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arXiv 1012.5333cond-mat.supr-concond-mat.str-el
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强耦合电子-声子系统中可能的奇频超导

Possible Odd-Frequency Superconductivity in Strong-Coupling Electron-Phonon Systems

Hiroaki Kusunose, Yuki Fuseya, Kazumasa Miyake

摘要:

讨论了强耦合电子-声子系统中奇频配对的可能性。利用哈伯德模型,我们证明了频率为$ω_{\rm E}\llω_{c}$($ω_{c}$是重整化带宽的阶数)的软爱因斯坦模介导s波奇频三重态配对对普通偶频单重态配对。奇频配对的出现需要配对相互作用和强耦合一样被强烈阻滞,因为奇频配对的配对相互作用仅在对角散射通道中有效,$(ω_{n},-ω_{n})\to(ω_{n'},-ω_{n'})$与$ω_{n'}=ω_{n}\gtrsim ω_{\rm E}$。也就是说,奇频超导是在与原来BCS理论相反的极限下实现的。强耦合区的Ginzburg-Landau分析表明,与BCS值相比,比热不连续性和超流密度随温度变化的斜率可以很小,这取决于转变温度$T_{c}$和$ω_{c}$的比值.

英文摘要:

A possibility of the odd-frequency pairing in the strong-coupling electron-phonon systems is discussed. Using the Holstein-Hubbard model, we demonstrate that the anomalously soft Einstein mode with the frequency $ω_{\rm E}\llω_{c}$ ($ω_{c}$ is the order of the renormalized bandwidth) mediates the s-wave odd-frequency triplet pairing against the ordinary even-frequency singlet pairing. It is necessary for the emergence of the odd-frequency pairing that the pairing interaction is strongly retarded as well as the strong coupling, since the pairing interaction for the odd-frequency pairing is effective only in the diagonal scattering channel, $(ω_{n},-ω_{n})\to(ω_{n'},-ω_{n'})$ with $ω_{n'}=ω_{n}\gtrsim ω_{\rm E}$. Namely, the odd-frequency superconductivity is realized in the opposite limit of the original BCS theory. The Ginzburg-Landau analysis in the strong-coupling region shows that the specific-heat discontinuity and the slope of the temperature dependence of the superfluid density can be quite small as compared with the BCS values, depending on the ratio of the transition temperature $T_{c}$ and $ω_{c}$.

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