Cathodoluminescence microscopy of superconducting and non-superconducting Tl2Ba2CuO6+x polycrystals

International audienceLuminescence properties of Tl2Ba2CuO6+x samples with different superconducting transition temperatures have been studied by cathodoluminescence (CL) in the scanning electron microscope. Independent of the crystal structure, tetragonal or orthorhombic, the CL spectra show two resolved bands at about 430 nm (2.9 eV) and 540 nm (2.3 eV), respectively. The results show that the 2.3 eV emission is related to oxygen content and is more intense in low-oxygen content superconducting samples. It is proposed that this band is related to a complex center involving oxygen vacancies. A comparison of spectra from Tl2Ba2CuO6+x and from precursors used in the synthesis (CuOx, Tl2Ba205) has been carried out

Crystal growth, structure and ferromagnetic properties of a Ce3Pt23Si11 single crystal

A high-quality single crystal of Ce3Pt23Si11 has been grown using the Czochralski method. The crystal structure is presented and the chemical composition has been checked using an electron microprobe analyzer. Measurements of the electrical resistivity and magnetic susceptibility performed at low temperature show a ferromagnetic transition at Tc = 0.44 K.Comment: 12 pages, 9 figure

Disorder raises the critical temperature of a cuprate superconductor

With the discovery of charge density waves (CDW) in most members of the cuprate high temperature superconductors, the interplay between superconductivity and CDW has become a key point in the debate on the origin of high temperature superconductivity. Some experiments in cuprates point toward a CDW state competing with superconductivity, but others raise the possibility of a CDW-superconductivity intertwined order, or more elusive pair-density wave (PDW). Here we have used proton irradiation to induce disorder in crystals of La$_{1.875}$Ba$_{0.125}$CuO$_4$ and observed a striking 50% increase of $T_\mathrm{c}$ accompanied by a suppression of the CDW. This is in clear contradiction with the behaviour expected of a d-wave superconductor for which both magnetic and non-magnetic defects should suppress $T_\mathrm{c}$. Our results thus make an unambiguous case for the strong detrimental effect of the CDW on bulk superconductivity in La$_{1.875}$Ba$_{0.125}$CuO$_4$. Using tunnel diode oscillator (TDO) measurements, we find evidence for dynamic layer decoupling in PDW phase. Our results establish irradiation-induced disorder as a particularly relevant tuning parameter for the many families of superconductors with coexisting density waves, which we demonstrate on superconductors such as the dichalcogenides and Lu$_5$Ir$_4$Si$_{10}$.Comment: 10 pages, 7 figure

Paramagnetic gold in a highly disordered Au-Ni-O alloy

Magnetic materials are usually classified into a distinct category such as diamagnets, paramagnets or ferromagnets. The enormous progress in materials science allows one nowadays, however, to change the magnetic nature of an element in a material. Gold, in bulk form, is traditionally a diamagnet. But in a ferromagnetic environment, it can adopt an induced ferromagnetic moment. Moreover, the growth of gold under certain conditions may lead to a spontaneous ferromagnetic or paramagnetic response. Here, we report on paramagnetic gold in a highly disordered Au–Ni–O alloy and focus on the unusual magnetic response. Such materials are mainly considered for plasmonic applications. Thin films containing Au, Ni and NiO are fabricated by co-deposition of Ni and Au in a medium vacuum of 2 × 10−2 mbar. As a result, Au is in a fully disordered state forming in some cases isolated nanocrystallites of up to 4 nm in diameter as revealed by high resolution transmission electron microscopy. The disorder and the environment, which is rich in oxygen, lead to remarkable magnetic properties of Au: an induced ferromagnetic and a paramagnetic state. This can be proven by measuring the x-ray magnetic circular dichroism. Our experiments show a way to establish and monitor Au paramagnetism in alloys

Lu5Ir4Si10 whiskers : morphologies, structure cristalline, mosaïcité, supraconductivité et onde de densité de charge

National audienceParmi la famille très riche de composés intermétalliques R5Ir4Si10 (R=terre-rare), la phase Lu5Ir4Si10 est supraconductrice en dessous de 4K et présente une transition liée à une onde de densité de charge à 80K [1]. Des cristaux en forme d'aiguilles ou whiskers ont été obtenus. Les conditions de synthèses sont présentées ainsi qu'une observation détaillée de leur taille et morphologie, obtenue au microscope électronique à balayage [2]. Des analyses par diffraction de rayons X ont confirmé que ces aiguilles cristallisaient sous la même structure quadratique P4/mbm que les cristaux massifs. Les paramètres de mailles a = 12.484(1) Å et c = 4.190(2) Å sont comparables à ceux de la littérature [3]. A l'aide d'un diffractomètre 4-cercles, nous avons trouvé que les aiguilles poussent selon l'axe c et que les faces latérales sont orientées selon la direction [110]. La mosaïcité de ces cristaux a été mesurée à l'ESRF, ligne ID27. Elle est inférieure à 0.15° le long de l'axe c. Enfin, des mesures de résistivité électriques sont détaillées. Elles confirment l'excellente qualité de ces cristaux

Cathodoluminescence microscopy of superconducting and non-superconducting Tl_2Ba_2CuO_(6+ δ) polycrystals

Luminescence properties of Tl_2Ba_2CuO_(6+ δ) samples with different superconducting transition temperatures have been studied by cathodoluminescence (CL) in the scanning electron microscope. Independent of the crystal structure, tetragonal or orthorhombic, the Cl spectra show two resolved bands at about 430 nm (2.9 eV) and 540 nm (2.3 eV), respectively. The results show that the 2.3 eV emission is related to oxygen content and is more intense in low-oxygen content superconducting samples. It is proposed that this band is related to a complex center involving oxygen vacancies. A comparison of spectra from Tl_2Ba_2CuO_(6+ δ) and from precursors used in the synthesis (CuO_x, Tl_2Ba_2O_5) has been carried out

Elastic anomalies at the first order transition in Lu5Ir4Si10

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Characterization of tetragonal Tl_2Ba_2Cu_1O_(6+δ) by cathodoluminescence microscopy

Superconducting Tl_2Ba_2Cu_1O(6+δ) ceramics shows two broad luminescence bands centered at 430 nm (2.9 eV) and 530 nm (2.3 eV) wich can not be related to impurity phases. The intensity of the bands is inhomogeneously distributed in the sample and there is a relation between regions of different intensities with the grains observed in the scanning electron microscope. Relationship of cathodoluminescence contrast with oxygen content distribution is discussed