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Superconductor Quantum Interference Devices (SQUIDs), because of their extreme sensitivity to magnetic fields and radiation, have found important applications in biomagnetism, non-destructive evaluation and geophysics. One problem in the application of high-Tc SQUIDs is their noise performance. Recently, considerable progress has been made in reducing the noise. To understand the underlying mechanism, it is important to identify the microstructural origin of the junction noise.In this work actual SQUIDs of good and poor noise performance are studied and compared by TEM. The devices were made by epitaxially growing YBa2Cu3O7-x (YBCO) films using laser ablation on 24° SrTiO3 bi-crystal substrates. The TEM samples were prepared by polishing and ion milling. The TEM observation was performed on a JEOL EM-4000EXII and a Hitachi H-9000 microscope.Observation shows that the YBCO films and the grain boundary junctions (GB J) in the low-noise devices are in good quality. The microstructure of the films and the boundaries in the films are shown in fig. 1 and 2.

To investigate the critical thickness of ferroelectric BaTiO3 (BTO) films, we fabricated fully strained SrRuO3∕BTO∕SrRuO3 heterostructures on SrTiO3 substrates by pulsed laser deposition with in situ reflection high-energy electron diffraction. We varied the BTO layer thickness from 3to30nm. By fabricating 10×10μm2 capacitors, we could observe polarization versus electric-field hysteresis loops, which demonstrate the existence of ferroelectricity in BTO layers thicker than 5nm. This observation provides an experimental upper bound of 5nm for the critical thickness. The BTO thickness-dependent scaling of the remanent polarization agrees with the predictions of recent first-principle simulations [J. Junquera and P. Ghosez, Nature 422, 506 (2003)].

Using a scanning microwave microscope (SMM), we have investigated the phase separation in a 30%La5∕8Sr3∕8MnO3(LSMO)+70%LuMnO3(LMO) polycrystalline pressed powder sample, in which the LSMO phase is a perovskite ferromagnetic metal while the LMO phase is a hexagonal ferroelectric insulator. When the electrical properties of the sample were imaged using our SMM, the sample showed a significant contrast between the metallic LSMO and the insulating LMO grains, indicating a clear phase separation between the two phases. The metallic phase identified by the SMM clearly showed a ferromagnetic signal when investigated by a magnetic force microscope (MFM), providing solid evidence that the metallic phase is indeed the ferromagnetic LSMO. In addition, we have noticed a slight difference between the images generated by SMM and MFM, and we believe that this is due to the different depth scales probed by the two microscopy techniques.

We have measured the mutual inductance signal of the superconducting transition in ultra-thin YBa 2 Cu 3 O 7 - Au bilayers. The samples consist of d S = 50 A of c -axis oriented YBa 2 Cu 3 O 7 , capped with initially d N = 50 A of Au. As d N is increased on each sample, no decrease in T c is observed, to within our experimental resolution. These results set an upper limit of ≤ 15 A on the proximity coupling range of YBa 2 Cu 3 O 7 , through Au.

We report the properties of SNS Josephson junctions based on YBCO in an edge geometry. Pseudo-cubic perovskite materials such as (CaSr)RuO 3 and (LaSr)CoO 3 , as well as the layered perovskite materials such as (LaSr) 2 CuO 4 , Co-doped YBCO, and Ca-doped YBCO, have been used as epitaxial barriers. We have observed interface resistances on the order of 10 -8 to 10 -7 Ωcm 2 in the case of the cubic perovskite barriers, and interface resistances smaller than 10 -10 Ωcm 2 in the case of the layered perovskite barrier materials. We found that the junctions with smaller interface resistance values behave close to predictions of proximity effect theory.

We have studied the voltage noise in a series of biepitaxial HTS junctions as a function of temperature and magnetic field. We find that the voltage-current characteristics of these junctions are in very good agreement with the thermally activated RSJ model over a wide range of temperature. We compare the temperature dependences of the noise due to critical current and resistance fluctuations.

We investigated the twin domains of LaAlO3 (001) substrate using a scanning microwave microscope (SMM). Since the SMM can image the local dielectric constant of a sample quantitatively, we can observe the difference of the dielectric constant in the twin domains. Especially the (110) domains were observed more clearly than (100) domains, we attribute this to the difference of the strain in the ferroelastic LaAlO3.

