We report on the optical properties of the hole-doped manganites Nd 0.7 Sr 0.3 MnO 3 , La 0.7 Ca 0.3 MnO 3 , and La 0.7 Sr 0.3 MnO 3 . The low-energy optical conductivity in the paramagnetic-insulating state of these materials is characterized by a broad maximum near 1 eV. This feature shifts to lower energy and grows in optical oscillator strength as the temperature is lowered into the ferromagnetic state. It remains identifiable well below T c and transforms eventually into a Drude-like response. This optical behavior and the activated transport in the paramagnetic state of these materials are consistent with a Jahn-Teller small polaron. The optical spectra and oscillator strength changes compare well with models that include both double exchange and the dynamic Jahn-Teller effect in the description of the electronic structure.

Electro‐optic modulators are among the most important building blocks in optical communication networks. Lithium niobate, for example, has traditionally been widely used to fabricate high‐speed optical modulators due to its large Pockels effect. Another material, barium titanate, nominally has a 50 times stronger r‐parameter and would ordinarily be a more attractive material choice for such modulators or other applications. In practice, barium titanate thin films for optical waveguide devices are usually grown on magnesium oxide due to its low refractive index, allowing vertical mode confinement. However, the crystal quality is normally degraded. Here, a group of scandate‐based substrates with small lattice mismatch and low refractive index compared to that of barium titanate is identified, thus concurrently satisfying high crystal quality and vertical optical mode confinement. This work provides a platform for nonlinear on‐chip optoelectronics and can be promising for waveguide‐based optical devices such as Mach–Zehnder modulators, wavelength division multiplexing, and quantum optics‐on‐chip.

Magnetic interactions in solids are normally mediated by short-range exchange or weak dipole fields. Here we report a magnetic interaction that can propagate over long distances (∼10 nm) across a polar insulating oxide spacer. Evidence includes oscillations of magnetization, coercivity and field-cooled loop shift with the thickness of LaAlO3 in La0.67Sr0.33MnO3/LaAlO3/SrTiO3 heterostructures. Similar modifications of the hysteresis loop appear when two coupled films of La0.67Sr0.33MnO3 are separated by LaAlO3, or another polar insulator, but they are absent when the oxide spacer layer is nonpolar. The loop shift is attributed to strong spin–orbit coupling and Dzyaloshinskii–Moriya interaction at the interfaces. There is evidence from inelastic light scattering that the polar spacer mediates long-range transmission of orbital magnetization. This coupling mechanism is expected to apply for any conducting ferromagnetic oxide with mixed valence; in view of electron hopping frequency involved, it raises the prospect of terahertz tunability of magnetic coupling.

Fundamental issues in pre aring high quality high T YBa&u,O thin films are adgessed. The techniques of inverted q%idrical magnetron sputtering and pulsed laser deposition are chosen as successful examples to illustrate how the key problems can be solved. The fabrication of YBa2(3l,O,$PrBa;?Cu307-su erlattices where superconductivity in a singfe unit celrlayer of YB Cu30 -x was observed demonstrates the state of the art of%in fi6n deposition of high T, materials. Systematic variations of the deposition parameters result in changes of superconducting and structural properties of the films that correlate with their microwave and infrared characteristics.

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