4PO9-70 Anisotropy of FIB-fabricated Planar SNS Junctions on (110) YBCO Thin Films

Chong Wang, Hye-Won Seo, Lixi Yuan, H.Y. Zhai, Quark Chen, and Wei-Kan Chu, Ion Beam Laboratory, Texas Center for Superconductivity, University of Houston, Houston TX

Presenting Author: C. Wang

Planar superconductor-normal metal-superconductor (SNS) tunneling junctions have been fabricated by a Focused Ion Beam (FIB) on high quality <110>-oriented YBCO thin film superconductors. The normal metal was formed by filling tungsten element into a a sub-100nm trench cut in-situ by the FIB. In this configuration, the tunneling path can be made either along the c-axis or along the ab-plane. As the coherence length is anisotropic, so is the tunneling behavior as described by the IV characteristics. This provides useful insights into the electronic structure of the constituent materials and the proximity effect at the superconductor and normal metal interface. Standard four-probe ac method based on lock-in techniques was used to investigate the dynamic conductance variation as a function of temperature and magnetic field. The significance of these findings will be discussed.

4PO9-71 Ar ion milling effect of MgO and LaAlO₃ single crystal substrates for YBa₂Cu₃O_7-d step-edge junction

Heeseok Choi 1,2, Yunseok Whang 1,2, Jin-Tae Kim 1, Soon Hee Chung 1, DongHoon Lee 2, Soon-Gul Lee 3, Yong Ki Park 1,2,3, and Jong-Chul Park 1,2,3. 1 Korea Research Institute of Standards and Science, P.O. Box 102, Yusong, Taejon 305-606, Korea. 2 Department of Physics, Paichai University, Taejon, Korea. 3 Department of Physics, Korea University, Jochiwon, Chungnam 339-800, Korea.

Presenting Author: H.S. Choi

The annealing effects of MgO and LaAlO₃ substrates ion-milled for high T_c superconducting YBa₂Cu₃O_7-d (YBCO) step-edge junction have been investigated by measuring I-V characteristic of the junction and critical current density J_c of YBCO film, and scanning surface of the substrates near step with AFM (atomic force microscope). The YBCO films are deposited on the subtrates by using pulsed laser deposition. The steps with hight of 200 nm are fabricated by Ar ion-milling (milling rate ~ 10 nm/sec).

The AFM image shows that the ion-milled surface near step is rougher than that prior to the milling and gets recovered after annealing at 1050 ° C for 1 hour at ambient pressure of oxygen. Similarly the critical current density of the YBCO on the milled surface that is lower appears to be recovered after the annealing. The I-V characteristics exhibit the above pattern; the annealing heals the damaged surface. The shape of I-V curve of the step-edge junction improved by the annealing of the substrates gets closer to RSJ model, furthermore, the yield rate of the junction formation is improved as well.

4PO9-72 Step angle effects in YBa₂Cu₃O₇ step-edge junctions prepared on sapphire substrates

Hae-Ryong Lim 1,2, In-Seon Kim 1, Dong Ho Kim 2, and Yong Ki Park 1. 1 Superconductivity Group, Korea Research Institute of Standards and Science, Yusong P.O. Box 102, Taejon 305-600, Republic of Korea. 2 Department of Physics, Yeungnam University, Kyungsan 712-749, Republic of Korea.

Presenting Author: D.-H. Kim

YBa₂Cu₃O₇ step-edge Josephson junctions have been fabricated on sapphire substrates with CeO₂ buffer layer. The steps were formed by using Ar-ion milling technique having step angles in a wide range (from 20 to 70 degree). The current-voltage curves of the junctions formed on low angle (below 50 degree) steps exhibit RSJ-like behaviors at 77 K. The critical current (I_c) decreased and normal resistance (R_n) increased with increasing the step angle) in the range from 20 to 40. Large IcRn product of 0.25 mV with junction resistance R_n= 5 W and critical current I_c= 0.05 mA at 77 K could be obtained reproducibly with 5 micron microbridges formed on 35 degree steps. The temperature dependence of the critical current and the normal resistance suggests a metallic barrier as interface layer in a SNS-type junction.

