W S Chu et al 2009 New J. Phys. 11 083005 doi:10.1088/1367-2630/11/8/083005
Local lattice dynamics and isotope effect in yttrium diboride probed by extended x-ray absorption fine structure spectroscopy
W S Chu1,2, A Marcelli3, T D Hu1, S Q Wei2, W H Liu4, N L Saini5, A Bianconi5 and Z Y Wu1,2,6,7
Show affiliationsThe lattice vibration properties and the boron isotope effect have been studied in YB2 by using temperature-dependent extended x-ray absorption fine structure (EXAFS). The data show anomalous behavior of the Debye–Waller factor of the Y–B pair due to the superposition of an optical mode associated with the boron sublattice and an acoustic mode corresponding to the yttrium sublattice. We claim that the observed decoupling between metal and boron vibrations is responsible for the lower transition temperature compared to MgB2. The analysis of the boron isotope effect confirms also that the B–B vibration mode plays a key role in the electron–phonon coupling.
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GENERAL SCIENTIFIC SUMMARY
Introduction and background. In the first decade of the new century, the discovery of superconductivity in MgB2 and more recently in iron-based materials restarted the search for novel high-Tc superconductors (HTSCs) and their superconducting mechanism, one of the most intriguing problems in condensed matter physics. At present, due to the absence of the isotope effect in high-Tc cuprates, a large consensus exists on the electron–electron interaction (EEI) being the key mechanism of superconductivity compared with the classical electron–phonon interaction (EPI) of the BCS theory. The challenging observation of the isotope effect substitution on the Tc in MgB2 and in iron-based superconductors suggests an accurate survey of the contribution of the lattice dynamics on the superconducting behavior of HTSCs.Main results. In this manuscript, we investigated the MgB2-related system YB2, showing how EXAFS (extended x-ray absorption fine structure) spectroscopy is a powerful and almost unique technique capable of investigating the isotope effect and its influence on the local lattice dynamics of superconductors. The analysis allows the lattice vibration to be correlated with the superconductive mechanism in metal diborides and in particular: (a) the decoupling of vibrations between the metal and B atoms is probably the mechanism that leads to the strong decrease of the superconducting critical temperature of YB2 compared to MgB2; (b) the B–B vibrational mode plays a key role in the electron–phonon coupling.
Wider implications. This analysis could also be extended to the newly discovered iron-based superconductors and to high-Tc cuprate superconductors.
- PACS
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78.70.Dm X-ray absorption spectra
- Subjects
- Dates
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Issue 8 (August 2009)
Received 23 April 2009
Published 4 August 2009
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Local lattice dynamics and isotope effect in yttrium diboride probed by extended x-ray absorption fine structure spectroscopy
W S Chu et al 2009 New J. Phys. 11 083005
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