J. F. Carolan

Growth and properties of superconducting YBCO single crystals

Large, high quality YBa2Cu3O7-x (YBCO) single crystals have been grown by a flux method and characterized by low field magnetization, a−b plane resistivity, microwave surface resistance and heat capacity measurements. The crystals obtained are nearly free standing after crystal growth and are easily harvested. They have dimensions of up to 5 mm along the a-(b-) axis and up to 1 mm along the c-axis. After oxidation, the crystals show a superconducting transition at Tc=93.2 K with transition width, ΔTc, of < 0.25 K as determined by low field magnetization, a−b plane resistivity and heat capacity data. The heat capacity jump ΔCp of the superconducting transition is 6.9 mJ/(gK).

Site of the positive muon in YBa2Cu3O7

A combination of μSR and17O nuclear quadrupolar μLCR has been used to obtain detailed information on the muon site in YBa2Cu3O7. The rms magnitude of the nuclear dipolar fields in YBa2Cu3O7 enriched with 38%17O is about twice that in the natural16O sample. In addition the17O μLCR spectrum shows that the electric field gradient tensor at the oxygen closest to the muon is almost equal to that measured by NMR for the CuO2 plane sites O(2,3). These results suggest that the muon in fully oxygenated YBa2Cu3O7 is located at a single site 1.0 Å from an oxygen ion, probably O(2,3).

A planar method for patterning of high‐temperature superconducting films and multilayers

We present a novel technique for patterning high‐temperature superconducting (HTS) film and multilayer device structures. In the process an impurity ion (e.g., Si) is implanted into HTS films through a photoresist mask. The impurity ions convert the irradiated portion of the film into an insulating form by chemical reaction between the ions and the oxygen in the film, without altering the overall crystalline structure of the film. Removal of the photoresist results in a flat surface, which allows the epitaxial growth and implantation patterning of subsequent films so that a complete multilayer device structure can be fabricated. We show in detail the patterning process, as well as the properties of patterned and regrown films. Some simple device structures, such as a vertical contact and a crossover, are demonstrated.

Inhibition of superconductivity in Y‐Ba‐Cu‐O films by Si ion implantation

A method of converting an oxide Y‐Ba‐Cu‐O (YBCO) film from superconducting into insulating film is presented. With implanted Si ions, the film loses its electrical conductivity and diamagnetism while its crystalline structure is preserved. The process allows the growth of an epitaxial YBCO film on top of the inhibited area, thus providing an effective method of patterning high temperature superconducting multilayer structures.

Temperature dependence of the magnetic penetration depth in YBa2Cu3O7 measured by muon spin rotation

We report an improved measurement of the temperature dependence of the magnetic penetration depth in sintered YBa2Cu3O77 using muon spin rotation. The effective isotropic average of the magnetic penetration depth (λ) is estimated from the second moment of the field distribution in the vortex state in an external field of 15kG. The low temperature behaviour of λ is still consistent with an s-wave pairing mechanism although there are deviations from the conventional BCS-like behaviour for T/Tc > 0.2.

The superconducting glass transition in Y Ba2 Cu3 O7−δ

Abstract The electrical resistance and the d.c. magnetization of bulk sintered Y Ba2 Cu3 O7−δ were measured for magnetic fields, H, in therange 1 Oe to 5 kOe near the superconducting transition temperature. The onset temperature for hysteresis, T(H), determined from the resistance measurements was found to obey the relation H α [ 1 − T(H) T(O) ] γ with γ = 1.49 ±.04. The results are evidence for the existence of the superconducting glass state in this material and provide quantitative agreement with the Almeida-Thouless prediction of γ = 1.5.

Inhibition patterning of oxide superconducting films with Si ion implantation

A new method of inhibition patterning of oxide superconducting (YBCO) films is presented. With implanted Si ions, the YBCO film loses its electrical conductivity and diamagnetism, while its crystalline structure is preserved. The method allows the growth of a second epitaxial YBCO layer on top of the inhibited area, thus providing an effective method of patterning oxide superconductor multilayer structures. Micrometre-sized superconducting lines have been patterned by Si ion implantation with a photoresist mask. Both patterned structures and second-layer films have superconducting properties similar to those of pure YBCO films.

Magnetic ordering in YBa2Cu3Ox studied by μ+ spin rotation☆

YBa2Cu3Ox is known to be antiferromagnetic (AFM) for x ≲ 6.45 but the details of its sublattice magnetization(s) are still controversial. A zero-field μ+SR investigation of the x- and T-dependence of the local fields at several muon sites reveals sharp changes at 10K and 80K for an oriented powder sample with x ≈ 6.0, but other x ≈ 6.0 samples do not show the same features. The direction of the local field at one μ+ site is shown to be along the ĉ-axis. For x < 6.0 the samples still show local spin freezing up to 300K, but coherent AFM order is lost even at 3K.

Properties of Ca1−xSrxCuO2 infinite layer films grown by laser ablation deposition

Films of the infinite layer compound Ca1−xSrxCuO2 have been grown on SrTiO3 substrates by pulsed laser ablation deposition. The properties of the films depend strongly on the processing temperature. Between 650–700 °C the films are epitaxial with the c axis oriented normal to the surface of the substrates. The surfaces of the films are smooth, as indicated by scanning electron microscopy. Films processed at temperatures above 740 or below 600 °C are polycrystalline. X‐ray diffraction patterns show that the c‐axis lattice constant varies from 3.23 A for x=0.10, to 3.39 for x=0.66 and 3.43 A for x=0.90. Electrical measurements show the films to have a semiconducting behavior; no diamagnetic transition was observed in these films.

μ+ SR lineshape of oriented and unoriented high Tc superconductors

Abstract A new method of fitting the magnetic penetation depth from transverse field muo spi rotation (TF μSR) data is demonstrated with oriented and unoriented sintered powders and single crystals of high T c superconducting oxides.