4PO9-73 dc magnetic field-induced decrease of microwave surface impedance in superconducting thin films

X.S. Rao, C.K. Ong, B.B. Jin, and Y.P. Feng, Centre for Superconducting and Magnetic Materials and Department of Physics, National University of Singapore, Singapore 119260

Presenting Author: C.K. Ong

An anomalous response in Z_S of high temperature superconducting (HTS) YBa₂Cu₃O_7-d thin films, i.e., R_S and X_S show a minimum in the presence of weak dc magnetic field, was observed at K using a microstrip resonator technique. The anomaly was investigated at different dc field orientations, microwave input power levels, frequencies, and in samples with different film qualities as well. We found experimentally that the anomalous effect is mainly contributed by the granular nature of the HTS films under test though the exact origin is still not known yet. We have shown that both Josephson and Abrikosov vortex penetration tend to suppress the anomalous effect. It has also been shown that the anomalous decrease of Z_S happens at a dc field scale far below the lower critical field of the superconducting films.

4PO9-74 Polariton-like Interaction between Microwaves and Electronic Subsystem of Metal Oxide Superconductor

V.A. Dravin, Yu.F. Eltsev, A.L. Karuzskii, V.N. Murzin, A.V. Perestoronin, and P.P. Sverbil, P.N.Lebedev Physical Institute of RAS, Leninsky pr. 53, 117924 Moscow, Russia

Presenting Author: A.L. Karuzskii

In studying the microwave (10 GHz) response of both single crystal and ceramic samples of the YBaCuO(123) in Nb resonator we have found strongly wavevector-dependent dielectric permittivity resulting in appearance of the new dielectric resonances with hysteretic temperature behaviour. The data show the importance of the nonconducting "bound" electron polarization in strong local fields and spatial dispersion which lead to the polariton-like interaction between microwaves and electrons in HTSC. The effects of the polariton-like microwave excitations on the limiting mechanisms in superconducting cavities are discussed.

4PO9-75 Experimental investigation of local nonlinear microwave response of HTS ceramics

Yuri Nozdrin, Vladislav Kurin, Evgeny Pestov, and Michael Rzhavin, Institute for Physics of Microstructures, Russian Academy of Sciences, 603600, Nizhny Novgorod, GSP-105, Russia

Presenting Author: M. Rzhavin

One of the most promising applications for high-T_c superconductors (HTS) is found in the field of passive microwave devices, where a highly linear microwave response is required. Nonlinear properties limit this application, but microscopic origin of nonlinearly at microwave frequencies in HTS has not yet been generally identified. For the research of microwave nonlinearity we used the local measurements of the third harmonic power at f₀=470MHz. Using a probe with inductive coupling the map of nonlinear microwave response for ceramic YBaCuO sample was plotted both without dc magnetic field and for different values of this one. The third-harmonic power was measured as a function of temperature (from T=20K to T_c=90K), input power, and dc magnetic field at some places of the sample surface. The measured temperature dependence of third-harmonic power strongly varies from that one obtained for thin films. The P₃ (P₀) dependence follows a cubic law only at small input powers P₀ and at low temperature. The measurements show for nonlinear response to be suppressed by the dc magnetic field. The presented technique and experimental results are used for research of nonlinear mechanisms in HTS.

4PO9-77 The persistent current qubit: Coherence and Measurement

Frank K. Wilhelm, C.H. van der Wal, C.J.P.M. Harmans, and J.E. Mooij, Quantum Transport Group, Department of Applied Physics, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands

Presenting Author: Frank K. Wilhelm

We investigate this scenario by applying a generalized master-equation formulation of the driven spin-boson model. We derive the characteristic time scales. Criteria for the design parameters are discussed together with the present experimental status.

4PO9-78 Hg-based HTS loop antenna used for the demonstration of a passive radiative cooler for spacecraft

Cao Bisong 1, Yuyi Xue 1, Jaroslaw Wosik 1, Leiming Xie 1, Shenghui Xu 1, Ruling Meng 1, Meihong Zhu 2, and C.W. Chu 1. 1 TCSUH, University of Houston, Houston, TX 77204-5932, USA. 2 Department of Physics, Tsinghua University, Beijing 100084, China.

Presenting Author: M.H. Zhu