Charge Density Wave and Superconducting Properties in Single Crystals of Lu5Ir4Si10

We measured the electrical resistivity from 2K up to 900K on high quality single crystals of Lu5Ir4Si10. A clear thermal hysteresis was found at the onset of the Charge Density Wave (CDW), evidencing the first order nature of the transition. When tantalum is included in the compound, the CDW is destroyed and the superconducting critical temperature is enhanced. Finally, we present specific heat and magnetic penetration depth in the Meissner state. We show that the superconducting properties are very close to a weak coupling BCS superconductor

Ferromagnetism in novel compounds of the R3Pt23Si11 series with heavy rare earth: Gd, Tb, Dy, Ho and Er

International audienceWe have synthesized new compounds of the R3Pt23Si11 series with R=Gd, Tb, Dy, Ho and Er, and studied their magnetic and thermodynamic properties. X-ray powder diffraction characterization confirms that all these compounds crystallize in the same face-centered cubic structure, space group Fm-3m, as Ce3Pt23Si11. They all present a ferromagnetic order at low temperatures. The Curie temperatures range between 42±1 K to 3.39±0.05 K for Gd3Pt23Si11 to Er3Pt23Si11 respectively. For all compounds the value of the spontaneous moment at 2 K is far below the value expected for the saturated moment of the R3+ ions, except for the Gd compound. The estimations of the magnetic entropy at TC remain smaller than the full entropy of the fundamental multiplet, Rln(2J + 1). Both reductions, of the moment and of the magnetic entropy, are ascribed to the crystal field effects. In the paramagnetic phase the thermal variation of the suceptibilities follow a Curie-Weiss law with Curie constants in good agreement with the theoretical value

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

Physical properties of the R3Pt23Si11 compounds with volatile rare earth: Sm, Eu, Tm and Yb

International audienceThe new R3Pt23Si11 series, where R is a rare earth, has been completed with the synthesis of three new compounds with volatile rare earth : R = Eu, Sm, and Tm. The studies of their physical properties have been performed along with those of the Yb3Pt23Si11 compound. The X-ray powder diffrac-tion patterns confirm that they all crystallize in the same face-centered cubic structure, space group F m - 3m, as the rest of the series. The refinements of the diffraction patterns show an anomalously high lattice parameter in Eu3Pt23Si11 and Yb3Pt23Si11, indicating a divalent valence state for Eu and Yb. This 2+ valence state for Eu and Yb ions is confirmed by the magnetic measurements. A ferromagnetic order is observed at Tc = 5.54±0.07 K and 10.12±0.07 K in Eu3Pt23Si11 and Sm3Pt23Si11 respectively. In Tm3Pt23Si11 no magnetic order is found down to 0.36 K while Yb3Pt23Si11 reveals a dia-magnetic behavior. At low temperatures the spontaneous moment, Ms , in Eu3Pt23Si11 is in agreement with a L=0, S=7/2 state for the Eu 2+ ion. On the contrary in Sm3Pt23Si11, Ms is far below the 0.714 µB expected for the saturated moment of the Sm 3+ in the J =7/2 ground state multiplet

Crystal growth and characterization of the ruthenate superconducting compound: Sr2RuO4

International audienceSr2RuO4 is a copper-free layered perovskite superconductor with the tetragonal K2NiF4-type structure. The precise nature of the pairing in the superconducting state of this material is still under debate. In this paper, we report about crystal growth and characterization of this compound. The crystals were grown by a floating zone technique using a light furnace equipped with double elliptical mirrors starting from off-stoichiometric Sr2RuO4. The crystals have been checked by X-ray diffraction and microanalysis. The superconducting properties were measured by AC-susceptibility, magnetization and specific heat. High crystalline quality centimetre-sized crystals have been grown and best crystals exhibit superconducting transitions at View the MathML source (typical dimensions : 4.5 mm diameter and 70 mm length with the (0 0 1) axis perpendicular to growth direction). The unconventional superconductors are characterized by a drastic impurity effect on the superconducting properties. We try to establish a correlation between the defect concentration and the physical properties of Sr2RuO4

Charge density wave and superconductivity competition in Lu5_5Ir4_4Si10_{10} : a proton irradiation study

Real-space modulated Charge Density Waves (CDW) are an ubiquituous feature in many families of superconductors. In particular, how CDW relates to superconductivity is an active and open question that has recently gathered much interest since CDWs have been discovered in many cuprates superconductors. Here we show that disorder induced by proton irradiation is a full-fledged tuning parameter that can bring essential information to answer this question as it affects CDW and superconductivity with different and unequivocal mechanisms. Specifically, in the model CDW superconductor Lu$_5$Ir$_4$Si$_{10}$ that develops a 1D CDW below 77\,K and s-wave superconductivity below 4\,K, we show that disorder enhances the superconducting critical temperature $T_\mathrm{c}$ and $H_\mathrm{c2}$ while it suppresses the CDW. Discussing how disorder affects both superconductivity and the CDW, we make a compelling case that superconductivity and CDW are competing for electronic density of states at the Fermi level in Lu$_5$Ir$_4$Si$_{10}$, and we reconcile the results obtained via the more common tuning parameters of pressure and doping. Owing to its prototypical, 1D, Peierls type CDW and the s-wave, weak-coupling nature of its superconductivity, this irradiation study of Lu$_5$Ir$_4$Si$_{10}$ provides the basis to understand and extend such studies to the more complex cases of density waves and superconductivity coexistence in heavy fermions, Fe-based or cuprates superconductors.Comment: 25 pages single column, 4 figures in main text + 3 figures in appendi

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

CHARACTERIZATION OF THE 105 K SUPERCONDUCTOR Tl2Ba2CaCu208 ("2212")

International audienceHomogeneous Tl1.8Ba2CaCu208 ceramics were synthesized by a novel route, starting from Tl2Ba205 precursors and using high gas pressures. This method allows tight control of thallium losses, resulting in dense, large-grained samples with sharp superconducting transitions above 105 K. Results of a characterization by X-ray diffraction, optical micrographs and micro-probe analysis are presented, together with selected physical properties