We describe a “bi-epitaxial” process to create 45 degree grain boundary Josephson junctions in YBa 2 Cu 3 O 7 . These bi-epitaxial grain boundary Josephson junctions are defined by standard photolithographic technique, and appear to be readily extended to integrated circuits. Some transport properties are reported and compared to other types of grain boundary Josephson junctions.

The superconducting properties of epitaxial YBa2Cu3O7−δ on yttria stabilized ZrO2 and LaAlO3 substrates depend on substrate‐film interactions. The reduction in Jc was observed. (AIP)

Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ films of thicknesses ranging from 500 AA to 5 mu m have been successfully made by the reactive magnetron sputtering technique. The effects of composition, annealing condition, and thickness of an epitaxial film on its orientation are discussed. films show anisotropic resistivities and critical-current densities that are orientation-dependent. >

We report results of the study of electron tunneling into thin films of the new high-${T}_{c}$ superconductor La-Sr-Cu-O. Both sandwich-type tunneling with a Pb counterelectrode and point-contact tunneling have been successfully achieved. The results show exceptionally large energy gaps in these materials (roughly 20, 30, and possibly even 60 mV), larger than previously obtained on bulk sintered powders. We interpret these results as due to large anisotropy in this material or due to the presence of a a very high-${T}_{c}$ layer near the surface of the films. The method of preparation of this new superconductor in thin film form is also discussed.

Measurements of the temperature dependence of the surface resistance R{sub s} and of the surface reactance X{sub s} at 148 GHz are reported for YBa2Cu3O(7-delta) and Y2Ba4Cu8O(16-delta) superconducting films with the c axis oriented perpendicular to the film's substrate. For low temperatures (T < {Tc}2) we find X{sub s}(T) - X{sub s}(O) = BT-sq and R{sub s}(T) - R{sub s}(O) = AT. The implications of these results are discussed.

The upper critical field ${H}_{c2}$ and fluctuation conductivity were measured for highly oriented thin films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$. The ${H}_{c2}$ results demonstrate the intrinsic anisotropy in this layered superconductor. The broadening of the resistive transition under fields is interpreted in terms of critical fluctuations. The fluctuation conductivity shows dimensional crossover as expected for quasi-two-dimensional material. Using this data we determine the intra- and interlayer coherence lengths ${\ensuremath{\xi}}_{c}$(0) and ${\ensuremath{\xi}}_{\mathrm{ab}}$(0), and discuss the dimensionality of the superconductivity in this material.

The new superconducting phase Y 2 Ba 4 Cu 8 O 16− x in epitaxially grown thin films is compared to the newly discovered Bi 4 Ca 2 Sr 4 Cu 4 O 16+ x structure. Properties of Y 2 Ba 4 Cu 8 O 16− x are compared to those of Bi 4 Ca 2 Sr 4 Cu 4 O 16+ x . An analogy between the structure of those two materials is drawn and their properties are discussed.

Detailed examination of a well-ordered, high-${T}_{c}$ ${\mathrm{Y}}_{2}$${\mathrm{Ba}}_{4}$${\mathrm{Cu}}_{8}$${\mathrm{O}}_{16}$ (2:4:8) oriented thin-film sample revealed directly that the three crystallographic axes were unequal in length. Each layer of this high-${T}_{c}$ superconductor, like the closely related superconducting $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ (1:2:3) phase, has structural anisotropy in the $a\ensuremath{-}b$ plane. The difference between $a$ (3.859 \ifmmode\pm\else\textpm\fi{} 0.002 \AA{}) and $b$ (3.874 \ifmmode\pm\else\textpm\fi{} 0.002 \AA{}) in 2:4:8 is significantly smaller than in 1:2:3, so many associated strains such as those occurring during oxidation or epitaxial growth will also be smaller. Well-ordered, high-${T}_{c}$ thin films of 2:4:8 using Er in place of Y have been produced. By comparing the x-ray-diffraction patterns of the Y and Er 2:4:8 samples, a one-dimensional electron density map has been produced directly, without structure refinement. The result demonstrates that relative to the 1:2:3 structure, 2:4:8 contains an additional -CuO- layer. Together, the results indicate, without appeal to indirect chemical analogy, that 2:4:8 contains double -CuO- layers with interlayer vacancy ordering.

