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Stuttgart Mühlhausen, Germany

Liu Y.,Max Planck Institute For Festkoperforschung | Lin C.T.,Max Planck Institute For Festkoperforschung
Journal of Superconductivity and Novel Magnetism

Single crystals of Fe 1+δTe 1-xSe x (0 ≤ x ≤ 0.5) were grown via both Bridgman and self-flux techniques. Large crystals of size ∅10 × 50 mm could be obtained with the Bridgman method. The excess of iron, δ ≥ 0.07, at interstitial sites was observed to deteriorate the superconductivity of the samples. Study of semiconducting and Curie-Weiss-like behavior indicates that an appearance of a hump for Fe 1+δTe 0.60Se 0.40 (δ ≤ 0.04) is more pronounced for the self-flux growth than for the Bridgman method. This was observed via measurement of the normal state of resistivity and magnetic susceptibility, which decrease with lower temperature. Furthermore, our results give evidence that the phase with x ∼ 0.40 is readily formed in the self-flux method despite the use of various ratios of initial mixtures. © Springer Science+Business Media, LLC 2010. Source

Peng J.B.,Max Planck Institute For Festkoperforschung | Lin C.T.,Max Planck Institute For Festkoperforschung
Journal of Superconductivity and Novel Magnetism

High-quality and various doped Bi 2Sr 2-xLa xCuO 6+δ (x = 0-0.90) single crystals were obtained by floating-zone method. Analysis of the thermal behavior indicated an incongruent melt for all the doped compounds. The segregation coefficient of La related to Sr was estimated to be ∼1.02. Chemical compositions including the La doping in the crystals were accurately determined to study the effect of doping on the structural, chemical and superconducting property of the compounds. Raman spectra were performed to show the high-frequency modes 627 cm -1 softened with increasing the doping level of La. Implications of the doping effect on crystals for understanding the superconductivity are discussed. © Springer Science+Business Media, LLC 2010. Source

Stavrou E.,National Technical University of Athens | Stavrou E.,Max Planck Institute For Festkoperforschung | Raptis C.,National Technical University of Athens | Syassen K.,Max Planck Institute For Festkoperforschung
Physical Review B - Condensed Matter and Materials Physics

The Raman spectra of three (TeO2)1-x(ZnO)x (x=0.1, 0.2, and 0.4) glasses have been measured under pressure up to 13 GPa. We report an unusual pressure dependence of the Boson peak frequency which is quite different from that observed in relevant experiments for other network glasses or predicted by theory. The unexpected observed effect indicates that tellurite glasses respond like elastic, rather than plastic, media to both compression and decompression treatments. We suggest that, with respect to plastic versus elastic deformation mode, the behavior of glasses under pressure is not universal. Further, we conclude that a medium range order elastic glass-to-glass transition from a rigid to a more flexible network is induced by pressure for two of the glasses (x=0.2 0.4). This transition is reversible upon decompression, merely exhibiting a small hysteresis. © 2010 The American Physical Society. Source

Kim Y.,Pohang University of Science and Technology | Kim Y.,Max Planck Institute For Festkoperforschung | Lee D.S.,Korea Institute of Science and Technology | Jung S.,Korea Research Institute of Standards and Science | And 6 more authors.
Nano Letters

We have investigated fractional quantum Hall (QH) states in Bernal-stacked bilayer graphene using transconductance fluctuation measurements. A variety of odd-denominator fractional QH states with νQH → νQH + 2 symmetry, as previously reported, are observed. However, surprising is that also particle-hole symmetric states are clearly resolved in the same measurement set. We attribute their emergence to the reversal of orbital states in the octet level scheme induced by a strong local charge imbalance, which can be captured by the transconductance fluctuations. Also the even-denominator fractional QH state at filling -1/2 is observed. However, contrary to a previous study on a suspended graphene layer [ Ki et al. Nano Lett. 2014, 14, 2135 ], the particle-hole symmetric state at filling 1/2 is detected as well. These observations suggest that the stability of both odd and even denominator fractional QH states is very sensitive to local transverse electric fields in bilayer graphene. © 2015 American Chemical Society. Source

Kim J.-H.,Max Planck Institute For Festkoperforschung | Vrejoiu I.,Max Planck Institute of Microstructure Physics | Khaydukov Y.,Max Planck Institute For Festkoperforschung | Keller T.,Max Planck Institute For Festkoperforschung | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics

We have investigated the magnetization profiles in superlattices composed of the two ferromagnets La 0.7Sr 0.3MnO 3 and SrRuO 3 using spin-polarized neutron reflectometry. In combination with magnetometry, the neutron data indicate a noncollinear spin configuration where orientation of the Ru moments changes from in plane at the interface to out of plane deep inside the SrRuO 3 layers. The spin structure originates in a competition between antiferromagnetic exchange interactions of Mn and Ru moments across the interface, and the magnetocrystalline anisotropy of the Ru moments, and it is closely related to the "exchange spring" structures previously observed in multilayers composed of ferromagnetic elements and alloys. © 2012 American Physical Society. Source

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