Daniel Ariosa Dupont

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Texture characterization in thin films from standard powder x-ray diffraction (XRD) rely on the comparison between observed peak relative intensities with those of powder diffraction standards of the same compound, trough the so-called texture coefficient ...

In YBa2Cu3O6+x the tetragonal to orthorhombic transition occurs around x equals 0.3, followed by a continuum variation of lattice parameters. Hence both, the structural and superconducting properties, depend upon the oxygen content in CuO chains. Conversely, the epitaxial stress, exerted by the substrate on YBCO films, modified the lattice parameters, influencing the oxygen stability in the chains. The understanding of this mechanism is essential when growing epitaxial films for in-situ photoemission studie

We report on a distortion of Bi2Sr2CanCun+1 O6+2n+x (n = 0,1) single crystals, perpendicular to the CuO2 planes (the c-axis), for non-stoichiometric samples containing an excess of Bi. The distortion involves two parts: (a) symmetric displacements in the SrO and CuO2 planes along the c-axis, and (b) an antisymmetric longitudinal compressive wave. The latter is revealed by observing odd harmonics in the X-ray diffraction (XRD) data. Such odd harmonics are typically extinguished for the 14/mmm space group of

One of the intrinsic difficulties for in situ photoemission studies of high T-c oxide films is the surface volatility, especially the oxygen loss. In order to solve this problem, we have constructed a dedicated system for high T-c film surface studies, in particular for ARPES measurements. Here we briefly describe our pulsed laser deposition (PLD) system that is linked to the photoemission chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, and discuss crystallographic and electronic properties

Due to imperfect surfaces of most cuprate samples, almost all photoemission studies in the past decade were performed on Bi2Sr2CaCu2O8+x, even though a large fraction of other studies and electronic applications was reported for YBa2Cu3O7-delta (YBCO) family of superconducting compounds. In order to systematically study the gap parameter and the Fermi surface variation in high symmetry directions of YBCO and related oxide films we have constructed a new facility at the Wisconsin Synchrotron Radiation Center

We describe a new pulsed laser deposition (PLD) system that is linked to an angle-resolved photoemission (ARPES) chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, USA. We also discuss our first results on epitaxially grown YBa2Cu3O7-delta (YBCO) films. The core level photoemission data indicate that a Be-oxide layer is the dominant surface layer. We were not able to reproducibly detect a sharp fermi edge in the photoemission spectra and thus conclude that the surface layer is non-metallic, pro

We use a pulsed laser deposition (PLD) setup to grow ultra-thin films of high temperature superconductors (HTSC) and transfer them in-situ into a photoemission chamber. Photoemission measurements on such films allow us to study noncleavable materials, but can also give insights into aspects never measured before, like the influence of strain on the low energy electronic structure. Systematic studies of many different materials grown as films showed that Bi2Sr2CaCu2O8+x, Bi2Sr2Cu1O6+x, Bi2Sr2Ca2Cu3O10+x, and

We used pulsed laser deposition, with a Bi2Sr2CaCu2O8+x target, to grow films ranging from (1/4) to 10 unit cells thick. We studied these films, and reference Bi2Sr2CaCu2O8+x single crystal samples, using angle-integrated photoemission, core level photoemission, and x-ray diffraction. The data indicate that all films exhibit a metallic-like Fermi edge in the photoemission data. More strikingly, a structural phase transition occurs at a nominal Bi2Sr2CaCu2O8+x thickness of approximately one unit cell, conver

Since 1997 we systematically perform Direct ARPES (=DARPES) on in-situ grown, non-cleaved, ultra-thin (

We have observed the wavevector quantization in LaSrCuO films thinner than 12 unit cells grown on SrTiO3 substrates. Low energy dispersions were determined in situ for different photon energies by angle resolved photoemission spectroscopy. From the wavevec ...

We used a pump-probe technique to measure the transient change of optical reflectivity of both La2-xSrxCuO4, of various dopings, and slightly underdoped YBa2Cu3O7-x and NdBa2Cu3O7-x thin films. For the La2-xSrxCuO4 films, our data demonstrate the coexistence, in the superconducting state, of two coupled subsystems with different relaxation times and different contributions to the optical reflectivity. One subsystem is associated with the superconducting phase. By contrast. the data from YBa2Cu3O7-x, and NdB

Properties of ultra-thin films are different from their single crystal counterparts due to the presence of (substrate induced) strain, different degree and type of (growth induced) disorder and different average doping (distribution of oxygen vacancies, for example). Here we briefly summarize main results on ultra-thin (99 --> 1 unit cell (UC)) superconducting oxide films grown by laser ablation. Systematic studies show that BSCCO-2212, 2201, 2223, and LSCO-214 exhibit conductor-like Fermi edge, whereas mat

We report on X-ray photoemission of core levels, valence band studies using angle-integrated photoemission, and magnetization measurements of ruthenocuprate and SrRuO3 polycrystalline samples. The data indicate that the RuO2 planes are the source of the energetics of the magnetic ordering. We also find that adding hydrogen leads to changes in the many-body response on both the CuO2 and EuO planes.

