R. Di Capua

Structural and Electronic Reconstructions at the LaAlO3/SrTiO3Interface

A full understanding of the mechanism of the formation of a two-dimensional electron gas (2DEG) at the interface between insulating LaAlO3 (LAO) thin films and bulk SrTiO3 (STO) crystals is a prerequisite for the full exploitation of this class of materials. Here, by using a combination of advanced X-ray synchrotron-based spectroscopic and structural measurements, it is shown that a structural and electronic reconstruction of the interface occurs before the realization of the 2DEG.

Emergence of coherence in the charge-density wave state of 2H-NbSe2

A charge-density wave (CDW) state has a broken symmetry described by a complex order parameter with an amplitude and a phase. The conventional view, based on clean, weak-coupling systems, is that a finite amplitude and long-range phase coherence set in simultaneously at the CDW transition temperature Tcdw. Here we investigate, using photoemission, X-ray scattering and scanning tunnelling microscopy, the canonical CDW compound 2H-NbSe2 intercalated with Mn and Co, and show that the conventional view is untenable. We find that, either at high temperature or at large intercalation, CDW order becomes short-ranged with a well-defined amplitude, which has impacts on the electronic dispersion, giving rise to an energy gap. The phase transition at Tcdw marks the onset of long-range order with global phase coherence, leading to sharp electronic excitations. Our observations emphasize the importance of phase fluctuations in strongly coupled CDW systems and provide insights into the significance of phase incoherence in ‘pseudogap’ states.

Critical currents of MgB 2 thin films deposited in situ by sputtering

We have measured the temperature and magnetic field dependencies of the critical current density J c (H,T) in MgB 2 thin films, in situ deposited by sputtering. Three-dimensional point like normal core pinning was evidenced by measurements of the magnetic dependence of the pinning forces independently from the superconducting and structural quality of the investigated films. The analysis of the experimental data in terms of the collective pinning model has pointed out the presence of a crossover magnetic field from a single vortex to a small vortex bundle pinning regime. A ΔT c pinning mechanism, i.e., a pinning associated with spatial fluctuations of the transition temperature, has been evidenced by the temperature dependence of this crossover field, in agreement with previous observations performed on MgB 2 bulk materials.

Ti- and Sr-rich surfaces of SrTiO3 studied by grazing incidence x-ray diffraction

The structure of SrTiO3 (100) (STO) single crystal surfaces has been investigated by grazing incidence x-ray diffraction. The authors found that chemically etched STO is composed ∼75% of an ideal TiO2 surface layer and ∼25% of SrO and it is very stable when annealed in ultrahigh vacuum or in O2 at high temperatures. A monolayer of SrO, epitaxially grown by pulsed laser deposition, is found to cover only a fraction of the TiO2 layers and exhibits a 2×2 reconstruction with strong structural changes after annealing in conditions typically used for the deposition of oxides.

In situ investigation of the early stage of TiO2 epitaxy on (001) SrTiO3

We report on a systematic study of the growth of epitaxial TiO(2) films deposited by pulsed laser deposition on Ti-terminated SrTiO(3) (001) single crystals. By using in situ reflection high energy electron diffraction, low energy electron diffraction, x-ray photoemission spectroscopy, and scanning probe microscopy, we show that the stabilization of the anatase (001) phase is preceded by the growth of a few nanometers thick pseudomorphic Sr(x)TiO(2+y) (x, y < 1) intermediate layer. The data demonstrate that the formation of this intermediate phase is related to the activation of a long range Sr migration from the SrTiO(3) substrate into the film. Our results enrich the phase diagram of the Sr-Ti-O system under epitaxial strain opening a route for the study of the electronic and dielectric properties of the reported Sr-deficient SrTiO(3) phase.

Role of interband scattering in neutron irradiated MgB2 thin films by scanning tunneling spectroscopy measurements

A series of

Direct observation of spectroscopic inhomogeneities on La0.7Sr0.3MnO3 thin films by scanning tunnelling spectroscopy

\mathrm{Mg}{\mathrm{B}}_{2}

In situ sputtering growth and characterization of MgB/sub 2/ films for microwave applications

thin films systematically disordered by neutron irradiation have been studied by scanning tunneling spectroscopy. The

Surface impedance of R1(NdxBa2−x)Cu3O7−δ (R=Nd, Y) thin films

c

Tunable spin polarization and superconductivity in engineered oxide interfaces.

-axis orientation of the films allowed a reliable determination of the local density of states of the