M. Španková

Properties of YBa2Cu3Ox and Bi2Sr2CaCu2Ox thin film microstrips patterned by argon ion beam

High temperature superconductor YBa 2 CU 3 O X (YBCO) and Bi 2 Sr 2 CaCU 2 O x (BSCCO) thin film microstrips were prepared by argon ion beam etching down to a geometrical width W g 250 nm. A study of transport properties of the superconducting microstrips showed that due to the interaction of accelerated argon ions with the superconductor film the edges of microstrips are damaged to a depth ΔW85 nm. The effective width of YBCO microstrip W ef = W g - Δ2W80 nm is able to transmit a critical current density above 20 MA/cm 2 at a temperature of 30 K and a zero external magnetic field. The critical current density of similar BSCCO microstrips was several times smaller.

Fabrication of hybrid thin film structures from HTS and CMR materials

We present the preparation of bilayers from high-temperature superconductors (HTS) and half-metallic ferromagnetic (FM) manganite with a colossal magnetoresistance (CMR). We used YBa2Cu3O7-x (YBCO) and Tl2Ba2CaCu2O8 (TBCCO) thin films as a HTS material and La0.67Sr0.33MnO3 (LSMO) film as a CMR material. In the case of YBCO/LSMO, we prepared FM/HTS heterostructure for studying the spin-polarized current injection effect on the electrical properties of the YBCO strip in dc or low-frequency regimes and on the microwave characteristics of the strip. For the first time, we report the preparation of a TBCCO/LSMO bilayer. In some applications, the TBCCO offers better parameters (higher working temperature, lower surface resistance, lower 1/f noise) than YBCO.

Structural and electrical properties of YBa2Cu3O7−x films prepared on (110) SrTiO3 single crystals or buffer layers

Abstract The structural and electrical properties of YBa2Cu3O7−x (YBCO) thin films grown on (110) planes of SrTiO3 (STO) by magnetron sputtering were studied. The growth of (103)YBCO films on (110)STO single layer crystal substrate is compared to the growth of (103)YBCO on STO buffer layers deposited by rf sputtering on a YSZ\(100)Si substrate. More predominant growth of the (103) oriented grains on STO buffer layers is considered a consequence of the small domain structure of the STO\YSZ buffer layer and lateral dynamics of the growth mechanism during the deposition of YBCO. (103) YBCO films have the c-axis 45° inclined to the substrate surface and their structural and electrical anisotropy is predicated by the microstructure of (110)SrTiO3 single crystals or STO buffer layers grown on YSZ\(100)Si substrates.

Transport properties of YBa2Cu3Ox /La0.67Sr0.33MnO3 nanostrips and YBa2Cu3Ox/La0.67Sr0.33MnO3/YBa2Cu3Ox nanojunctions

A metallic ferromagnet (F) in proximity with a superconductor (S) can transport supercurrent on a long distance through conversion of opposite-spin singlet Cooper pairs (CP) into equal-spin triplet CP (long range triplet component, LRTC), which are not broken by the exchange energy of F. The optimal conditions for the conversion are yet to be clarified; however, it is accepted that the key point to this process include high interface transparency and magnetic inhomogeneity at the SF interface. The aim of our paper is to study SF nanostrips (length of about 1500 nm and width down to 300 nm) and lateral SFS nanojunctions based on high critical temperature YBa2Cu3Ox (YBCO) and half-metallic La0.67Sr0.33MnO3 (LSMO) thin films. We applied a focused Ga+ ion beam (FIB) for patterning the SF nanostrips, as well as lateral SFS nanojunctions, by creating a slot in the nanostrip after removing the YBCO film in the slot along a length of about 200 nm. The temperature dependences of the samples resistance R(T) show critical temperature TCn ≈ 89 K of the SF nanostrips; however, the SFS nanojunctions at T < TCn show a residual resistance R < 100 Ω corresponding to a dirty LSMO (ρ≈ 10 mΩ cm) in the slot. The LRTC was not observed in our lateral SFS nanojunctions until now.

Mutual compatibility of AlGaN HEMT and HTS (YBCO) technology

The possibility of the integration of a high-temperature superconductor thin film with active GaN devices at a working temperature of liquid nitrogen (77 K) are examined. We prepare YBa2Cu3O7−x (YBCO) films using a pulsed-laser deposition method on a hexagonal GaN of AlGaN/GaN substrate and next create circular high electron mobility transistor (C-HEMT) structures on the same substrate. The YBCO films with a maximum critical temperature of ≈80 K were grown on an MgO buffered hexagonal GaN substrate. The YBCO films were grown at the maximum heater temperature of 760 °C. Structural properties of the YBCO films are presented. We applied a special fullerene mask and bromoethyl alcohol to avoid a YBCO film and MgO buffer layer from part of the AlGaN/GaN substrate. This was used for the preparation of the C-HEMT devices. We show that the 2DEG channel of transistors is not degraded despite applying the high-temperature deposition processes of the superconducting films.

The influence of the CeO2 buffered r-sapphire microstructure on the quality of the YBCO films determined by microwave measurements

Abstract Superconducting YBa 2 Cu 3 O 7 (YBCO) thin films were prepared by different deposition techniques (magnetron sputtering, laser ablation) on CeO 2 buffered r-sapphire substrates. A zero magnetic field microwave absorption measurement was used to characterize the transition of the YBCO films to the superconducting state. The obtained results were compared with the crystallographic properties (Δ ω values, morphology) of the substrates, CeO 2 buffer layers and finally with the YBCO films. Especially, we discuss about the influence of the deposition and annealing of the CeO 2 layers on the electrical properties of the YBCO films. Using rocking curve measurements, AFM and TEM analyses there were revealed structural differences in the CeO 2 layer which affect the superconducting behaviour of the YBCO films. We optimized the technological processes of the CeO 2 preparation to enhance the quality of YBCO films.