[1] CALTECH, Dept Phys, Pasadena, CA 91125 USA
[2] CALTECH, Jet Prop Lab, Ctr Space Microelect Technol, Pasadena, CA 91109 USA
[3] Pohang Univ Sci & Technol, Natl Creat Res Initiat Ctr Superconduct, Pohang 790784, South Korea
[4] Pohang Univ Sci & Technol, Dept Phys, Pohang 790784, South Korea