Prof. Theodore H. Geballe Profile

Prof. Theodore H. Geballe

at Stanford Univ

SPIE Involvement:

Author

Proceedings Article | 30 August 2005 Paper

Evidence for charge Kondo effect in superconducting Tl-doped PbTe

I. Fisher, Y. Matsushita, H. Bluhm, T. Geballe

Proceedings Volume 5932, 59321Y (2005) https://doi.org/10.1117/12.620179

KEYWORDS: Thallium, Superconductivity, Tellurium, Lead, Crystals, Electrons, Superconductors, Magnetism, Ions, Germanium

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Proceedings Article | 30 August 2005 Paper

Discovering superconductors: A path to new science and higher Tc's

T. Geballe, Gertjan Koster

Proceedings Volume 5932, 59321S (2005) https://doi.org/10.1117/12.626120

KEYWORDS: Superconductors, Superconductivity, Ions, Copper, Thallium, Mercury, Oxygen, Particles, Doping, Physics

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Proceedings Article | 1 March 1991 Paper

Structural and electrical properties of epitaxial YBCO films on Si

David Fork, A. Barrera, Julia Phillips, N. Newman, David Fenner, Theodore Geballe, G.A. Connell, James Boyce

Proceedings Volume 1394, (1991) https://doi.org/10.1117/12.25748

KEYWORDS: Silicon, Ions, Resistance, Zirconium dioxide, Laser processing, Pulsed laser deposition, Crystals, Barium, Technetium, Niobium

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Efforts to grow high quality films of YBCO on Si have been complicated by factors discussed in Ref. 1, chief among them being the reaction between YBCO and Si, which is damaging even at 550 C. This is well below the customary temperatures for YBCO film growth. To avoid the reaction problem, epitaxial YBCO films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ).2 Both layers are grown via an entirely in situ process by pulsed laser deposition (PLD). Although the buffer layer prevents reaction, another problem arises; the large difference in thermal expansion coefficients between silicon and YBCO causes strain at room temperature. Thin (<500 A) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Thicker films are cracked and have poorer electrical properties. The thermal strain may be reduced by growing on silicon-on-sapphire (SOS) rather than silicon.3 This allows the growth of films of arbitrary thickness. Ion channeling reveals a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12% on either silicon or SOS. The normal state resistivity is 250-300 i-cm at 300 K; the critical temperature, Tc (R=0), is 86-88 K with a transition width (ATc) of I K. Critical current densities (J)°f 2x107 A/cm2 at 4.2 K and >2x106 A/cm2 at 77 K have been achieved. In addition, the surface resistance of a YBCO film on SOS was measured against Nb at 4.2 K. At 10 GHz, a value of 45 was obtained. This compares favorably to values reported for LaAlO3. Application of this technology to produce reaction patterned microstrip lines has been tested.4 This was done by ion milling away portions of the YSZ buffer layer prior to the YBCO deposition. YBCO landing on regions of exposed Si reacts to form an insulator. This technique was used to make 3 micron lines 1.5 mm long. The resulting structure had a Jc of l.6xl06 A/cm2 at 77 K. Isolation of separate structures exceeded 20 M. Several advantages of this technique are that no solvents, etchants or photoresist come into contact with the YBCO, hence this technique has a potential for operational-asgrown devices. In summary, it is now possible to produce YBCO films with structural and DC electrical properties which rival the most optimized c-axis epitaxial YBCO films on MgO, SrTiO3 and LaAlO3. Preliminary measurements of microwave properties appear promising. We thank Bruce Lairson for help obtaining magnetization data and Richard Johnson, Steve Ready and Lars-Erik Swartz for technical assistance. This work benefits from AFOSR (F49620-89-C-0017). DBF received support from NSF (DMR- 8822353). DKF acknowledges the AT&T scholarship.

Proceedings Article | 1 October 1990 Paper

Preparation and high-frequency properties of high Tc superconducting thin films

Chang-Beom Eom, Theodore Geballe

Proceedings Volume 1287, (1990) https://doi.org/10.1117/12.20890

KEYWORDS: Superconductors, Technetium, Thin films, Multilayers, Sputter deposition, Resistance, Superconductivity, Barium, Crystals, Modulation

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Conference Committee Involvement (1)

Strongly Correlated Electron Materials: Physics and Nanoengineering

31 July 2005 | San Diego, California, United States

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