Suppressed superconductivity in charge-doped Li(Fe1 − x x
Saicharan AswarthamG. BehrLuminita HarnageaDirk BomborA. R. BachmannИ. В. МорозовV. B. ZabolotnyyA. A. KordyukT. K. KimD. V. EvtushinskyС. В. БорисенкоA. U. B. WolterC. HeßS. WurmehlB. Büchner
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Single crystals of the new unconventional superconductor LiFe${}_{1\ensuremath{-}x}$Co${}_{x}$As with $x$$=$ 0, 0.025, 0.05 were grown by a new approach using the self-flux technique. The superconducting transition temperature was found to decrease upon Co doping at the Fe site. Apparently, in LiFeAs this doping scheme suppresses superconductivity, in contrast to the effects of Co doping in other Fe-As compounds, where it suppresses the spin-density wave and establishes superconductivity. Angle-resolved photoemission spectroscopy shows that the bottom of electron-like bands sinks by about 17 meV upon $5%$ Co doping, which indicates that the chemical substitution of Co for Fe in LiFeAs results in charge doping.We report on the first observation of a double suppression of superconductivity in a superconductor/ferromagnet layered system. The result was obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu41Ni59 with dNb ≊ 6.2 nm. As the thickness of the ferromagnetic alloy gradually increases, the superconducting transition temperature Tc drops sharply until a complete suppression of superconductivity is observed at dcuNi ≊ 2.5 nm. At further increase of the Cu41Ni59 layer thickness, superconductivity restores at dcuNi ≊ 24 nm. Then, with a subsequent increase of dcuNi, superconductivity vanishes again at dcuNi ≊ 38 nm. Our experiments give evidence for the realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic alloy layer.
Superconducting transition temperature
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Suppression of superconductivity due to the proximity effect between a superconductor and a ferromagnet can be partially alleviated when a Cooper pair simultaneously samples different directions of the short-range exchange field. The superconductor's critical temperature, ${T}_{C}$, is therefore expected to partially recover when the ferromagnet is in a multidomain state, as opposed to a single-domain state. Here, we discuss series of experiments performed with ferromagnet(Pt/Co)/spacer(IrMn and Pt)/superconductor(NbN) heterostructures. By tuning the various parameters in play, e.g., superconducting coherence length-to-thicknesses ratio, and domain sizes, we obtained up to 10% recovery of the superconducting critical temperature $\mathrm{\ensuremath{\Delta}}{T}_{C}/{T}_{C}$. This large-scale recovery made investigations possible. In particular, from the spacer thickness dependence of $\mathrm{\ensuremath{\Delta}}{T}_{C}/{T}_{C}$, it was possible to deduce the characteristic length for Cooper pair penetration in an IrMn antiferromagnet. This information is crucial for electronic transport, and up to now has been difficult to access experimentally for antiferromagnets.
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Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation N. Ivanovo, L. Terentieva, D. Sattarov, Yu. Proshin, M. G. Khusainov; The FM/S/FM Trilayer: Inhomogeneous π‐Phase Superconductivity. AIP Conf. Proc. 7 September 2006; 850 (1): 907–908. https://doi.org/10.1063/1.2354998 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search
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Abstract This chapter starts off with a discussion of the specifics of superconductivity in ultrasmall superconducting grains. The method of optimal fluctuations in the vicinity of Tc is then introduced, and applied to the study of the formation of superconducting drops in a system with quenched disorder or in strong magnetic fields. The exponential DOS tail in a superconductor with quenched disorder is calculated. Properties of Josephson coupled superconducting grains and drops are discussed. The XY-model for granular superconductor and the GL description of the granular superconductor are formulated. The broadening of superconducting transition by the quenched disorder is found. The final part of the chapter focuses on the specifics of the quantum phase transition in granular superconductors. It discusses Coulomb suppression of superconductivity in the array of tunnel coupled granules, properties of superconducting grains in the normal metal matrix, and phase transition in disordered superconducting film in strong magnetic field.
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Tetragonal crystal system
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There is strong evidence that magnetic interactions play a crucial role in the mechanism driving high-temperature superconductivity in cuprate superconductors. To investigate this further we have done neutron scattering experiments on the simplest high-temperature superconductor La(2-x)Sr(x)CuO(4) (LSCO) in an applied magnetic field. Below the superconducting transition temperature (Tc), the field penetrates the material via an array of normal state inclusions or vortices while phase coherent superconductivity characterized by zero resistance is suppressed to the lower field-dependent irreversibility temperature. The measurements described here were performed on underdoped LSCO (x=0.10), which develops static incommensurate order below Tc in zero field. Our results show that application of a magnetic field enhances this response without changing the onset temperature. For H=5T the field-induced signal saturates to three times the zero-field signal and phase coherent superconductivity is established within the antiferromagnetic phase.
Vortex state
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Buffer (optical fiber)
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Infrared (IR) and x-ray photoemission spectroscopy (XPS) studies have been made on heterogeneously iodine-doped polyphenylacetylene (PPA) polymer films. Similarities and differences between the doping processes (heterogeneous and homogeneous) are presented. Results point to a surface doping process in the heterogeneously doped films vs. a bulk process in the homogeneously doped materials (doped in solution). The counter anion moiety in the films appears to be the polyiodide I 5 − ion, as contrasted to the bulk powder (homogeneously doped) polymer in which the species of I 2 , I 3 − in the presence of a predominance of I 5 − ion coexist.
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