Tunneling and transport properties of superconductors

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:106823

Tralshawala, N

We obtained the electron-phonon spectral function, {alpha}{sup 2}F({omega}), from our tunneling data on Ba{sub 1-x}K{sub x}BiO{sub 3} (BKBO) and Nd{sub 2-x}Ce{sub x}CuO{sub 4-y} (NCCO). The analysis is novel in its utilization of tunneling {alpha}{sup 2}F({omega}) function to estimate the contribution to resistivity from the electron-phonon scattering. We tested this methodology for conventional superconductors Nb, V, and VN. We make a strong case for the phonon-mediated coupling in BKBO. We show that phono-mediated coupling plays a major role in the superconductivity of NCCO. Tunneling data on BKBO exhibit a BCS gap and this ratio 2{Delta}/k{sub B} T{sub c} (of about 3.9) corresponds to a moderately coupled superconductor. The tunneling {alpha}{sup 2}F({omega}) compares well with the phonon density of states obtained from the inelastic neutron scattering data; and the T{sub c} calculated from the tunneling {alpha}{sup 2}F({omega}) matches well with the measured value. We explain the resistivity of BKBO using the tunneling {alpha}{sup 2}F({omega}). The high-T{sub c} (about 27 K), the low {lambda} value (about 1), and the fact that optical phonons contribute heavily to the higher T{sub c} suggests that a deeper physical understanding of BKBO is needed to understand the high-T{sub c} cuprates. NCCO is a moderate T{sub c} cuprate superconductor that also shares the presence of spin density wave instability with other cuprates. But NCCO is electron-doped. The gap region tunneling data is distinctly non-BCS-like, but nevertheless we can obtain {alpha}{sup 2}F({omega}), which compares well with the phonon density of states and can explain the measured T{sub c}. We show that NCCO is also moderately coupled with stronger coupling to the optical phonons. Our analysis allows the identification of a T{sup 2} contribution to the resistivity of NCCO and establishes a connection between variations in the magnitude of this contribution and the plasma frequency {omega}{sub p}.

• Research Organization: Illinois Inst. of Tech., Chicago, IL (United States)
• OSTI ID: 106823
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
66 PHYSICS
BARIUM OXIDES
CERIUM OXIDES
COPPER OXIDES
ELECTRON-PHONON COUPLING
HIGH-TC SUPERCONDUCTORS
NEODYMIUM OXIDES
POTASSIUM OXIDES
SUPERCONDUCTIVITY
TRANSITION TEMPERATURE