Title: Direct measurement of coherent nodal and antinodal dynamics in underdoped Bi-2212 Show Chinese title

Title: 直接测量欠掺杂Bi-2212中相干节点和反节点动力学

Abstract: The physics of strongly correlated materials is deeply rooted in electron interactions and their coupling to low-energy excitations. Unraveling the competing and cooperative nature of these interactions is crucial for connecting microscopic mechanisms to the emergence of exotic macroscopic behavior, such as high-temperature superconductivity. Here we show that polarization-resolved multidimensional coherent spectroscopy (MDCS) is able to selectively drive and measure coherent Raman excitations in different parts of the Fermi surface, where the superconducting gap vanishes or is the largest (respectively called Nodal and Antinodal region) in underdoped Bi-2212. Our evidence reveal that in the superconducting phase, the energy of Raman excitations in the nodal region is anti-correlated with the energy of electronic excitations at $\sim$1.6~eV, and both maintain coherence for over 44~fs. In contrast, excitations in the antinodal region show significantly faster decoherence ($<$18~fs) and no measurable correlations. Importantly, this long-lived coherence is specific to the superconducting phase and vanishes in the pseudogap and normal phases. This anti-correlation reveals a coherent link between the transition energy associated with the many body Cu-O bands and the energy of electronic Raman modes that map to the near-nodal superconducting gap. The different coherent dynamics of the nodal and antinodal excitations in the superconducting phase suggest that nodal fluctuations are protected from dissipation associated with scattering from antiferromagnetic fluctuations and may be relevant to sustaining the quantum coherent behaviour associated with high temperature superconductivity. Show Chinese abstract

Abstract: 强关联材料的物理性质深深植根于电子相互作用及其与低能激发的耦合。 揭示这些相互作用的竞争与协同性质对于将微观机制与奇异宏观行为的出现联系起来至关重要，例如高温超导性。 在这里，我们展示了偏振分辨的多维相干光谱学（MDCS）能够选择性地驱动和测量费米面上不同区域的相干拉曼激发，其中超导能隙消失或最大（分别称为节点区和反节点区）在欠掺杂的Bi-2212中。 我们的证据表明，在超导相中，节点区的拉曼激发能量与电子激发在$\sim$1.6~eV 处的能量呈反相关，并且两者在超过44~fs的时间内保持相干性。 相反，反节点区的激发表现出显著更快的退相干（$<$18~fs）且没有可测量的相关性。 重要的是，这种长寿命的相干性仅存在于超导相，并在赝能隙相和正常相中消失。 这种反相关性揭示了与多体Cu-O带相关的跃迁能量与映射到近节点超导能隙的电子拉曼模态能量之间的相干联系。 超导相中节点和反节点激发的不同相干动力学表明，节点涨落受到保护，免受来自反铁磁涨落散射的耗散影响，并可能与维持高温超导性相关的量子相干行为有关。