Thin film synthesis and the influence of irradiation-induced defects on the superconductivity of La1.8Sr0.2CuO4

Thin superconducting films of La_1.8Sr_0.2CuO₄ have been prepared by magnetron sputter deposition and subsequent temperature treatment. The composition of the films has been determined by Rutherford backscattering and the structure by thin film X-ray diffraction. The onset of superconductivity was about 32 K and the midpoint near 28 K. Defect production in the films by He ion bombardment revealed a drasticT _c reduction with a sensitivity similar to that observed in the Chevrel phases. Oxygen implantation and subsequent annealing led to an enhancement of theT _c onset.     

Convolution effects in superconductive tunneling

The quasiparticle density of states (DOS) of superconductors can be obtained from tunneling spectroscopy. When the normal-state differential conductance varies on the voltage scale comparable to that of strong-coupling effects, the standard normalization rule to extract the DOS is invalid, and the DOS is related to the measured data via an integral equation. These effects are exemplified by studying the geometry effect on the DOS for simple BCS superconductors. We apply these considerations to UPd2Al3 tunnel data where the apparent strong-coupling effects, previously deduced by use of the normalization rule, can be quantitatively attributed to convolution effects.     

Pulsed electron-beam annealing of high-dose arsenic implanted silicon

The effects of pulsed electron-beam annealing of high-dose As implanted {111} Si single crystals has been studied. The depth distributions and lattice location of the As atoms were obtained using MeV⁴He⁺ backscattering and channeling technique. The implantation energy was 100 keV with a total dose of 3.5·10¹⁶/cm². Above the threshold energy of 0.9 J/cm² the single-crystal transition was observed with about 95% of the As atoms on substitutional lattice sites. This leads to an As concentration of 2·10²¹/cm³ which was demonstrated to be a metastable one.     

Electron tunneling into thin films of Y1Ba2Cu3O7

We have fabricated tunnel junctions on thin films of Y₁Ba₂Cu₃O₇ which were epitaxially grown by magnetron sputtering on (100) and on (110) oriented SrTiO₃ substrates. These junctions of the type Y₁Ba₂Cu₃O₇/barrier/Pb or In showed with high reproducibility in the conductance a gap-like structure with the maxima near±16mV. We supplied experimental arguments that this structure reflects properties of the quasi particle excitation spectrum of Y₁Ba₂Cu₃O₇. The gap-like structure was found to disappear atT _c mainly by weakening and not by a shift of the peaks to lower voltages.     

Superconductivity above 100 K in multi-phase Y−Ba−Cu−O

We report the synthesis, characterization and superconducting temperature of high-temperature superconducting Y_0.3Ba_0.7CuO₃, Y_0.4Ba_0.6CuO₃ and Y_1.2Ba_0.8CuO₄. The volume fraction of the superconducting phase is estimated to be of the order of 10%.HighT _c superconductivity withT _c -onsets up to 125 K (midpoint 102 K, zero resistance: 90 K) is observed in multi-phase Y–Ba–Cu–O oxygen defect compounds with the nominal composition of Y_1.2Ba_0.8CuO_4–y (0y0.4).     

Superconductivity at 40 K in La1.8Sr0.2CuO4

High-T _c superconductivity withT _c onsets up to 42 K (midpoint: 37 K, zero resistance: 34 K) is observed in X-rays homogeneous single phase La_1.8Sr_0.2CuO₄. The quarternary compounds La_2–x Ba _x CuO₄ and La_2–x Sr _x CuO₄ (0x0.3 for Ba and 0x<1 for Sr, depending on the heating conditions) are mixed-valence oxygen defect oxides, characterized by the presence of Cu²⁺ and Cu³⁺ simultaneously. These oxides have a tetragonal symmetry (space group:I 4/mmm) similar to that of K₂NiF₄. We report the synthesis, characterization, and superconducting properties of various high-temperature superconducting La–Ba–Cu–O and La–Sr–Cu–O compounds. Through the substitution of Sr for Ba in these oxygen defect compounds an increasing superconducting transition temperature onset from 28 K to 35 K for La_1.8Sr_0.1Ba_0.1CuO₄ was observed. A positive initial pressure coefficient ofdTc/dp=290 (mK/kbar) has been found for La_1.8Sr_0.2CuO₄ with a magnetic susceptibility change consistent with the 100% diamagnetic expectation value.     

Deposition of superconducting CeCoIn5 thin films by co-sputtering and evaporation

Thin superconducting films of CeCoIn₅ were prepared in situ by simultaneous thermal evaporation of indium and dc magnetic field assisted sputtering of planar metallic Ce and Co targets. To achieve an effective sputtering of the magnetic Co target a special geometry with two facing planar targets (Ce and Co) and magnetic field perpendicular to the targets was used. The stoichiometric (0 0 1)-oriented CeCoIn₅ films were grown on r-cut sapphire substrates with a high-rate of 100 nm/min. The temperature dependence of the electrical resistivity revealed the characteristic heavy-fermion behavior and a superconducting transition at about 2 K in agreement with the literature data for CeCoIn₅ bulk material and thin films.