YBa2Cu3O7-delta (YBCO) has favorable macroscopic superconducting properties of Tc up to 93 K and Hc2 up to 150 T. However, its nanoscale electronic structure remains mysterious because bulk-like electronic properties are not preserved near the surface of cleaved samples for easy access by local or surface-sensitive probes. It has been hypothesized that Ca-doping at the Y site could induce an alternate cleavage plane that mitigates this issue. We use scanning tunneling microscopy (STM) to study both Ca-free and 10% Ca-doped YBCO . We provide experimental evidence, supported by density functional theory (DFT) calculations, that the Ca-doped samples do indeed cleave on an alternate plane, yielding a spatially disordered partial (Y, Ca) surface. On this surface, we image a superconducting gap with an average value of 26 meV +/- 4 meV and characteristic length scale of around 1 nm, similar to Bi-based high-Tc cuprates, and the first map of gap inhomogeneity in YBCO.

We present the results of x-ray diffraction, electrical resistivity, and ac magnetic susceptibility measurements on specimens of the "11"-structure superconductor Fe1+epsilon Te0.50Se0.50 (0 <= epsilon <= 0.15). Samples were initially either sintered in sealed quartz tubes or melted in a zirconium-gettered arc furnace. Sintered samples were fired two to three times at temperatures of 425 degrees C, 600 degrees C, or 675 degrees C, while arc-melted samples were studied both as-melted and after annealing at 650 degrees C. X-ray diffraction data show a predominant PbO-type tetragonal phase, with a secondary hexagonal NiAs-type phase; for sintered specimens annealed at 600 degrees C, the secondary phase decreases as e increases over the range 0 <= epsilon <= 0.10, with the composition Fe1.10Te0.5Se0.5 exhibiting x-ray phase purity. A higher annealing temperature of 675 degrees C provided such tetragonal phase purity at the composition Fe1.05Te0.5Se0.5. The resistive superconducting transition temperature T-c was nearly independent of the iron concentration 1+epsilon, suggesting a single superconducting phase, while the magnetic screening fraction varied greatly with concentration and conditions, peaking at epsilon = 0.07, indicating that the amount of superconducting phase is strongly dependent on conditions. We propose that the behaviour can also be viewed in terms of an electron-doped, chalcogen-deficient stoichiometry.

We report the effects of oxygen pressure during growth (PO2) on the electronic and magnetic properties of PrAlO3 films grown on TiO2-terminated SrTiO3 substrates. Resistivity measurements show an increase in the sheet resistance as PO2 is increased. The saturation of the sheet resistance down to 0.3 K is consistent with Kondo theory for PO2⩾10−5 torr. Resistivity data fits indicate Kondo temperatures of 16–18 K. For the 10−4 sample, we measured a moderate positive magnetoresistance (MR) due to a strong spin–orbit (SO) interaction at low magnetic fields that evolves into a larger negative MR at high fields due to the Kondo effect. Analysis of the MR data permitted the extraction of the SO interaction critical field for the PO2=10−5 torr interface (HSO=1.25 T). We observed high positive MR for the least oxygenated sample, where a fraction of the n-type carriers are derived from oxygen vacancies and possible cation interdiffusion; for this 6×10−6 torr sample, Hall effect data indicate a thick conducting layer. Its extremely high MR (∼400%) is attributed to classical behavior due to a distribution of mobilities.

We have investigated the effect of oxygen pressure during growth ( P O2 ) on the electronic and magnetic properties of PrAlO 3 films grown on TiO 2 -terminated SrTiO 3 substrates. The films are smooth, with flat terraces. Resistivity measurements show an increase in the sheet resistance as P O2 is increased from 10 –3 to 10 –4 torr, with an usual peak as a function of temperature for the sample grown in higher oxygen pressure. We measured a moderate positive magnetoresistance (MR) at low magnetic fields that evolves into a larger negative MR at high fields, for both P O2 samples. Hall effect data exhibit a complex temperature dependence that suggests a compensated carrier density. We observe behavior consistent with two different types of carriers at each of the two different interfaces.

We report pulsed laser deposition (PLD) synthesis of epitaxial and polycrystalline monoclinic bismuth vanadate (BiVO4, BVO) thin films. X-ray diffraction (XRD), atomic force microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were used to characterize the samples. Epitaxial, c-axis oriented growth was achieved using single crystal yttria-stabilized zirconia (100), a substrate temperature of 575–600 °C, and an oxygen pressure of 7.8 mTorr. The volatility of Bi necessitated a large excess (Bi:V = ∼6:1) of this element in the ceramic targets to obtain stoichiometric films. XRD confirmed a BVO (001)||YSZ (001) and BVO [100]||YSZ [100] epitaxial relationship. Film growth was 3-D, and the morphology was discontinuous, consisting of irregular, smooth grains. Additionally, dense, continuous polycrystalline films were deposited on fluorine-doped tin oxide (FTO) on glass substrates at room temperature with stoichiometric targets and postdeposition annealing in air. Evaluation of these samples as photoanodes yielded photocurrents of ∼0.15 and ∼0.05 mA cm–2 at 1.23 V vs RHE under backside AM1.5G illumination with and without a hole scavenger (Na2SO3), respectively. We argue that the photocurrents are due to the high oxygen content inherent in the PLD process and suggest that these continuous films may be well-suited to investigating oxygen-related defects in BVO.

Position-dependent force-detected NMR measurements on a 25×15×7 μm3 single crystal of ammonium sulfate (NH4)2SO4 were performed at room temperature in a sample-on-oscillator configuration. Force signals were detected with 12 μm resolution in a one-dimensional scan. Measurements of NMR relaxation times T2* = 1.5 ± 0.3 μs, T2 = 44 ± 2 μs, and T1 = 5.6 ± 0.7 s were obtained in an 8-T magnetic field, revealing an unexpected frequency-dependent fluctuation spectrum at room temperature.