Phonon mechanism in the most dilute superconductor n-type SrTiO3
Phonon mechanism in the most dilute superconductor n-type SrTiO3
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DOI：
10.1073/pnas.1604145113
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发表时间：
2016-04-26
影响因子：
11.1
通讯作者：
Gor'kov, Lev P.
中科院分区：
文献类型：
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作者：
Gor'kov, Lev P.
半个世纪来一直是个谜的n掺杂SrTiO_3的超导电性被看作是非绝热声子配对的一个特例。受实验的启发，我们建议在某些掺杂浓度的迁移率边缘的存在。光谱的巡游部分由三个连续填充电子的导带组成。每个子带都对超导不稳定性有贡献，并且在低温下在其能谱中表现出间隙。我们认为，n型掺杂SrTiO 3的超导电性是由电子与几个频率远大于费米能的纵向（LO）光学声子相互作用引起的。不动的电荷下的迁移率边缘阈值增加的“光学”介电常数远高于在干净的SrTiO 3放置控制上的电子-LO声子相互作用。T-C最初随着费米面的态密度的增加而增加，但积累的电荷通过屏蔽纵向电场而降低了电子-极化声子相互作用。该理论预测的最大值的T-C-浓度依赖性确实观察到实验。在第三个能带中达到最大值后，转变温度最终降低，使T-C（n）圆顶变圆，随着电子填充连续的能带，三个最大值以及伴随的超导能隙连续出现。这是由于电子的LO光学声子配对的属性。LO声子机制为提高块状过渡金属氧化物和其他极性晶体中的超导转变温度以及LaAaO（3）/SrTiO 3界面和SrTiO 3衬底上的带电二维层中的超导转变温度开辟了道路。
Superconductivity of n-doped SrTiO3, which remained enigmatic for half a century, is treated as a particular case of nonadiabatic phonon pairing. Motivated by experiment, we suggest the existence of the mobility edge at some dopant concentration. The itinerant part of the spectrum consists of three conduction bands filling by electrons successively. Each subband contributes to the superconducting instability and exhibits a gap in its energy spectrum at low temperatures. We argue that superconductivity of n-doped SrTiO3 results from the interaction of electrons with several longitudinal (LO) optical phonons with frequencies much larger than the Fermi energy. Immobile charges under the mobility edge threshold increase the "optical" dielectric constant far above that in clean SrTiO3 placing control on the electron-LO phonon interaction. T-C initially grows as density of states at the Fermi surface increases with doping, but the accumulating charges reduce the electrons-polarphonon interaction by screening the longitudinal electric fields. The theory predicts maxima in the T-C-concentration dependence indeed observed experimentally. Having reached a maximum in the third band, the transition temperature finally decreases, rounding out the T-C (n) dome, the three maxima with accompanying superconducting gaps emerging consecutively as electrons fill successive bands. This arises from attributes of the LO optical phonon pairing of electrons. The mechanism of LO phonons opens the path to increasing superconducting transition temperature in bulk transition-metal oxides and other polar crystals, and in charged 2D layers at the LaAaO(3)/SrTiO3 interfaces and on the SrTiO3 substrates.