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Controlled trapping and guided motion of vortices via special arrangements of microholes, so-called antidots, in YBa 2 Cu 3 O 7 films and devices is demonstrated. Resistive Hall-type measurements prove the presence of guided flux motion along rows of antidots. In contrast to conventional vortex motion due to vortex unpinning at currents exceeding the critical current, this motion is present down to zero current and low temperatures. It is characterized by a linear voltage-current dependence, i.e., Ohmic behavior. The latter is indicative for a novel mechanism of vortex propagation that is probably based upon flux nucleation within antidots due to the redistribution of screening currents and flux quantization. Together with trapping of vortices by isolated antidots this mechanism can be used for new devices concepts. As an example a vortex ratchet formed by a special arrangement of antidots is demonstrated.

Optimized sputtered YBa2Cu3O7 (YBCO) thin films on CeO2-buffered sapphire substrates are patterned into square lattices of submicrometer holes (antidots) with diameters of 250–450 nm and lattice parameters of d=500–1000 nm without deterioration of superconducting properties. In the mixed state, matching effects between the Abrikosov vortex lattice and the artificial antidot lattice are observed. These effects are in the form of peaks or cusps in the critical current density recorded as a function of magnetic induction at integers n and specific rationals k/l of the matching field Bm=(Φ0/d2). The experimental results are discussed in the context of existing theories. The existence of multiquanta vortices confined by the holes in YBCO films are considered.

An overview of the deposition and deposition techniques (with the emphasis on PVD techniques) of high-T c material is presented. The major technologies are discussed and compared, and advantages and problems of various substrate materials are illustrated. The consequences connected with lattice mismatch are discussed, and film nucleation and growth modes of ceramic superconducting material are sketched. Finally, remaining areas for further research are listed.

The microwave properties of single crystalline TiO2 (rutile) were investigated. At a frequency of 7.5 GHz the loss tangent tan δ was found to increase from 1.4×10−7 at 4 K to 4×10−6 at 70 K for electric fields parallel to the crystallographic a,b plane. The high permittivity of 105 and the small tanδ in combination with the low microwave losses of high temperature superconductors (HTS) were utilized to construct a miniaturized X-band resonator with a high quality factor Q. An assembly of two YBa2Cu3O7 films of 8 mm in diameter separated by a rutile cylinder of 2 mm height provides a TE011 resonance at 9.7 GHz with Qs ranging from 6×105 at 10 K to 105 at 70 K. Frequency scaling of the losses in rutile and in the HTS films indicates Qs in excess of 106 at 1.8 GHz using YBa2Cu3O7 films of two inches in diameter. Such resonators are considered to be key elements for high-power filters in mobile communications.

Vortex ratchet effect is investigated experimentally in the frequency range between 0.5 MHz and 2 GHz. The ratchet potential is provided by an array of about a quarter of a million nanoengineered asymmetric antidots in a Pb film. A square vortex lattice is stabilized at the first matching field, when each asymmetric antidot is occupied by a single vortex. We have found that ͑1͒ the transition from adiabatic to nonadiabatic cases occurring at about 1 MHz, above which the ratchet windows shift upwards with the applied frequency due to the fact that the time for a vortex to escape from the pinning potential is comparable to the period of the applied rf driving current I rf ; ͑2͒ a sudden V dc reversal at large I rf , which can be attributed to inertia effect; ͑3͒ the collective step-motor behavior in the MHz region, i.e., the vortex lattice moves forward by an integer number of the period of pinning array at each cycle of I rf ; and ͑4͒ very weak ratchet effect at several GHz, indicating the possibility of stronger inertia effects in the vortex motion at such high frequencies. These results reveal rich physics information in the nonadiabatic ratchet system and are of particular importance for particle separation and molecular motor in biology.

The impact of strain on structure and ferroelectric properties of epitaxial SrTiO 3 films on various substrate materials-substrates with larger ͑DyScO 3 ͒ and smaller ͑NdGaO 3 and CeO 2 /Al 2 O 3 ͒ in-plane lattice constant, respectively-was analyzed. In all cases, ͑001͒-oriented strained epitaxial SrTiO 3 was obtained. It is demonstrated that the mismatch of the lattices or, alternatively, the mismatch of the thermal expansion coefficients of films and substrate, imposes biaxial strain on the SrTiO 3 films. The strain leads to a small tetragonal distortion of the SrTiO 3 lattice and has a large impact on the ferroelectric properties of the films. With decreasing film thickness and at low temperatures the permittivity deviates from the "classical" Curie-Weiss behavior. Furthermore, strain-induced ferroelectricity is observed, which agrees with theoretical predictions. For electric fields parallel to the film, surface-induced ferroelectricity is observed for SrTiO 3 that is exposed to in-plane tensile strain, i.e., SrTiO 3 on DyScO 3 and sapphire. Transition temperatures of T o Ϸ 210 K and T o Ϸ 325 K are obtained for SrTiO 3 on CeO 2 /Al 2 O 3 and DyScO 3 , respectively.

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