The use of a high-temperature superconducting probe for in vivo magnetic resonance microscopy at 2 T is described. To evaluate the performance of the probe, a series of SNR comparisons are carried out. The SNR increased by a factor of 3.7 compared with an equivalent copper coil. Quantitative measures of the SNR gain are in good agreement with theoretical predictions. A number of issues that are unique to the application of HTS coils are examined, including the difficulty in obtaining homogenous excitation without degrading the SNR of the probe. The use of the HTS probe in transmit-receive mode is simple to implement but results in nonuniform excitation. The effect of using the probe in this mode of operation on the T1 and T*2 contrast is investigated. Methods for improving homogeneity are explored, such as employing a transmit volume coil. It is found that the cost of using an external transmit coil is an increased probe noise temperature and a reduced SNR by ∼30%. Other important aspects of the probe are considered, including the effect of temperature on probe stability. Three-dimensional in vivo imaging sets are acquired to assess the stability of the probe for long scans. High-resolution images of the rat brain demonstrate the utility of the probe for microscopy applications. Magn Reson Med 41:72-79, 1999. © 1999 Wiley-Liss, Inc.

We present the results from sodium magnetic resonance imaging (MRI) experiments using high-temperature superconducting (HTS) receiver coils. Sodium imaging has been shown to have great potential for the assessment of cell integrity but suffers from a substantially lower signal-to-noise ratio (SNR) than that of hydrogen imaging. The use of an HTS receiver coil was found to significantly increase the SNR relative to an equivalent copper receiver coil at room temperature. The SNR gains afforded by HTS coils can also be used to decrease the imaging time.

We have investigated the optical response of 700 nm optically thick Tl2Ba2CaCu2O8 and Tl0.5Pb0.5Sr2(Ca0.8Y0.2)Cu2O7 high Tc superconductor films activated by a few mJ/cm2 laser pulses. We have systematically studied the dependence of optical response on temperature and laser intensity. Fast and slow components can be clearly identified. A 70 ps electric transient has been obtained when activated by a 3.3 mJ/cm2 laser at 80 K or by a 10 mJ/cm2 laser at 50 K.

We report the growth of c-axis oriented, epitaxial thin films of (Tl,Pb)Sr/sub 2/CuO/sub 5/ on (100) oriented LaAlO/sub 3/ substrates by off-axis sputter deposition in the presence of thallium oxide vapor. These films display a resistivity which crosses over from metallic to semiconducting behavior at low temperature. In addition, we have shown that multiple layers of superconducting (Tl,Pb)Sr/sub 2/Ca/sub 0.8/Y/sub 0.2/Cu/sub 2/O/sub 7/ (1212) and nonsuperconducting (Tl,Pb)Sr/sub 2/CuO/sub 5/ (1201) can be deposited sequentially without compromise of the superconducting properties of the 1212 layer. Bilayers of both 1212 on 1201 and of 1201 on 1212 have been fabricated. In either case, both materials grow with their c-axis normal to the substrate surface and with their a-axes aligned to each other and to the major axes of the substrate. Technologically interesting trilayer structures of 1212/1201/1212 have also been fabricated. Both 1212 layers are superconducting with transition temperatures of up to 94 and 93 K for the upper and lower layers respectively. We believe that this is an important step towards the development of thallium cuprate-based multilayer technology.< >

A new method of generating ultra-wide-band electromagnetic pulses using a Tl2Ba2CaCu2O8 high T(c) superconductor as a fast laser activated opening switch is presented. The superconductor is used as an opening switch with a current charged transmission line pulse forming network to produce jitter-free triggered square pulses which are radiated by an ultra-wide-band conical antenna. We report radiation and reception of pulses with center frequencies near 3.5 GHz and a bandwidth in excess of 80%. We also discuss how this technique can be used to assess various wide-band antenna designs.