An ordered defect structure in superconducting Y-Ba-Cu-O thin films has been characterized by both x-ray diffraction and transmission electron microscopy. The defect structure, which is observed growing epitaxially within the grains of normal $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ structure, has the diffraction characteristics of a distinct phase whose volume fraction can be correlated with changes in film composition. The diffraction characteristics are consistent with an orthorhombic unit cell ($a\ensuremath{\cong}b=3.86$ \AA{}, $c=27.19$ \AA{}) with space group Ammm. These are the characteristics to be expected from a structure in which extra copper-oxygen layers create fault planes, which are inserted at every unit cell in the parent $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ structure. The composition expected for the pure phase is ${\mathrm{Y}}_{2}{\mathrm{Ba}}_{4}{\mathrm{Cu}}_{8}{\mathrm{O}}_{20\ensuremath{-}x}$. Preliminary transport measurements on films containing this extra phase are characterized by lower normal-state resistances and a lower Hall constant.

Microstructural characteristics of YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films on SrTiO/sub 3/ have an important influence on their physical properties. Four-axis X-ray diffraction methods have been used to characterize textured and nontextured phases in several YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films deposited on single-crystal SrTiO/sub 3/. The type of epitaxial orientation of a- and c-axis textured films has been analyzed by tilting the specimen and observing the distribution of YBa/sub 2/Cu/sub 3/O/sub 7- delta /

The optical anisotropy of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ in the 0.08--5.6 eV region is investigated by polarized reflectance measurements on single crystals, and by transmittance, reflectance, and ellipsometric measurements on oriented thin films. In the visible--near-uv spectral region the anisotropy is relatively mild, but a huge anisotropy is observed in the infrared. Here, the reflectance increases with decreasing frequency for both polraizations, consistent with metallic conductance both parallel and perpendicular to the ab plane. The c-axis plasma frequency is strikingly low, but there is strong damping which could originate from a continuum of low-energy interband transitions.

The new high-${T}_{c}$ superconductor YBaCuO was prepared and characterized. Measurements were performed to determine the superconducting and magnetic properties of the samples. Onset of superconductivity was found above 90 K. Antiferromagnetism was also observed, probably associated with the nonsuperconducting pairs of the samples. Modest critical current density as well as large upper critical fields were inferred from the data.

High Tc superconductors exhibit significant flux motion due to a thermally activated creep process. The motion of the fluxoids dissipates energy. This dissipation causes a broadening of the resistive transition below Tc in a magnetic field as well as a logarithmic decay of the diamagnetic shielding moment in time. From the detailed structure of the broadened transition, empirical parameters are derived. The pinning strength is highly anisotropic, reflecting the anisotropy of the coherence length. Implications of an extraordinarily low activation energy are also addressed.

Raman spectra of YBa2 Cu3 O7 excited by different lines of Ar and Kr lasers have been studied. It was found that significant changes in relative intensity of phonon lines occurred in the spectra when the excitation frequency was shifted from the red into the blue region of the spectrum. The enhancement of high‐frequency phonons, which involves stretching of CuO bonds, was attributed to resonance with an interband transition in YBa2 Cu3 O7 .

Thin films of the high‐temperature superconductor DyBa2Cu3O7−x have been grown on SrTiO3 substrates using molecular beam epitaxy techniques. Reflection high‐energy electron diffraction patterns observed during deposition indicate incomplete oxidation of copper and growth of oriented metallic copper microcrystals in a matrix of amorphous barium and dysprosium oxides. After post‐growth anneal the films exhibited sharp superconducting transitions with zero resistance observed as high as 89 K and critical current densities of 4.8×105 A/cm2 at 4.2 K and 3.9×104 A/cm2 at 77 K.

Optical transmission and reflection spectra (mid IR through uv) and Raman spectra of superior-quality 90-, 180-, 400-, and 1000-nm-thick superconducting Y-Ba-Cu-O films are reported. Characteristic excitonic bands, and in particular the absorption band at \ensuremath{\simeq}0.37 eV reported earlier, are not observed. It therefore seems unlikely that the high-${T}_{c}$ superconductivity in cuprates could arise from exciton-mediated electron pairing.

We report results of a study of electron tunneling into bulk samples of the new high-${T}_{c}$ superconductor Y-Ba-Cu-O using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 2\ensuremath{\Delta}=100 meV), implying 2\ensuremath{\Delta}/${k}_{C}$${T}_{c}$\ensuremath{\sim}13. Similar values were found previously by us for La-Sr-Cu-O. We also see Structure in the I-V curves similar to that seen in La-Sr-Cu-O. On the basis of the asymmetries observed in the I-V characteristics, we believe that the natural tunneling barrier on this material is of the Schottky type.