We briefly summarize well established and the latest experimental results concerning the doping dependence of the so-called pseudogap (T*) and emphasize that surface related techniques, like ARPES or tunneling, give somewhat higher value of T* as compared to the bulk techniques, like specific heat. In the underdoped regime most theoretical models differ in extrapolating the T*-line to zero doping. As underdoped cuprates are rather inhomogeneous and the disorder plays an important role, the complete microsco

We have optimized laser ablation thin film deposition and transfer procedures within synchrotron vault, specifically to perform angle-integrated and angle-resolved photoemission spectroscopy (ARPES) on high-T-c and related films without cleaving the samples. However, the chain-containing phases like YBCO-123 easily loose surface oxygen and do not exhibit stable Fermi edge, hence are not suitable for ARPES studies. Direct in situ ARPES studies on strained LSCO-214 films show striking strain effects on the el

We report on x-ray photoemission and absorption measurements on ruthocuprate and SrRuO3 samples. The ruthocuprates include samples that are both weak ferromagnets and superconductors for part of the phase diagram. The results indicate that adding hydrogen changes the many-body response on the CuO2 planes. The results further indicate that ferromagnetic order alters the core level states. We discuss implications of these data.

Angle-resolved photoemission spectroscopy reveals very surprising strain-induced effects on the electronic band dispersion of epitaxial La2-xSrxCuO4-delta thin films. In strained films we measure a band that crosses the Fermi level (E-F) well before the Brillouin zone boundary. This is in contrast to the flat band reported in unstrained single crystals and in our unstrained films, as well as in contrast to the band flattening predicted by band structure calculations for in-plane compressive strain. In spite

We report on improved structural, crystallographic and electrical properties of epitaxial NdBa2Cu3O7-delta (NBCO) films grown on SrTiO3 by 'off-axis' pulsed laser deposition (PLD). Transport and XRD studies show that the c-axis-oriented epitaxial films, with critical temperatures of 90-92 K, are mono phase and single-crystalline. Furthermore, very smooth, almost outgrowth-free surfaces and crystal coherences of up to 0.8 mum (to our knowledge the best value ever reported for high-T-c films) were obtained.

We investigate the presence of secondary phases in La-doped Bi-2201 thin films grown by laser ablation. The cation ratios in the target material, the oxygen pressure, and the substrate temperature during the deposition are the main parameters determining t ...

We have measured two structurally similar superconducting systems, RuSr2GdCu2O8 and GdBa2Cu3O7 by means of high-resolution ac susceptibility. The real and the imaginary part of ac susceptibility of both bulk-ceramic and powdered samples have been studied down to the very small magnetic-field levels. We show that there are significant differences in the evolution of superconductivity in the two studied superconducting systems. In particular, we show that the superconducting transition in the grains in RuSr2G

Daniel Ariosa Dupont

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Texture vs morphology in ZnO nano-rods: On the x-ray diffraction characterization of electrochemically grown samples

Structural properties of strained YBa2Cu3O6+x superconducting films grown by pulsed laser deposition

Periodic c-axis modulation and crystallographic Fourier analysis of Bi2Sr2Cun+1O6+2n+x (n=0,1) single crystals with excess Bi

Surface optimization of RBa2Cu3O7-delta (R = Y, Nd) epitaxial high T-c films for in situ photoemission studies

Electronic properties of layered oxides: Pulsed laser deposition of YBCO films for in-situ studies by photoemission spectroscopy

Pulsed laser deposition for in-situ photoemission studies on YBa2Cu3O7-delta and related oxide films

Electronic properties of high temperature superconducting thin films grown by pulsed laser deposition

Structural phase transition in early growth of Bi2Sr2CaCu2O8+x films on SrTiO3 substrates

Direct angle resolved photoelectron spectroscopy (DARPES) on high-Tc films: doping, strains, Fermi surface topology and superconductivity

Fermi surface determination from wavevector quantization in LaSrCuO films

Evidence for two coupled subsystems in the superconducting state of La2-xSrxCuO4

Systematic studies of (magneto)transport, structural and electronic properties of ultra-thin films of high-T-c cuprates and related layered oxides

Electronic and magnetic properties of ruthenocuprates

On the doping variation of the pseudogap in high-T-c cuprates

Direct photoemission spectroscopy and electronic properties of in situ grown, strained high-T-c and related oxide films

Photoabsorption and core-level photoemission study of ruthocuprates

Strain and high temperature superconductivity: Unexpected results from direct electronic structure measurements in thin films

Improved structural properties and crystal coherence of superconducting NdBa2Cu3O7-delta films grown by pulsed laser ablation

Embedded polytypes in Bi2Sr2-xLaxCuO6 thin films grown by laser ablation

Superconducting transition in ruthenocuprate RuSr2GdCu2O8 viewed from the studies of the imaginary part of ac susceptibility