通过超声传播异常研究 CeRh$_2$As$_2$ 的序参数
Investigation of CeRh$_2$As$_2$ order parameters via ultrasound propagation anomalies
AI总结：
通过超声传播测量研究 CeRh$_2$As$_2$ 的序参数，发现其超导序参数为单组分，同时相 I 中存在无序磁序参数。
摘要：
非常规超导体具有几乎简并的配对态是罕见的。CeRh$_2$As$_2$ 近来成为少数已知的多相超导体之一。当沿晶格 $c$-轴施加磁场时，它在两种不同的超导态之间表现出一级相变。尽管这种行为已被关联到局部破坏的反演对称性，但基于多组分超导序参数的相图仍是一种可能性。此外，超导性似乎与有序态（相 I）共存。尽管受到许多研究，但关于两个超导相和相 I 中序参数的性质仍知之甚少。在这里，我们利用低温、高磁场和静水压力下的超声传播测量来解决这个问题。我们的结果强烈表明，两个相中的超导序参数是单组分的，证实了局部非中心对称性在 CeRh$_2$As$_2$ 多相超导性发展中的作用。此外，基于 Landau 相变框架对弹性异常的分析强烈表明相 I 中存在无序的磁序参数。
英文摘要：
Unconventional superconductors with nearly degenerate pairing states are rare. CeRh$_2$As$_2$ has recently emerged as one of the few existing multi-phase superconductors. It exhibits a first-order phase transition between two distinct superconducting states when a magnetic field is applied along the crystallographic $c$-axis. While this behavior has been linked to locally broken inversion symmetry, a phase diagram based on a multi-component superconducting order parameter remains a possibility. Furthermore, superconductivity appears to coexist with an ordered state (phase I). Despite being the subject of many studies, little is known about the nature of the order parameters in both superconducting phases and phase I. Here, we use ultrasound-propagation measurements at low temperatures, in high magnetic fields and under hydrostatic pressure to address this issue. Our results strongly suggest that the superconducting order parameter in both phases is single-component, corroborating the role of local non-centrosymmetry in the development of multi-phase superconductivity in CeRh$_2$As$_2$. In addition, analysis of the elastic anomalies within the Landau framework of phase transitions strongly suggests the presence of an incommensurate magnetic order parameter in phase I.
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