Electron Tunneling Spectroscopic Measurements on Al-doped MgB₂ Thin Films

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• 作者：A.G. Zaitsev ; R. Schneider ; O. de la Pe-a-Seaman ; R. de Coss ; R. Heid ; K.-P. Bohnen ; J. Geerk
• 关键词：Magnesium diboride ; superconducting thin films ; tunneling spectroscopy ; electron-phonon coupling
• 刊名：Physics Procedia
• 出版年：2012
• 出版时间：2012
• 年：2012
• 卷：36
• 期：Complete
• 页码：479-484
• 全文大小：246 K

文摘

The effect of Al-doping on the electron-phonon coupling in magnesium diboride films was studied by electron tunneling spectroscopy on planar sandwich-type Mg1-xAlxB2-oxide-indium junctions. The superconducting Mg1-xAlxB2 films (0 ¡Ü x < 0.5) were prepared in situ by simultaneous sublimation of Mg and sputtering of B and Al. The oxide barrier was either natural or artificial (aluminium oxide). The high junction quality allowed precise measurements of the differential conduction up to high bias-voltages of 120 mV. In the low bias range the small energy gap ¦¤¦Ð was measured: it decreased linearly with increasing Al-doping in agreement with the band filling model. The measurements at higher energies revealed the phonon induced features in the electron density of states. Although the spectra were influenced by the proximity effect below ¡«20meV, they enabled the determination of the effective Eliashberg function ¦Á²F. For the same film compositions ¦Á²F data were obtained theoretically from first principles calculations. The progressive loss of superconductivity with increasing Al doping was reflected in both the experiment and calculations by the evolution of ¦Á²F. The dominating ¦Ð-¦Ò interband pairing interaction, which contributes most to the superconductivity on the ¦Ð sheet, was gradually weakened in correlation with the band structure calculations.