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.

Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials' engineering tool in today's semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO3 at the interface between LaAlO3 and SrTiO3 oxides. Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO3 layer (TFM = 6-8 K) and is due to the exchange interaction between the magnetic moments of Eu-4f and of Ti-3d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin-orbit coupling in the same q2DES makes the LaAlO3/EuTiO3/SrTiO3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.

Using state-of-the-art, aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for an intrinsic electronic reconstruction at the LAO/STO interface is shown. Simultaneous measurements of interfacial electron density and system polarization are crucial for establishing the highly debated origin of the 2D electron gas.

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We show that the growth of the heterostructure LaGaO 3 / SrTiO 3 yields the formation of a highly conductive interface. Our samples were carefully analyzed by high resolution electron microscopy, in order to assess their crystal perfection and to evaluate the abruptness of the interface. Their carrier density and sheet resistance are compared to the case of LaAlO 3 / SrTiO 3 and a superconducting transition is found. The results open the route to widening the field of polar-nonpolar interfaces, pose some phenomenological constrains to their underlying physics and highlight the chance of tailoring their properties for future applications by adopting suitable polar materials.The quasi-two-dimensional electron gas ͑q2DEG͒ recently discovered at the LaAlO 3 ͑LAO͒ / SrTiO 3 ͑STO͒ interface 1 is presently envisaged as an ideal system for the realization of nanoscale oxide devices. 2 The electronic reconstruction model attributes the origin of the q2DEG to an electronic relaxation mechanism occurring at the interface between the ͑nominally͒ non-polar ͑001͒ STO substrate and the polar ͑001͒ LAO film. The wide band gap of LAO is considered as crucial in this approach, because it determines the capability of the polar film to transfer charges over the band gap of STO. Ideally, half an electron per areal unit cell ͑Ϸ3.3ϫ 10 14 cm −2 ͒ is expected to be transferred at the TiO 2 -LaO interface, partially filling the 3d Ti levels of the STO conduction band ͑CB͒. Alternatively, a possible active role of oxygen vacancies in STO near the interface was envisaged. 3 Actually, the transport properties of the heterostructure are affected both by oxygen pressure during growth 4,5 and by the application of an oxygen postanneal. 5 Finally, it was argued that a substantial La substitution for Sr during sample growth might drive the insulating surface of STO into a conductor. [6][7][8] Obviously, also LAO poses material issues. 9 In this context, we started the search of novel heterostructures based on a different overlayer. On this basis, we identified as a first test material LaGaO 3 ͑LGO͒, a polar, wide band gap, pseudocubic perovskite.Films of LAO and LGO were deposited on nominally TiO 2 terminated STO substrates, chemically treated in deionized water and buffered-HF. 10,11 The growth was performed by reflection high energy electron diffraction ͑RHEED͒ as-sisted pulsed laser deposition ͑KrF excimer laser, 248 nm͒ with a typical fluence of Ϸ1.5-2.5 J cm −2 at the target, a substrate temperature of 800°C and different oxygen pressures within the 10 −2 -10 −4 mbar range. 12 LAO films presented regular RHEED oscillations typical of layer-by-layer growth and a final pattern reminiscent of a single crystal surface, whereas LGO films showed damped and less regular oscillations, and a streaky 2D pattern at the end of the growth ͑Fig. 1͒.The atomic and electronic structures of LAO/STO and LGO/STO interfaces were investigated by high-resolution scanning transmission electron microscopy ͑STEM͒ and electron energy loss spectroscopy ͑EELS͒ measur...