Although discovered many decades ago, superconductivity in doped ${\mathrm{SrTiO}}_3$ remains a topic of intense research. Recent experiments revealed that, upon increasing the carrier concentration, multiple bands cross the Fermi level, signaling the onset of Lifshitz transitions. Interestingly, $T_c$ was observed to be suppressed across the Lifshitz transition of oxygen-deficient ${\mathrm{SrTiO}}_3$; a similar behavior was also observed in gated ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interfaces. Such a behavior is difficult to explain in the clean theory of two-band superconductivity, as the additional electronic states provided by the second band should enhance $T_c$. Here, we show that this unexpected behavior can be explained by the strong pair-breaking effect promoted by disorder, which takes place if the interband pairing interaction is subleading and repulsive. A consequence of this scenario is that, upon moving away from the Lifshitz transition, the two-band superconducting state changes from opposite-sign gaps to same-sign gaps.

中文翻译：

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SrTiO3和LaAlO3 / SrTiO3界面中的非常规多带超导性

尽管几十年前被发现，但掺杂中的超导性 ${\mathrm{钛酸锶}}_3$仍然是一个深入研究的话题。最近的实验表明，在增加载流子浓度后，多个带穿过费米能级，这标志着Lifshitz转变的开始。有趣的是，${Ť}_C$ 观察到在缺氧的Lifshitz过渡过程中被抑制 ${\mathrm{钛酸锶}}_3$; 在门控系统中也观察到了类似的行为${\mathrm{拉铝}}_3/{\mathrm{钛酸锶}}_3$接口。这种现象很难用干净的两带超导理论来解释，因为第二个带提供的附加电子态应增强${Ť}_C$。在这里，我们表明，这种意外行为可以用无序促进的强大的成对打破效应来解释，如果带间配对相互作用是亚引导和排斥的，就会发生这种情况。这种情况的结果是，在离开Lifshitz跃迁后，两带超导状态从相反符号的间隙变为相同符号的间隙。