Fabrication of Nb-based Superconducting Single Electron Transistor
Nam Kim, Klavs Hansen, Jukka Pekola, Sorin Paraoanu
Department of Physics, University of Jyväskylä, P.O.Box 35, FIN-40351 Jyväskylä
We have fabricated Nb/(Al-)AlOx/Nb junctions with a single electron transistor (SET) geometry using conventional e-beam lithographic technique. It was possible to reach a clearly defined superconducting gap of 0.75meV as measured in the current vs voltage (I-V) characteristic curve, which corresponds to Tc of 4.6 K. The Josephson coupling energy EJ=(h/4e2)·(DNb/2Rn) » 32 meV was comparable to the charging energy Ec » 35 meV which was determined from the I-V curves as function of gate voltages. From the period of the gate modulated current we estimate the gate capacitance Cg to be 15 aF which coincides with that of Al/AlOx/Al SET fabricated by us with the same geometry.
Mesoscopic effect observed in YBa2Cu3O7-d/La0.67Sr0.33MnO3 tunnel junctions
H. Kashiwayaa, A. Sawab, S. Kashiwayac, I. Kurosawaa, H. Tsuchiurad, Y. Tanakad
aDept. of Mathematical and Physical Sciences, Japan Women's Univ. & CREST, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo, 112-8681, Japan
bCorrelated Electron Research Center of AIST, Umezono 1-1-1, Tsukuba, Ibaraki, 305-8562, Japan
cNRI of AIST & CREST of JST, Tsukuba Central 2, Tsukuba, Ibaraki, 305-8568, Japan
dNagoya Univ. & CREST of JST, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
The transport properties of YBCO/LSMO tunnel junctions have been studied at ultra-low temperature in order to clarify the influences of strong correlation on transport. The conductance spectra vary from usual BTK type to the phase coherent transport as the junction size becomes smaller. Conductance spectra obtained from small junctions show a periodic response to the applied magnetic field, which suggests the presence of the Aharanov-Bohm effect in the LSMO electrode.
SQUID-detected NMR and MRI in Microtesla Magnetic Fields
Robert McDermotta, Andreas H. Trabesingerb, SeungKyun Leea, Michael Muecka, Erwin L. Hahna, Alexander Pinesb, John Clarkea
aDept. of Physics, UC Berkeley and LBNL
bDept. of Chemistry, UC Berkeley and LBNL
We have used a low-Tc SQUID to acquire nuclear magnetic resonance (NMR) spectra and magnetic resonance images (MRI) of room temperature samples in magnetic fields of a few microtesla, where the proton Larmor frequency is of the order of 100 Hz. The sensitivity of the SQUID magnetometer is independent of frequency. It is therefore possible to enhance both signal-to-noise ratio and resolution by detecting the NMR signal in microtesla fields, where the NMR lines become extremely narrow. We present spectra of heteronuclear coupled spin systems and MRIs of distilled water phantoms, and report on the progress of a SQUID-based system for in vivo MRI.
Mobile High-Tc dc SQUID magnetometer
D.F. Hea, M. Yoshizawab
aIwate Industrial Promotion Center, Morioka 020-0045, Japan
bFaculty of Engineering, Iwate University, Morioka 020-8551, Japan
By optimizing the designing, we made a smaller and low noise high-Tc dc SQUID readout electronics with the modulation freqency of 80 kHz. The white flux noise was about 30 mF0/Ö{Hz} when Sumitomo dc SQUID sensor was used. We also proved mobile high-Tc dc SQUID magnetometer was feasible. By using a special compensation method, the SQUID magnetometer could keep locked when it swung about 20 degree in the earth field. This system can be used to detect the defects in ferromagnetic material or to be mounted in plane or boat for other applications.
A Scanning SQUID Microscope in a Dilution Refrigerator
Per G. Björnsson, Kathryn A. Moler
Department of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305-4045
We have designed and built a scanning SQUID microscope in a dilution refrigerator, capable of magnetic imaging at temperatures down to 20 mK. As sensors we use susceptometer SQUIDs with two pickup loops and on-chip field coils to allow measurement of both the magnetic susceptibility of the sample and the magnetic field at the sample surface on a mesoscopic lenth scale. The instrument is useful for studying superconductivity and magnetic effects in novel materials and electronic coherence effects (such as persistent currents) in mesoscopic systems.
A digital SQUID controller
B. Limketkai, J. Granger, M. Weilert, Inseob Hahn
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
We describe the design, performance and limitation of an improved dc SQUID controller base upon a PC data acquisition board with a single digital signal processor (DSP). The main DSP algorithm that handles the flux-locked-loop, is optimally written in the DSP assembly language to minimize total execution time. The system is mostly built based upon commercially available instruments. To improve the performance of the controller, we have added a custom built frequency converter circuit that matches the modulation frequency of a commercial SQUID sensor and preamplifier. The noise level of the dc SQUID controller system is comparable with a commercial analog system, ~ 4mF0/Ö{Hz} at 100Hz. The current system could control up to 5 SQUID channels.