Peak effect in a superconducting DyBa2Cu3O7-δ film at microwave frequencies Bhangale, A.R.; Raychaudhuri, P.; Sarkar, S.; Banerjee, Tamalika; Bhagwat, S.S.; Shirodkar, V.S. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We report the observation of a peak in the microwave ͑9.55 GHz͒ surface resistance in an epitaxial DyBa 2 Cu 3 O 7Ϫ␦ superconducting film in magnetic fields ͑parallel to the c axis͒ ranging between 0.2 to 0.9 T. Such a peak is absent in the measurements done in zero field. The temperature and field dependence of the peak suggests that this peak could be associated with the peak effect ͑PE͒ phenomenon reflecting the orderdisorder transformation in the flux-line lattice ͑FLL͒. A strong frequency dependence of the PE is observed close to the depinning frequency of the FLL.

In this paper we report the observation of a peak in the microwave surface resistance (at frequencies ~10GHz) of laser ablated DyBa 2 Cu 3 O 7-δ films in magnetic field ranging from 2 to 9kOe ( ||c ) close to the superconducting transition temperature (T c (H)).

Calcium Fluoride bu er lavers were grown on Si 100 substrates using the low energy cluster beam deposition technique. The lms were annealed at various temperatures ranging between 500 o C and 700 o C. The SEM studies showed that as-deposited lms were well oriented along the c-axis and had very smooth surface morphology. The annealed lms on the contarary, showed lowering of peak intensities and roughening of the surface. The dielectric constant derived from the C-V measurements at 1 MHz were 2.01 and 18 for as-deposited and annealed lms respectively. I IntroductionIt seems highly probable that High Tc superconducting thin lms will have an impact on microelectronics by making it possible to grow l o w dispersion, high speed dense superconducting interconnects 1 . Another major area where the low-loss properties of the superconductors will potentially have an impact is the devices operating at microwave frequencies 2 . One major obstacle to the above applications is the di culty to grow high Tc superconducting lms on silicon. This arises due to the fact that silicon di uses into the superconducting lm during annealing at elevated temperatures resulting in broad transitions and low critical current densities 3,4 . Hence a class of materials called alkaline earth uorides, or lIa-uorides as they are commonly known, have been investigated for its usefulness to overcome this di culty. These compounds have a low dielectric constant which decreases with decreasing temperature 5 . Moreover, they are chemically stable and structurally compatible with a number of semiconductors viz., Si, GaAs etc 6 . They also have good thermal match o wing to their ionic nature 7 . The surface elds in an ionic compound decreases exponentially leading to an interface wherein the bonds across the interface tend to be weak. This allows to overcome the lattice mismatch strain by rearrangement of dislocations.Various techniques such as sputtering 8 , pulsed laser deposition 9 etc., have been employed to obtain good quality bu er layers on silicon. The low energy cluster beam deposition technique, a variant of ionized cluster beam deposition technique, involves formation of clusters of the materials to be deposited which i s charged in a specially designed crucible. The material vapours escaping the nozzle of the crucible undergo sudden adiabatic expansion and some of it form clusters. These clusters subsequently move t o wards the substrate at an ejection velocity and deposit on it. One of the greatest advantages of the low energy cluster beam deposition technique is the absence of electrical charge e ect which can in uence the nucleation and growth process.

We report on direct evidence of the suppression of critical current due to pair-breaking in a superconducting microbridge when the measurement is carried out by injecting spin-polarized carriers instead of normal electrons. A thin layer of La0.7Ca0.3MnO3 was used as the source of spin-polarized carriers. The microbridge was formed on the DyBa2Cu3O7−δ thin film by photolithographic techniques. The design of our spin-injection device allowed us to inject spin-polarized carriers from the La0.7Ca0.3MnO3 layer directly to the DyBa2Cu3O7−δ microbridge (without any insulating buffer layer) making it possible to measure the critical current when polarized electrons alone are injected into the superconductor. Our results confirm the role of polarized carriers in breaking the Cooper pairs in the superconductor.

No abstract