SrRuO 3 is endowed with three remarkable features. First, it is a moderately correlated material that exhibits several novel physical properties; second, it permits the epitaxial growth of essentially single-crystal films; and third, because it is a good conductor, it has attracted interest as a conducting layer in epitaxial heterostructures with a variety of functional oxides. In this review, the present state of knowledge of SrRuO 3 thin films is summarized. Their role as a model system for studying magnetism and electron transport characterized by intermediate electron correlation and large magnetocrystalline anisotropy is demonstrated. The materials science of SrRuO 3 thin film growth is reviewed, and its relationship to electronic, magnetic, and other physical properties is discussed. Finally, it is argued that, despite all that has been learned, a comprehensive understanding of SrRuO 3 is still lacking and challenges remain.American Physical Society

As discovered by Ohtomo and Hwang, a large sheet charge density with high mobility exists at the interface between SrTiO 3 and LaAlO 3 . Based on transport, spectroscopic, and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also present a model that explains the high mobility based on carrier redistribution due to an increased dielectric constant.

The polar Kerr effect in the high-T c superconductor YBa 2 Cu 3 O 6x was measured at zero magnetic field with high precision using a cyogenic Sagnac fiber interferometer. We observed nonzero Kerr rotations of order 1 rad appearing near the pseudogap temperature T and marking what appears to be a true phase transition. Anomalous magnetic behavior in magnetic-field training of the effect suggests that time reversal symmetry is already broken above room temperature. , large compared to the superconducting (SC) transition temperature, T c . Two major classes of theories have been introduced in an attempt to describe the pseudogap state: One in which the pseudogap temperature T represents a crossover into a state with preformed pairs with a d wave gap symmetry [6,7], and another in which T marks a true transition into a phase with broken symmetry that ends at a quantum critical point, typically inside the superconducting dome. While at low doping this phase may compete with superconductvity, it might provide fluctuations that are responsible for the enhanced transition temperature near its quantum critical point (e.g., as in Ref. [8] In this Letter, we report high resolution optical Kerreffect measurements on YBa 2 Cu 3 O 6x crystals with various hole concentrations p. (p is, in turn, a monotonic function of the oxygen concentration x, and it also depends on oxygen ordering in the chains [12].) We identify a sharp phase transition at a temperature T s p, below which there is a nonzero Kerr angle, indicating the existence of a phase with broken time reversal symmetry (TRS). Both the magnitude and hole concentration dependence of T s are in close correspondence with those of the pseudogap crossover temperature, T , which has been identified in other physical quantities. In particular, as shown in Fig. 1, T s is substantially larger than the superconducting T c in underdoped materials, but drops rapidly with increasing hole concentration, so that it is smaller than T c in a near optimally doped crystal and extrapolates to zero at a putative quantum critical point under the superconducting dome. The magnitude of the Kerr rotation in YBa 2 Cu 3 O 6x (YBCO) is smaller by 4 orders of magnitude than that observed in other itinerant ferromagnetic oxides [13,14], and the temperature dependence is ''superlinear'' near T c , FIG. 1 (color online). The onset of the Kerr-effect signal, T s (circles), and T c (red squares) for the YBa 2 Cu 3 O 6x samples reported in this Letter. Also shown are T c p (from [12]) and T N p (from [22]).

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

Ultrathin films of the itinerant ferromagnet SrRuO 3 were studied using the transport and magneto-optic polar Kerr effect. We find that below 4 monolayers, the films become insulating and their magnetic character changes as they loose their simple ferromagnetic behavior. We observe a strong reduction in the magnetic moment which for 3 monolayers and below lies in the plane of the film. Exchange-bias behavior is observed below the critical thickness and may point to induced antiferromagnetism in contact with ferromagnetic regions.

Ionic crystals terminated at oppositely charged polar surfaces are inherently unstable and expected to undergo surface reconstructions to maintain electrostatic stability. Essentially, an electric field that arises between oppositely charged atomic planes gives rise to a built-in potential that diverges with thickness. Here we present evidence of such a built-in potential across polar LaAlO3 thin films grown on SrTiO3 substrates, a system well known for the electron gas that forms at the interface. By performing tunneling measurements between the electron gas and metallic electrodes on LaAlO3 we measure a built-in electric field across LaAlO3 of 80.1 meV/Å. Additionally, capacitance measurements reveal the presence of an induced dipole moment across the heterostructure. We forsee use of the ionic built-in potential as an additional tuning parameter in both existing and novel device architectures, especially as atomic control of oxide interfaces gains widespread momentum.As dictated by Maxwell's equations, the accumulation of screening charges at the boundary between dissimilar materials is one means 1 of ensuring a continuous electric displacement at the interface. 2 For instance, a layer of trapped screening charge forms the two dimensional electron gas that compensates a polarization mismatch at gallium nitride 3 and zinc oxide 4 based heterostructure interfaces. In insulating oxides, charge accumulation was observed at the interface between SrTiO 3 substrates with atomically precise surfaces and polar LaAlO 3 films. 5 LaAlO 3 thin films grown on singly terminated SrTiO 3 surfaces 6 comprise negatively charged AlO 2 and positively charged LaO end planes and are polar in the ionic limit. 1,7,8 When at least four unit cells (u.c.) of LaAlO 3 are deposited on TiO 2 terminated SrTiO 3 , an electron gas forms near the interface in SrTiO 3 . 5,9,10 It is often hypothesized that at a thickness of four u.c. the potential across LaAlO 3 exceeds the band gap of SrTiO 3 and electrons tunnel from the valence band of LaAlO 3 to the SrTiO 3 potential well, completely diminishing the potential across LaAlO 3 . 11 Thus within this picture, in the presence of an electron gas no field would be expected across the LaAlO 3 . However, if all the charge carriers do not lie precisely at the interface or have an extrinsic (oxygen vacancies 12 or cation doping 13 ) origin, the LaAlO 3 potential will not be fully screened and can thus be probed. 14 Alternatively, the precise band alignment between the LaAlO 3 and SrTiO 3 will also determine the strength of the residual fields in the LaAlO 3 . 15 Addressing this issue by determining the existence of an uncompensated built-in potential in LaAlO 3 is central to understanding the true nature of the polar LaAlO 3 /SrTiO 3 interface.We probe the potential landscape across the LaAlO 3 and the interface region in SrTiO 3 by employing a typical metal-insulator-metal capacitor geometry such that the LaAlO 3 thin films form the dielectric layer sandwiched between evaporated metallic electrodes an...

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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.