We report our experimental results of the surface chemistry and the electronic structure of YBa2Cu307_δthin film by photoemission study. An experimental technique has been successfully used to clean superconducting thin films for photoemission experiments, while still preserving the superconducting properties of the films. The photoemission spectra obtained are consistent with our earlier results from bulk ceramic samples. This technique is then applied to study the surface chemistry of thin films under different annealing conditions. The films which have been ex situ post annealed and the films which have not been ex situ post annealed have been studied and compared. It is found that the oxidation of copper in the film strongly depends on the history of the thermal treatment of the film. On the other hand, Ba seems very stable in its doubly ionized state under all annealing conditions.

Epitaxial YBa2Cu3O7 (YBCO) films were grown on r‐plane A12O3 {1102} by laser ablation. X‐ray diffraction shows that films are epitaxial with the c‐axis perpendicular to the substrate and the a or b axes parallel to (2201), although the full width at half maximum of the rocking curve is larger compared to those of epitaxial films on SrTiO3. The critical temperatures (zero resistance) are between 85 K and 88 K with transition widths between 0.5 K and 3 K. The 300 K resistivity of 250 μΩextrapolates to zero at zero temperature and the critical current is as high as 5 x 106 A/cm2 at 4.2 K according to magnetization hysteresis measurements. Surface resistance data shows that 2000 Å thick epitaxial films on {1102} have about 1 mΩ at 13 GHz at 4.2 K.

Post-annealed thin films comprised of mixed YBa2Cu3O7-x (123) and Y2Ba4Cu8O16 (248) phases with both faulted and unfaulted microstructures have been characterized by planar and cross-section transmission electron microscopy. The influence of 248-type faults on the 123 structure, possible mechanisms for the higher Tc's of faulted films, and observations of a fourfold ordered structure are discussed.

We report on ferroelectric field effect experiments in epitaxial oxide heterostructures consisting of the ferroelectric oxide Pb(Zr,Ti)O3 and the metallic oxides GdBa2Cu3O7 and SrRuO3. To perform the experiments, we used conventional capacitor structures, as well as a scanning probe approach that allows one to control the local ferroelectric polarization without the use of permanent electrical contacts. In the case of the scanning probe approach, nanometer scale control of the ferroelectric domain structure can be achieved over large areas of up to 2500 micrometer2. Nonvolatile, reversible electronic nanofeatures were written in Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures by switching the local polarization field of the ferroelectric layer, inducing a field effect in the thin (30 angstrom) SrRuO3 layer that changes its sheet resistance by 7%. This doping technique permits one to write reversible, nonvolatile electronic structures without requiring traditional lithographic processing or permanent electrical contacts.

We have experimentally investigated the density of states (DOS) in Nb/Ni (S/F) bilayers as a function of Ni thickness, d(F). Our thinnest samples show the usual DOS peak at +/- Delta(0), whereas intermediate-thickness samples have an anomalous "double-peak" structure. For thicker samples (d(F) > or =3.5 nm), we see an inverted DOS, which has previously only been reported in superconductor or weak-ferromagnet structures. We analyze the data using the self-consistent nonlinear Usadel equation and find that we are able to quantitatively fit the features at +/- Delta(0) -- in particular the thickness at which the inversion occurs -- only if we include a large amount of spin-orbit scattering in the model. Interestingly, we are unable to reproduce the subgap structure through the addition of any parameter(s). Therefore, the observed anomalous subgap structure represents new physics beyond that contained in the present Usadel theory.

We have grown thin, highly oriented, polycrystalline DyBa2Cu3O7−x films using molecular‐beam epitaxy (MBE) techniques that show the onset of superconductivity at temperatures above 90 K and complete transitions at temperatures as high as 87 K. These films have critical current densities as high as 5×105 A/cm2 at 4.2 K. Films were grown in a modified Varian 360 MBE machine using effusion sources containing the metal constituents, along with a gaseous oxygen source. The early stages of deposition were monitored with reflection high‐energy electron diffraction (RHEED). The best films were obtained on SrTiO3 substrates at substrate temperatures of 600–750 °C. At these temperatures, the initial stage of growth is dominated by epitaxy of copper islands. At lower temperatures, the growth is amorphous, while at higher temperatures, copper may not be incorporated into the film. Copper incorporation is also affected by oxygen flux. In all cases, the films are semiconducting or insulating as grown, and become superc...