We report the growth of thin films of (Tl,Pb)Sr2Ca1−xYxCu2O7 with x=0–0.2 by off-axis magnetron sputtering in the presence of thallium oxide vapor. The (Tl,Pb)Sr2Ca1−xYxCu2O7 films are highly c-axis oriented on the pseudocubic (100) surface of LaAlO3 or on (001)NdGaO3. The 〈100〉 axes of the films grown on LaAlO3 align to the pseudocubic 〈100〉 axes of the substrate while for films on NdGaO3 they are rotated 45° relative to orthorhombic 〈100〉 substrate axes. After an in situ heat treatment, undoped (Tl,Pb)Sr2CaCu2O7 films are superconducting at temperatures up to 82 K, compared with 85 K for the bulk material. Yttrium doping on the calcium site increased the transition temperature as expected. The highest transition temperature observed was 86 K for x=0.1 and 93 K for x=0.2.

The first fabrication of 3-in-diameter, thin films of thallium-based superconductors is reported. (Tl/sub 0.5/Pb/sub 0.5/)Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9/ thin films on LaAlO/sub 3/ are found to display the best surface resistance (R/sub s/) properties of any superconductor at higher temperatures and show approximately 50* better performance than copper at 100 K and 10 GHz. A Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin film, processed as a 1.8-m-long, 10- mu m-wide meander line carries about 1*10/sup 7/ A/cm/sup 2/ at 4.2 K and 2*10/sup 6/ A/cm/sup 2/ at 80 K. The thallium-based superconductors are compared to YBa/sub 2/Cu/sub 3/O/sub 7/ with respect to T/sub c/, R/sub s/, and Q.< >

Epitaxial Tl/sub 0.5/Pb/sub 0.5/Sr/sub 2/CaCu/sub 2/O/sub 7/ films produced by RF magnetron sputtering followed by annealing in the presence of thallium oxide vapor have been produced on

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Y. Liu, Y. Lai, W. Cao, C. H. Lee, S. N. Mao, X. X. Xi, T. Venkatesan, Z. Shen, P. Pang, D. J. Kountz, and W. L. Holstein, "Optical Control of High Speed Circuit Using Picosecond High Temperature Superconductor Opening Switches," in Ultrafast Electronics and Optoelectronics, J. Shah and U. Mishra, eds., Vol. 14 of OSA Proceedings Series (Optica Publishing Group, 1993), paper J1. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Several high-temperature-superconductor-sapphire TE/sub 011/ mode resonators were designed, fabricated, and tested. At 5.552 GHz, Q/sub 0/ reached 2*10/sup 6/ at 90 K, 3*10/sup 6/ at 80 K, and 1.4*10/sup 7/ at 4.2 K with circulating power up to 500 kW. Formulas for calculating the resonant frequency and Q-value were derived. These theoretical results showed good agreement with the experimental measurements. Applications such as frequency-stabilized oscillators and filters, and the characterizations of high-temperature superconductor films are discussed.<>

A two-step process for the fabrication of 0.12-1.20- mu m-thick Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films on

A two-step process for the fabrication of 0.12-1.20-mu-m-thick Tl2Ba2CaCu2O8 films on (100) LaAlO3 has been developed. The process involves the deposition of a BaCaCuO precursor film at low temperature by rf magnetron sputtering, followed by annealing in the presence of Tl2O vapor to convert the precursor film into Tl2Ba2CaCu2O8. Over a distance of 4 cm, film composition was Tl:Ba:Ca:Cu = 2.05 +/- 0.09:2.05 +/- 0.06:1.01 +/- 0.03: 1.94 +/- 0.06 and thickness was uniform to within 6%. The films contain only trace quantities of secondary phases and are epitaxially oriented, with the c-axis of Tl2Ba2CaCu2O8 perpendicular to the surface and the two a-axes aligned with the pseudo-cubic a-axes of the underlying LaAlO3 substrate. Films had a T(C) for zero dc resistivity of 106.5 +/- 0.5 K, a transport critical current density for continuous current of 2.9 x 10(6) A-cm-2 at 4.2 K and 2.7 x 10(5) A-cm-2 at 77 K, and a sharp (< 0.3-degrees-C) ac inductance transition with an onset temperature of 105 +/- 2 K. Surface resistance at 20 GHz less than 2 m-OMEGA, about 10X lower than Cu, was routinely achieved for temperatures below 90 K and, for the best films, at temperatures up to 100 K. Surface resistance at about 10 GHz on one film was 0.067 m-OMEGA at 4.2 K, 0.36 m-OMEGA at 77 K, and 0.74 m-OMEGA at 90 K. Films have been reproducibly fabricated on substrates up to 2.54 cm square.