Optical conductivity of single crystals of Ba1?x Mx BiO3 (M=K, Rb, x=0.04, 0.37)

Autor: Michael L. Norton, D. Chandler-Horowitz, V. Browning, Terence J. Wieting, Dale L. Peebles, Soumyendu Guha
Rok vydání: 1993
Předmět:
Zdroj: Journal of Superconductivity. 6:339-349
ISSN: 1572-9605
0896-1107
DOI: 10.1007/bf00617482
Popis: Reflectance data (0.001–4.0 eV) from several large (a typical surface area 3×3 mm2) single crystals of Ba1−x KxBiO3 (x=0.04, 0.37) (BKBO) and Ba1−x,RbxBiO3 (x=0.37) (BRBO) were obtained by Fourier transform infrared (FTIR) and ellipsometric methods. Normal-state optical conductivities (σ1) of these samples were obtained from infrared and ellipsometric measurements using a Kramers-Kronig transform. A broad mid-IR band was observed that peaked at 0.3 eV for BKBO and at 0.16 eV for BRBO at room temperature. Each band was fitted with two Lorentz oscillators. The optical mass of the charge carriers was obtained from a Drude fit, and was found to be large (m= 28−33m e ). These overdamped charge carriers can be viewed as polarons with a large effective mass. An optic phonon mode at 325cm−1 was also observed in the metallic phase. This mode was identified as a disorder-induced lattice mode, and was strongly enhanced at 8 K, favoring a strong coupling between this phonon and itinerant electronic states. Low-frequency spectra between 10 and 400 cm−1 observed below the superconducting temperature indicated an energy gap that agreed with the BCS-type mechanism. Interpretations of low-temperature measurements on BKBO and BRBO were complicated due to the change of color of the sample from bluish-green to bronze-red. Upon warming, samples revert to their original bluish-green color.
Databáze: OpenAIRE
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