POSTER SESSION 4PO9: Superconducting Electronics and Hybrid Systems

Thursday, Feb. 24, 1:45 p.m. – 3:45 p.m., Hall D (GRB)

4PO9-1 Numerical Modeling of Macroscopic Superconductivity for Microelectronics

Walter B. Richardson 1, Graham F. Carey 2, Alexandre Ardelea 2, and Anand Pardhanani 2. 1 Mathematics Dept., Univ. of Texas at San Antonio, San Antonio, TX, 78249. 2 TICAM and ASE-EM Depts., Univ. of Texas at Austin, Austin, TX, 78712.

Presenting Author: W.B. Richardson

We consider a class of macroscopic mathematical models together with their approximate analysis and numerical simulation for superconductivity applications, such as Josephson junctions. Our work complements current experimental and theoretical studies, so that existing and proposed physical models can be studied and modified accordingly. The research is a first step towards an analytic capability that will be necessary in designing superconducting microelectronics, in much the same way as process and device simulation forms an essential component of present day microelectronics design.

A hierarchy of PDE models is considered beginning with the London equations, progressing to a nonlinear scalar system, and finishing with the full Ginzburg-Landau formulation. Next we consider the numerical modeling problem for simulations in multiple dimensions. The strong nonlinearities in these equations and steep solution gradients necessitate advanced numerical methods including the use of nonuniform grids, adaptive grid refinement strategies, and preconditioning for the linearized systems.

The work will focus upon formulation and analysis of the mathematical models, development of approximate discrete schemes together with error analysis, and designing effective numerical techniques for solving the approximate problem. Numerical results for a representative physical model in the hierarchy are given.

4PO9-2 Paramagnetic Response of NS Proximity Cylinders

Kazumi Maki and Stephan Haas, Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-0484

Presenting Author: S. Haas

Since the discovery of the unusual paramagnetic reentrance behavior at ultra-low temperatures in Nb-Ag, Nb-Au, and Nb-Cu cylinders by Mota et al. in 1990, this phenomenon still remains a puzzle. For the diamagnetic response down to temperatures of the order 15 mK, the standard theory (quasi-classical approximation) for superconductors appears to work very well, assuming that Ag, Au, and Cu remain in the normal state except for the proximity-induced superconductivity. Here we propose that these noble metals may become p-wave superconductors with a transition temperature of order 10 mK. Hence, below T_c p-wave triplet superconductivity emerges around the peripherie of the cylinder. The current flowing in the peripherie is therefore reduced/compensated by a quantized paramagnetic current in the opposite direction, thus providing a simple explanation for the observed increase in the susceptibility at ultra-low temperatures.

4PO9-4 Probabilistic homogenized thermomaterial properties of periodic superconducting coil cables

Marcin Kaminski*, George Brown School of Engineering, Rice University, 6100 Main Street, Houston, TX 77005-1892, USA. *Permanent Address: Dept. of Mechanics of Materials, Technical University of Lodz, Al. Politechniki 6, 93-590 Lodz, Poland.

Presenting Author: M. Kaminski

Superconducting devices are applied in engineering practice as multicomponent materials. Some of them have perfectly periodic or quasi-periodic structure and are built up with superconducting strands twisted around the structural tube covered with jacket and insulation. Mechanical and physical properties of these components, i.e. Young moduli, Poisson's ratio as well as the coefficients of thermal expansions are determined experimentally and given in the statistical form; macro as well as microgeometry of superconducting composite structure are given deterministically.

The main problem of the study is to determine the behavior of the whole structure in terms of real external loadings and it is done by the use of simplified analytical studies or, alternatively, using Finite Element Method approach. Considering multiscale character of the problem and probabilistic character of some of design parameters so-called homogenization method is recommended that enable to consider the equivalent structure with the same external shope and boundary conditions with modified homogeneous thermomechanical and general physical properties being constant within the superconducting device.

The homogenization method applied is linked with the Monte-Carlo computational simulation technique what enable to calculate probabilistic moments of the effective material tensor components and to formulate stochastic reliability conditions for the superconducting structure analyzed.

4PO9-5 Magnetic and Superconducting Properties of CMR/HTS Multilayers for Spin Injection Devices

P. Mikheenko 1, R. Chakalov 1, F. Wellhofer 1, M. Colclough 1, C. Muirhead 1, and K. Kawano 2. 1 School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom. 2 School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.

