Yan Shao-Lin

Coupling of a Tl2Ba2CaCu2O8 Thin Film Intrinsic Josephson Junction and a Fabry—Perot Resonator

We study the electromagnetic coupling mechanism of a Tl2Ba2CaCu2O8 (Tl-2212) thin film intrinsic Josephson junction to a hemispherical Fabry—Perot resonator. An effective model to analyze coupling mechanism is put forward. The dielectric substrate is used as a dielectric resonator antenna and the Josephson junction, and a superconducting film is used as the feed line to excite a resonance mode inside the dielectric resonator antenna. To confirm this method, two Josephson junction samples with different dimensions of substrate and shapes of superconducting film are fabricated and tested under microwave irradiations. At the same time, numerical simulations of the antenna characteristics and the field distribution of these samples are performed by numerical simulation. The different coupling intensities of the two samples with the Fabry—Perot resonator fit well with the numerical simulation results. The proposed model is important for Josephson junctions used in the microwave field.

Phase Locking and Chaos in a Josephson Junction Array Shunted by a Common Resistance

The dynamics of a Josephson junction array shunted by a common resistance are investigated by using numerical methods. Coexistence of phase locking and chaos is observed in the system when the resistively and capacitively shunted junction model is adopted. The corresponding parameter ranges for phase locking and chaos are presented. When there are three resistively shunted junctions in the array, chaos is found for the first time and the parameter range for chaos is also presented. According to the theory of Chernikov and Schmidt, when there are four or more junctions in the array, the system exhibits chaotic behavior. Our results indicate that the theory of Chernikov and Schmidt is not exactly appropriate.

D.c.-SQUID of Tl-based superconducting thin film

Abstract D.c.-SQUIDs from TlBaCaCuO superconducting thin film have been fabricated. The flux modulated V−I curves and V−H curves were measured and the triangular patterns in response to flux-applied were about 20–40 μV peak to peak and for one among the d.c.-SQUIDs the amplitude of flux-voltage reached 50 μV p-p.

Miniaturized high-temperature superconducting multiplexer with cascaded quadruplet structure

In this paper, compact high temperature superconducting (HTS) multiplexers are presented for satellite communication applications. The first multiplexer consists of an input coupling node and three high-order bandpass filters, which is named triplexer. The node is realized by a loop microstrip line instead of conventional T-junction to eliminate the redundant susceptance due to combination of three filters. There are two eight-pole band-pass filters and one ten-pole band-pass filter with cascaded quadruplet structure for realizing high isolation. Moreover, the triplexer is extended to a multiplexer with six channels so as to verify the expansibility of the suggested approach. The triplexer is fabricated using double-sided YBa2Cu3O7 thin films on a 38 × 25 mm2 LaAlO3 substrate. The experimental results, when compared with those ones from the T-junction multiplexer, show that our multiplexer has lower insertion loss, smaller sizes and higher isolation between any two channels. Also, good agreement has been achieved between simulations and measurements, which illustrate the effectiveness of our methods for the design of high performance HTS multiplexers.

Energy gap suppression and excess current in Tl2Ba2CaCu2O8 intrinsic Josephson junctions

Intrinsic Josephson junctions in misaligned Tl2Ba2CaCu2O8 thin film were fabricated on LaAlO3 substrate. The temperature dependence of the critical current is investigated around liquid nitrogen temperature. In the current voltage characteristic, large voltage jump and lack of resistive branch are observed, which shows good consistency with the intrinsic Josephson junctions. By analyzing the large gap voltage in the curve, great suppression of the energy gap is found. Through discussing the temperature dependence of the gap voltage in liquid nitrogen temperature, it is shown that this phenomenon can be caused by the non-equilibrium quasiparticle injection. The temperature influence on the excess current also confirms the non-equilibrium effect.

Characteristics of Off-Chip Millimeter-Wave Radiation from Serial Josephson Junction Arrays

We investigate the self-emissions from serial high-temperature superconductor bicrystal Josephson junction arrays embedded in a quasi-optical resonator. A bicrystal substrate is used as a dielectric resonator antenna, which increases the coupling strength between the junction array and the electromagnetic (EM) wave. Both three-dimension (3D) electromagnetic simulations and experiments are performed. Strong off-chip radiations are measured from the junction array at 78 GHz and 78 K. The proposed method and the experimental results are important for millimeter wave applications in junction arrays.

A TlBaCaCuO Thin Film Planar dc-Squid Magnetometer

A superconducting quantum interference device (squid) was made from TlBaCaCuO(TBCCO) thin film. The squid loop forms a part of the pickup loop. The squid hole is a square of about 100×100 μm. The pickup loop and the squid loop inductances are estimated to be 11 nH and 190 pH, respectively. The best value of equivalent flux noise as measured in the flux locked loop mode is 4 × 10-4 0/Hz1/2 at dc-1 Hz. The corresponding sensitivity resolution at this frequency is 9 pT/Hz1/2, about a factor 8 higher than the squid loop area.

X-ray Photoelectron Spectroscopy on Superconducting Tl2CaBa2Cu2O8 Thin Film

We have prepared single-phase superconducting Tl2CaBa2Cu2O8 thin film by dc magnetron sputtering process and measured x-ray photoelectron spectra of the film at room and liquid nitrogen temperatures. From the relative intensities of the Ba3d, Tl4f. O1s and Cu2p spectra taken at different take-off angles, we have concluded that there is an adventitious contamination (nonsuperconducting phase) surface layer. After excluding contributions from these spurious phases, we have tentatively assigned which core-level shifts should be caused by the superconducting phase transition.

Fabrication and Properties of Double-Side Tl2Ba2CaCu2O8 Thin Film on CeO2 Buffered Sapphire Substrate

The double-side Tl2 Ba2 CaCu2O8 (Tl-2212) superconducting thin films were fabricated on CeO2 buffered sapphire substrates. The reactive magnetron sputtering technique was used to grow CeO2 buffer thin films on sapphire substrates. Making use of the metal cerium as a sputtering source, the depositing rate is much higher compared with the CeO2 target. The Tl-2212 thin films on CeO2 buffered sapphire substrates were fabricated by a dc magnetron sputtering and post-annealing process. The x-ray diffraction indicates that the thin film is pure Tl-2212 phase with the c-axis perpendicular to the substrate surfaces, and epitaxially grown on the CeO2 buffered sapphire. The critical transition temperature Tc is around 106K, the critical current density Jc is around 3.5MA/cm2 at 77K, and the microwave surface resistance Rs at 77K and 10 GHz of the film is as low as 390 μΩ.

Inductance of Long Intrinsic Josephson Junction Arrays Composed of Misaligned Tl2Ba2CaCu2O8 Thin Films

We observe and measure the inductance of long intrinsic Josephson junction arrays composed of misaligned Tl2Ba2CaCu2O8 thin films grown on LaAlO3 substrates. The array consists of about 9.1×103 intrinsic Josephson junctions, where 90° phase shift between ac voltage across the array and ac current flowing through has been measured. Furthermore, the voltage is proportional to the frequency of the current. The measured inductance values of the intrinsic Josephson junction arrays are basically consistent with the theoretically calculated results, confirming that the inductance is mainly due to the Josephson effect. The dependence of the array inductance on its critical current is also discussed.