Submillimeter residual losses in high-T_c superconductors

Thesis/Dissertation · Wed Sep 01 00:00:00 EDT 1993

DOI:https://doi.org/10.2172/10104731· OSTI ID:10104731

Miller, David ^[1]

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1. Univ. of California, Berkeley, CA (United States)

Bolometry was used obtain accurate submillimeter residual loss data for epitaxial films of YBa₂Cu₃O₇ (YBCO), Tl₂Ca₂Ba₂Cu₃O₁₀, Tl₂CaBa₂Cu₂O₈ (TCBCO), and Ba_0.6K_0.4BiO₃ (BKBO). We were able to fit the absorptivity measured for Nb films to an Eliashberg strong coupling calculation; excellent agreement resulted between parameters from best fits and measured Residual Resistivity Ratio. Microwave surface resistance measurements made on the same YBCO and TCBCO films are in excellent agreement with submillimeter measurements. Absorptivities for all YBCO films studied are qualitatively similar, increasing smoothly with frequency, with no gap-like features below the well known absorption edge at 450 cm^-1. Losses in YBCO films were fit to a weakly coupled grain model for the a-b plane conductivity. Strong phonon structure was observed in TCBCO films between 60 and 700 cm^-1 (2 THz and 23 THz); these losses could not be fitted to the simple weakly coupled grain model, in contrast to the case for other high-T_c superconductors where phonon structure observed in ceramics are is absent in epitaxial oriented films and crystals because of electronic screening due to high conductivity of a-b planes. Absorptivity data for the BKBO films all show a strong absorption onset near the BCS tunneling gap of 3.5 k_BT_c. Comparison with strong coupling Eliashberg predictions and of a Kramers-Kronig analysis indicate that the absorption onset is consistent with a superconducting energy gap. Effects of magnetic field on residual losses in YBCO films show a resonant absorption feature in vicinity of predicted

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10104731
• Report Number(s): LBL-34665; ON: DE94003241
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: Sep 1993
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
HIGH-TC SUPERCONDUCTORS
LOSSES
NIOBIUM
KRAMERS-KRONIG CORRELATION
EPITAXY
SUPERCONDUCTING FILMS
BOLOMETERS
INFRARED RADIATION
ABSORPTION
YTTRIUM OXIDES
BARIUM OXIDES
COPPER OXIDES
THALLIUM OXIDES
CALCIUM OXIDES
BISMUTH OXIDES
POTASSIUM OXIDES
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