Presenting Author: P.M. Mikheenko

We have prepared several types of double and trilayer structures from Colossal Magnetoresistance Material (CMR) and High Temperature Superconductor (HTS). These include trilayers La_0.67Sr_0.33MnO₃-SrTiO₃-YBa₂Cu₃O_x and La_0.67Ca_0.33MnO₃-SrTiO₃- YBa₂Cu₃O_x and bilayers La_0.67Sr_0.33MnO₃- YBa₂Cu₃O_x. The multilayers were prepared by laser ablation both in-situ and ex-situ on SrTiO₃ substrates with the first layer on the substrate being either the CMR or HTS material. The high quality epitaxial growth and orientation of all layers was confirmed by XRD. Mass-spectrometer analysis during Argon-ion milling shows clean and sharp boundaries between layers. Magneto-optical images demonstrate the homogeneity of the superconducting layer. The magnetic properties of multilayers were measured in a VSM in magnetic field up to 12 T and in a sensitive SQUID magnetometer up to 0.1T.

We find that the superconducting film strongly influences the magnetic state of the CMR film in that the HTS layer induces a large inhomogeneous magnetic moment in the CMR layer, resulting from the enhancement of magnetic field near the edges of superconducting sample. In turn, the CMR layer strongly influences the HTS layer, facilitating penetration of the magnetic flux at the temperatures close to T_c. We will discuss the physics of this behavior and its consequences for the operation of spin injection devices.

4PO9-6 Investigation of growth peculiarities of CMR/dielectric/HTS multilayers

R.A. Chakalov, P. Mikheenko, C.Severac, M. Alsworth, C.N.W. Darlington, F. Wellhofer, and C.M. Muirhead, School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom

Presenting Author: C. Severac

The prospect of spin-injection devices depends strongly on the development of reliable technology for the deposition of high-quality multilayer structures of colossal magnetoresistive (CMR), dielectric and high-temperature superconducting (HTS) thin films. The similar type and the close parameters of the crystal lattice of (LaSr)MnO (as CMR), SrTiO (as dielectric) and YBaCuO (as HTS) is a good precondition for successful epitaxial growth. But the electric and magnetic properties of the films are significantly influenced by such growth peculiarities as interface smoothness, atomic interdiffusion and oxygen deficiency.

Trilayer structures of (LaSr)MnO, SrTiO and YBaCuO films were deposited by laser ablation under different conditions and investigated by AFM, XRD, SIMS and magnetic susceptibility measurements. It was demonstrated by AFM that single (LaSr)MnO films are smoother than YBaCuO and for this reason these are preferable as first layer on the substrate. But the crystal lattice perfection of HTS film, when on the top, is slightly reduced, as detected by XRD. The atomic interdiffusion in both cases is negligible according to SIMS depth profiles. The "in-situ" depostiton of all three layers resulted in oxygen-deficient YBaCuO films. We found that "ex-situ" annealing in oxygen increases the critical temperature and does not deteriorate the CMR film magnetic properties.

4PO9-7 Pyroelectric/Superconducting Oxide Heterostructures for Uncooled Wide-Band Infrared Detection

N.J. Wu, Y.Q. Xu, Y.S. Chen, and A. Ignatiev, Space Vacuum Epitaxy Center and Texas Center for Superconductivity, University of Houston, Houston, TX 77204-5507

Presenting Author: N.J. Wu

Uncooled infrared detectors are currently being explored for both military and commercial uses ranging from night vision and surveillance, to fabrication processing control. The infrared detectors consisting of thin film pyroelectric/superconducting oxide-heterostructures have been fabricated. Pb(Zr,Ti)O₃ (PZT) and (La, Mn, Sb)-doped PZT thin films were integrated to YBa₂Cu₃O_7-x (YBCO) films on yttria-stabilized zirconia (YSZ)-buffered Si(100) and on LaAlO₃(100) substrates by the pulsed laser deposition technique. The YBCO thin films used as the bottom conductive electrode increase the performance of pyroelectric IR detection significantly, because YBCO has low thermal conductivity, high IR reflectance, and can be used as good templates for pyroelectric PZT film epitaxial growth. The crystalline properties and photoresponse of the oxide thin film heterostructure infrared detectors were tuned and characterized from room temperature up to the phase transition temperatures of PZT. Detectivity values of ~108 cm. Hz1/2/W at room temperature have been obtained for simple heterostructure device configurations in IR-wavelength range of 1 micro-meter to 20 micro-meter. A YBCO air-bridge has been fabricated for lower thermal mass of the heterostructures and for faster frequency-response of IR detectors.

