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Multi-orbital physics in quasi-two-dimensional electron gases (q2DEGs) triggers intriguing phenomena not observed in bulk materials, such as unconventional superconductivity and magnetism. Here, we investigate the mechanism of orbital selective switching of the spin-polarization in the oxide q2DEG formed at the (001) interface between the LaAlO3, EuTiO3 and SrTiO3 band insulators. By using density functional theory calculations, transport, magnetic and x-ray spectroscopy measurements, we find that the filling of titanium-bands with 3dxz/3dyz orbital character in the EuTiO3 layer and at the interface with SrTiO3 induces an antiferromagnetic to ferromagnetic switching of the exchange interaction between Eu-4f7 magnetic moments. The results explain the observation of the carrier density-dependent ferromagnetic correlations and anomalous Hall effect in this q2DEG, and demonstrate how combined theoretical and experimental approaches can lead to a deeper understanding of emerging electronic phases and serve as a guide for the materials design of advanced electronic applications. [ABSTRACT FROM AUTHOR]

We measure the transmittance of LaMnO (LMO) thin films in the spectral range from 10 000 to 38 000 cm as a function of temperature. The optical conductivity obtained from the transmittance data is decomposed into five Drude-Lorentz contributions: three of them show evident changes below the Néel temperature T $\simeq$ 140 K. We discuss the band assignment in the framework of the tight-binding and of the orbitally degenerate Hubbard models. Our results ascribe the overall low-frequency spectrum of LMO to charge-transfer mechanisms involving the t and e electrons of the Mn ions, without invoking the presence of excitonic contributions. This finding definitely promotes a Mott-Hubbard scenario for LMO and provides an estimate of the Hamiltonian parameters. [ABSTRACT FROM AUTHOR]

The colossal magnetoresistance (CMR) manganese oxides, have been the subject of intense studies. To elucidate the mechanisms at work in the ferromagnetic metallic state is essential for the comprehension of the M–I transition and the associated CMR effect. We present here comparison among resistivities behavior in Ca and Sr-doped manganite films ( x = 0.3) grown by different techniques and on several substrates allowing to analyze samples with different amounts of disorder. At low temperatures, a dominant T 2 term in the resistivity has generally been observed. Our analysis shows that for residual resistivity values larger than a critical one, there is a substantial deviation from the T 2-like behavior and that an unusual T 2.5 one is robust. This behavior supports the theoretical proposal of single magnon scattering in the presence of minority spin states localized by the disorder. In the high temperature insulating paramagnetic phase the resistivity shows the activated behavior characteristic of polaronic carriers. Finally in the whole range of temperatures the experimental data are found to be consistent with a phase separation scenario. [ABSTRACT FROM AUTHOR]

We have designed an experiment that could allow to investigate, on the same sample, the interplay between the morphological anisotropy of high critical temperature superconductors and the effects related to the order parameter symmetry. To this aim we have employed c-axis tilt biepitaxial grain boundary YBa2Cu3O 7 - δ Josephson junctions and measured the junction properties for different junction interface orientations. The results give evidence of the possibility to tune normal state resistance and critical current density of a Josephson junction almost independently of each other. We interpret the results of this experiment as an indication that Cooper pairs and quasi-particles transport properties may be ruled by different mechanisms. Measurements apparently give evidence of the possibility to determine to some extent the presence of “ π-loops” and “0” loops along the same grain boundary line. [ABSTRACT FROM AUTHOR]

YBCO step-edge junction d.c. SQUIDs have been realized by using the Inverted Cylindrical Magnetron Sputtering (ICMS) technique. This last represents a novel technology for high- T Josephson junctions (HTSC). Steps are obtained by standard ion milling procedure on LaAlO (100) substrates using Nb-masks patterned by reactive ion etching. Measurements of current vs. voltage, maximum d.c. Josephson current vs. magnetic field and SQUID voltage response measurements have been performed, also as a function of the temperature. Operating temperature as high as 77K has been achieved. At 4.2K the SQUIDs show a maximum voltage of flux transfer function ∂ V/∂ φ = 870μV/ Φ and a good periodicity of the V-ϕ modulation up to 20 Φ without any sign of hysteresis. The ratio between the step height ( h) and the film thickness ( d) seems to play a fundamental role in determining Josephson properties of the bridges, these conditions being more severe with respect to most of the data available in literature. [ABSTRACT FROM AUTHOR]

Superconducting thin films of the TlBaCaCuO family have been prepared through a combined approach of MOCVD and thallium vapour diffusion. A three-step process has been adopted involving i) the synthesis of Ba−Ca−Cu−O films by MOCVD using «second-generation» barium and calcium sources, ii) the hydrolysis of the fluoride phases by annealing in water vapour-saturated oxygen and iii) the annealing in the presence of a thallium source. Reproducible results, in terms of phase formation, are discussed depending on the different conditions of the preannealing process. The superconducting films consist predominantly of single-phase TlBaCaCuO(2223). Preferential orientation of the crystallite c-axes perpendicular to the substrate surface has been observed. The films exhibit superconducting onset temperatures of 115-120 K with zero resistance higher than 100 K. [ABSTRACT FROM AUTHOR]

Accurate measurements of the magnetic penetration depth λ of n-doped (NdCeCuO) and p-doped (YBaCuO) high-temperature superconductors using a microscopic resonator are reported. The temperature dependence λ( T) in NdCeCuO films shows that the electrodynamics of this cuprate is well described in the framework of the BCS theory, with a single-valued finite-gap ratio 2Δ/ K T ≈3.1 throughout the entire temperature range below T . In contrast, measurements of λ( T) in YBaCuO cannot be fitted to a BCS temperature dependence derived from a single energy gap. In the low-temperature region, a quadratic behaviour of the penetration depth is observed, instead of the usual exponential law. These peculiar features are discussed in the light of recent theoretical models predicting a different symmetry state for the high- T superconductors. [ABSTRACT FROM AUTHOR]