AI 中文总结
该研究在Nambu-Keldysh准经典框架中，揭示了超导体中希格斯与BS模式的有限动量耦合机制，发现干净极限下二者无避免交叉，脏极限下无序可诱导避免交叉，耦合决定杂化支劈裂，具有实验意义。
AI 中文摘要
在具有竞争配对通道的超导体中，对破缺边以下存在两种明确定义的激发：主导s波通道的希格斯模式，以及次主导d波通道的巴尔达西斯-施里弗（BS）激子。它们的混合受到双重禁止：零动量下受点群对称性限制，且二者分别处于序参量的振幅和相位扇区，在任意动量下受粒子-空穴对称性限制。我们在扩展至领头阶1/ε_F修正并包含自洽屏蔽库仑势的Nambu-Keldysh准经典框架中，证明有限动量结合粒子-空穴不对称会产生直接耦合，且可得到其闭式表达式。然而，该耦合是否产生避免交叉并非由其大小决定，而是由运动学条件决定。在干净极限下，希格斯模式并非亚能隙极点，而是钉扎在对破缺边的共振，其色散系数在(v_F q)²中为1，而束缚BS模式的色散更慢；因此两支分离而非收敛，永不会简并。该阻碍是干净极限特有的：精确的脏极限结果显示，无序会使振幅共振脱离对破缺边并反转其色散，这可在中等散射下导致其与BS模式出现避免交叉；在该区域，本文计算的耦合将决定杂化支之间的劈裂。我们讨论了这些结果的实验意义。
英文摘要
In superconductors with competing pairing channels, two well defined excitations exist below the pair-breaking edge: the Higgs mode of the condensed $s$-wave channel and the Bardasis--Schrieffer (BS) exciton of the subdominant $d$-wave channel. Their mixing is doubly forbidden --- by point-group symmetry at zero momentum and because the two reside in the amplitude and phase sectors of the order parameter respectively, by particle--hole symmetry at every momentum. Working in a Nambu--Keldysh quasiclassical framework extended to leading $1/\varepsilon_F$ corrections and including the self-consistently screened Coulomb potential, we show that finite momentum combined with particle--hole asymmetry generates a direct coupling which we obtain in closed form. Whether this coupling produces an avoided crossing is decided, however, not by its magnitude but by kinematics. In the clean limit the Higgs is not a sub-gap pole but a resonance pinned to the pair-breaking edge, which disperses with coefficient unity in $(v_Fq)^2$, while the bound BS mode disperses more slowly: the two branches therefore separate rather than converge and never become degenerate. The obstruction is specific to the clean limit: exact dirty-limit results show that disorder detaches the amplitude resonance from the edge and reverses its dispersion, which can result in an avoided crossing with the BS mode at intermediate scattering. In that regime, the coupling computed here would set the splitting between the hybridized branches. We discuss the experimental implications of these results.
Comments16 pages, 5 figures