4PO9-8 Microwave Power Absorption in HTS on the basis of Phenomenological Models

Malay Ranjan Tripathy and G.P. Srivastava, Department of Electronic Science, South Campus, University of Delhi, Delhi 110 021, India

Presenting Author: M.L. Tripathy

Microwave power absorption studies on HTS are highly relevant in order to develop the understanding of fundamental correlated physicsl processes involved in the electromagnetic interaction with materials and their applications. However, eventhough many extensive work have been carried out in the bulk, thin film and single crystals, still many of features in power absorption studies are not explained properly. In this paper we have considered few recent models and simulated for the theoretical curves, which are compared finally with the experimental results of silver doped and undoped Bi_1.84Pb_0.4Sr₂Ca_2.2Cu₃O₁₀ samples. We have simulated theoretical curves from derived relations for microwave power absorption at 10 GHz by using concept of Two Fluid Model [1], Three Fluid Model [2] and Modified Two Fluid Model of Vendik et al. [3].For all curves T_c value is considered as 110K. The other parameters are choosen more suitably considering highly granular BSCCO systems in account. In Modified Two Fluid Model the quasi particle scattering and peculiarities of the normal conductivity of the HTS at microwaves, including residual resistance of a material, are taken into account. A wide range of experimental results [3] are also varified with this model. It is seen that it has high order of accuracy between this model and observed experimental results. More over we would like to mention that our experimental results for microwave power absorption that presented here also have better agreement with the model predicted by Vendik et al. [3]. But in case of Three Fluid Model only the temperature independent normal electrons are considered which are important for residual losses and dominates at low temperatures. But it seems that there is not much difference than Two Fluid Model which can be more realistic to explain the behaviour of experimental results below T_c. Therefore we find this empirical model proposed by Vendik et al. [3] is more reliable to use for interpretaion of observed behaviour of microwave power absorption of silver doped Bi-2223 superconductors.

[1] C.J. Gorter and H.B.G. Casmir. Phys. Z., 35, 963, (1934).

[2] Y. Kobayashi and T. Imai, IEICE Trans., E74, 1986, (1991).

[3] O.G. Vendik, I.B. Vendik and D.I. Kaparker, IEEE Trans. Microwave Theory Tech., 46, 469, (1998).

4PO9-9 Periodic Thin-Film Aluminum Microstructure as a Hot-Electron Microwave Radiation Detector

Vladimir I. Kuznetsov 1, Ivan Yu. Borisenko 1, Viacheslav A. Tulin 1, and D. Esteve 2. 1 Institute of Microelectronics Technology and High-Purity Materials, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia. 2 Quantronics group, SPEC-CEA Saclay, 91191 Gif-sur-Yvette, France.

Presenting Author: V.I. Kuznetsov

We have found that the aluminum thin film structure shaped like a chain of micron-sized islands connected by narrow isthmuses, modify their electron transport and structural properties under microwave radiation at the temperature of 4.2 K. A normal metal structure transforms into a kind of lateral periodic structure N-S-N, where N is normal island and S is superconductive isthmus. The superconductive critical temperature of the isthmuses runs into 6 K, and one of island is 1.3 K.

Current-voltage characteristics of the samples under low microwave power radiation have been studied over the temperature range between 1.3 and 10 K. CVCs of modified chains are broken lines with the sections of abrupt voltage increment corresponding to the consecutive transition of the superconductive isthmuses to the normal metal state. Unexpected CVCs are due to the changes of structural properties of isthmus material and to the "diffluence" of isthmuses. The low-temperature migration of aluminum under microwave radiation has been observed in micron scale. Probably, such enigmatic phenomenon has not been observed before. The obtained structure is the row of consecutive hot electron detectors. Advantage of our detector is absence of heterojunctions. The microwave detector sensitivity makes up to 10⁵ V/W.