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We present a combined resonant soft X-ray reflectivity and electric transport study of LaAlO 3/SrTiO 3 field effect devices. The depth profiles with atomic layer resolution that are obtained from the resonant reflectivity reveal a pronounced temperature dependence of the two-dimensional electron liquid at the LaAlO 3/SrTiO 3 interface. At room temperature the corresponding electrons are located close to the interface, extending down to 4 unit cells into the SrTiO 3 substrate. Upon cooling, however, these interface electrons assume a bimodal depth distribution: They spread out deeper into the SrTiO 3 and split into two distinct parts, namely one close to the interface with a thickness of about 4 unit cells and another centered around 9 unit cells from the interface. The results are consistent with theoretical predictions based on oxygen vacancies at the surface of the LaAlO 3 film and support the notion of a complex interplay between structural and electronic degrees of freedom.

We have prepared a LaMn0.5Ga0.5O3 thin film deposited by Pulsed Laser Deposition on a LSAT subst rate and we have measured its transmittance in the visible and near UV range, from 300 to 10 K. The aim was to shed light on the orgin of the electronic bands in the LMO family through a comparison with the corresponding spectra collected previously on the parent compound. Two out of the four bands detected have been assigned to the intersite d-d transitions between Mn +3 ions. The other ones were ascribed to the p-d Mn-O charge-transfer transitions. We are thus led to a ”mixed” interpretation where both a Mott-Hubbard and a charge-transfer approach concur to interpret the electronic spectrum of those manganites.

In this work, the irreversible effects of an applied electric field on the magnetotransport properties of LaAlO3/SrTiO3 conducting interfaces are investigated, with focus on their multiband character. Samples of different types, namely with either crystalline or amorphous LaAlO3 overlayer, are studied. The two-band analysis highlights the similarity of the electronic properties of crystalline and amorphous interfaces, regardless much different carrier densities and mobilities. Furthermore, filling and depletion of the two bands follow very similar patterns, at least in qualitative terms, in the two types of samples. In agreement with previous works on crystalline interfaces, it is observed that an irreversible charge depletion takes place after application of a first positive back gate voltage step. Such charge depletion affects much more, in relative terms, the higher and three-dimensional dyz, dzx bands than the lower and bidimensional dxy, driving the system through the Lifshitz transition from two-band to single band behavior. The quantitative analysis of experimental data evidences the roles of disorder, apparent in the depletion regime, and temperature. Noteworthy, filling and depletion of the two bands follow very similar patterns in crystalline and amorphous samples, at least in qualitative terms, regardless much different carrier densities and mobilities.

We report on the transport properties of hybrid devices obtained by depositing graphene on a LaAlO3/SrTiO3 oxide junction hosting a 4 nm-deep 2-dimensional electron system. At low graphene-oxide inter-layer bias, the two electron systems are electrically isolated, despite their small spatial separation. A very efficient reciprocal gating of the two neighboring 2-dimensional systems is shown. A pronounced rectifying behavior is observed for larger bias values and ascribed to the interplay between electrostatic field-effects and tunneling across the LaAlO3 barrier. The relevance of these results in the context of strongly coupled bilayer systems is discussed. (C) 2016 Author(s).

By resonant inelastic x-ray scattering in the soft x-ray regime we probe the dynamical multiple-spin correlations in the antiferromagnetic cuprates La2CuO4 and CaCuO2. High resolution measurements at the copper L3 edge allow the clear observation of dispersing bimagnon excitations. Theory based on the ultrashort core-hole lifetime expansion fits the data on these coherent spin excitations without free parameters.

The effects of the order parameter symmetry and the interface grain boundary orientation on the transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ biepitaxial grain boundary junctions have been investigated. 45/spl deg/ [100] tilt and twist junctions on SrTiO/sub 3/ [110] and MgO [110] substrates by employing respectively MgO and SrTiO/sub 3/ as seed layers have been fabricated. More complex junctions by using CeO as seed layers have also been fabricated and analyzed. The analysis of experimental data points towards a predominant d-wave symmetry of the superconductive order parameter.

YBa(2)Cu(3)O(7-delta) (YBCO) grain boundaries characterized by a misalignment of the c-axes (45 degrees c-axis tilt or 45 degrees c-axis twist) have been obtained by employing a recently implemented biepitaxial technique. Junctions based on these grain boundaries exhibit good Josephson properties useful for applications. High values of the I(C)R(N) product and a Fraunhofer-like dependence of the critical current on the magnetic field, differently from traditional biepitaxial junctions, have been obtained. The correlation between transport properties and microstructure has been investigated by Transmission Electron Microscopy (TEM), which was also performed on previously measured junctions. The presence of atomically clean basal plane (BP) faced tilt boundaries, among other types of interfaces, has been shown. The possibility of selecting these kinds of boundaries by controlling film growth, and their possible advantages in terms of reproducibility and uniformity of the junction properties an discussed. The possibility of employing these junctions to explore the symmetry of the order parameter is also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.