Molecular beam epitaxy technique has enabled synthesis of atomically smooth thin films, multilayers, and superlattices of cuprates and other complex oxides. Such heterostructures show high temperature superconductivity and enable novel experiments that probe the basic physics of this phenomenon. For example, it was established that high temperature superconductivity and anti-ferromagnetic phases separate on Ångström scale, while the pseudo-gap state apparently mixes with high temperature superconductivity over an anomalously large length scale (the "Giant Proximity Effect"). We review some recent experiments on such films and superlattices, including X-ray diffraction, atomic force microscopy, angle-resolved time of flight ion scattering and recoil spectroscopy, transport measurements, highresolution transmission electron microscopy, resonant X-ray scattering, low-energy muon spin resonance, and ultrafast photo-induced reflection high energy electron diffraction. The results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations, a discovery of interface high temperature superconductivity that occurs in a single CuO 2 plane, evidence for local pairs, and establishing tight limits on the temperature range of superconducting fluctuations.Keywords: superconductivity, cuprates, interface, superlattice, field effect
ATOMIC LAYER BY LAYER MOLECULAR BEAM EPITAXYTransition metal oxides have received a great deal of recent interest due to the wealth of electronic phases that can be observed in these materials, such as multiferroicity, high-temperature superconductivity (HTS), and high mobility electron gases 1 . The underlying cause of this variety of behaviors is the strongly correlated electrons that reside in the d-orbitals of these systems. At interfaces between two such oxides the competition between different states can lead to an even wider range of phenomena than is observed in the constituent materials alone 2 . A technical hurdle to studying these interesting oxide compounds and interfaces is that the synthesis of these chemically complex materials is typically not easily achieved. We overcome this problem by employing custom-built molecular beam epitaxy systems that allow for atomic-layer-by-layer synthesis with a high degree of control over film growth [3][4][5][6] . Molecular beam epitaxy (MBE) is an ultra-high vacuum technique for deposition of thin films, typically from resistively heated thermal evaporation sources (Knudsen cells) although electron-beam sources can be used as well for refractory materials. MBE sources can be shuttered and if the system is equipped with some monitoring tools that allow for an accurate control of absolute deposition rates of respective metals, one may achieve atomic-layer-by-layer (ALL) growth. The deposition process must be controlled very accurately, at the level of one percent of an atomic monolayer or better. The BNL molecular beam epitaxy system shown in Fig. 1 is equipped with sixteen sources, ...