assuming a modification of the ratio between intra- and inter-band impurity scattering, only possible in multi-band SC.
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; (Berlin 2015 issue); [1 p.]
; CODEN VDPEAZ; (Berlin 2015 issue); [1 p.]
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