The physics of the superconducting state in two-dimensional (2D) electron systems is relevant to understanding the high-transition-temperature copper oxide superconductors and for the development of future superconductors based on interface electron systems. But it is not yet understood how fundamental superconducting parameters, such as the spectral density of states, change when these superconducting electron systems are depleted of charge carriers. Here we use tunnel spectroscopy with planar junctions to measure the behaviour of the electronic spectral density of states as a function of carrier density, clarifying this issue experimentally. We chose the conducting LaAlO3-SrTiO3 interface as the 2D superconductor, because this electron system can be tuned continuously with an electric gate field. We observed an energy gap of the order of 40 microelectronvolts in the density of states, whose shape is well described by the Bardeen-Cooper-Schrieffer superconducting gap function. In contrast to the dome-shaped dependence of the critical temperature, the gap increases with charge carrier depletion in both the underdoped region and the overdoped region. These results are analogous to the pseudogap behaviour of the high-transition-temperature copper oxide superconductors and imply that the smooth continuation of the superconducting gap into pseudogap-like behaviour could be a general property of 2D superconductivity.

We present a study of the lattice response to the compressive and tensile biaxial stress in

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The perovskite SrTiO3-LaAlO3 structure has advanced to a model system to investigate the rich electronic phenomena arising at polar oxide interfaces. Using first principles calculations and transport measurements we demonstrate that an additional SrTiO3 capping layer prevents atomic reconstruction at the LaAlO3 surface and triggers the electronic reconstruction at a significantly lower LaAlO3 film thickness than for the uncapped systems. Combined theoretical and experimental evidence (from magnetotransport and ultraviolet photoelectron spectroscopy) suggests two spatially separated sheets with electron and hole carriers, that are as close as 1 nm.

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Epitaxial La 0.67 Sr 0.33 MnO 3 ͑LSMO͒ ferromagnetic thin films were coherently grown on NdGaO 3 ͑NGO͒ substrates with different crystal orientations of the surface plane. On the ͑110͒ o -and ͑001͒ o -oriented substrates, the film grows in the ͑001͒ pc orientation, and on the ͑100͒ o -, ͑010͒ o -, and ͑112͒ o -oriented substrates the film is ͑011͒ pc oriented ͑we will use subindices o and pc for the orthorhombic and pseudocubic crystal structures, respectively͒. The lattice parameters and pseudocube angles of the deformed LSMO pseudocube have been determined from x-ray diffraction measurements. The in-plane magnetic easy and hard directions of these films have been determined from the dependence of the remnant magnetization on the angle of the in-plane applied field. For all substrate orientations there is a strong in-plane uniaxial magnetic anisotropy, determined by the crystal directions of the substrate surface. The easy and hard magnetic-anisotropy directions are explained consistently by the ͑bulk͒ inverse magnetostriction model, except for the film on NGO ͑112͒ o .

Supplementary Information: DOI 10.1002/adfm.201102763, Preventing the reconstruction of the polar discontinuity at oxide heterointerfaces Determination of the Curie temperature When comparing a set of La 0.67 Sr 0.33 MnO 3 (LSMO) samples, the Curie temperature (T C ) of the samples is an important figure of merit for the sample quality. Therefore, a reliable method to determine T C is required. Here, a method based on the analysis of the magnetization loops is proposed. Magnetization measurementsT C is the temperature above, which the spontaneous magnetization disappears. However, the magnetic signal of LSMO does not drop to zero at T C in most measurements, as typically a small background field is used. This background field is necessary as LSMO's magnetization is very weak with a coercivity, which approaches zero around T C . LSMO's spontaneous magnetization will therefore be divided into domains with different orientations and no net magnetization can be observed without the background field. Above T C , LSMO has a very

The mechanisms behind the threshold-voltage shift in organic transistors due to functionalizing of the gate dielectric with self-assembled monolayers (SAMs) are still under debate. We address the mechanisms by which SAMs determine the threshold voltage, by analyzing whether the threshold voltage depends on the gate-dielectric capacitance. We have investigated transistors based on five oxide thicknesses and two SAMs with rather diverse chemical properties, using the benchmark organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene. Unlike several previous studies, we have found that the dependence of the threshold voltage on the gate-dielectric capacitance is completely different for the two SAMs. In transistors with an alkyl SAM, the threshold voltage does not depend on the gate-dielectric capacitance and is determined mainly by the dipolar character of the SAM, whereas in transistors with a fluoroalkyl SAM the threshold voltages exhibit a linear dependence on the inverse of the gate-dielectric capacitance. Kelvin probe force microscopy measurements indicate this behavior is attributed to an electronic coupling between the fluoroalkyl SAM and the organic semiconductor.