Physics – Condensed Matter – Superconductivity
Scientific paper
2011-10-26
Physics
Condensed Matter
Superconductivity
5-page main text plus 4-page supplementary material
Scientific paper
The microscopic origin of superconductivity has been established in numerous classes of materials. In elemental metals it results from the exchange of phonons whereas in copper oxides and iron pnictides it is intimately connected to magnetism. On the other hand, the cause of superconductivity in Ba$_{1-x}$K$_x$BiO$_3$ ($T_c$ =32 K)[1] and a large third class of isotropic high temperature superconductors is still mysterious and subject of debate.[2] Proposed mechanisms in bismuthates involve either the tendency of the Bi atoms avoiding the Bi$^{4+}$ state, while preferring the Bi$^{3+}$ and Bi$^{5+}$ charge state thus generating an attractive local "negative U" pairing center[3,4], or strong coupling to an O-breathing phonon mode[5,6]. However, first principles calculations have so far ruled out both the negative U mechanism[7,8] and the electron-phonon mechanism[9]. Here we demonstrate that dynamical correlations among electrons enhance their coupling to phonons in a large number of superconductors, raising significantly the previously underestimated theoretical superconducting critical temperature T$_c$ of up to a few Kelvin to their experimental values of tens of Kelvin. The mechanism we propose is quite general, explains the magnitude and the doping dependence of superconductivity in many materials such as the celebrated Ba$_{1-x}$K$_x$BiO$_3$ compounds and the electron-doped $\beta$-HfNCl compounds ($T_c$ = 25.5 K)[10] and can be used to design other high temperature superconductors which have not yet been synthesized. As an application, we suggest Ba$_{1-x}$La$_x$PbO$_3$ with $x\sim$0.7 will superconduct above 10 K.
Kotliar Gabriel
Kutepov Andrey
Yin Z. P.
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