发表机构
Max Planck Institute for Solid State Research; University of Tokyo; Cryogenic Research Center, University of Tokyo; RIKEN Center for Emergent Matter Science (CEMS); Trans-scale Quantum Science Institute, University of Tokyo（马克斯·普朗克固体研究所; 东京大学; 东京大学低温研究中心; 理化学研究所涌现物质科学中心; 东京大学跨尺度量子科学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该理论工作证明太赫兹二维相干光谱可通过边带发射直接指纹化多带超导体中的Leggett模式，无需预知频率或调参，且对温度和弛豫鲁棒，扫描脉冲中心频率可无歧义识别该模式。
AI 中文摘要
超导凝聚体的集体模式编码了配对相互作用的基本信息，然而其直接探测在实验上仍具挑战性。在多带超导体中，Leggett模式，即两个凝聚体之间相对相位的相干振荡，具有拉曼活性，但在通常情形下仅以非线性方式与光耦合。在此，我们从理论上证明，太赫兹二维相干光谱（2DCS）通过非线性二维光谱中检测频率ω_t = ω_L±Ω（Ω为入射脉冲的中心频率）处的边带发射，为Leggett模式（频率为ω_L）提供了直接指纹。关键见解在于，太赫兹脉冲的有限持续时间是使该模式可被观测的物理机制：有限脉冲的宽频谱内容提供了所需的非线性频率组合，无需预先知道其数值或调节外部参数即可在ω_L处共振激发该模式。我们展示了该特征对温度和准粒子弛豫的鲁棒性，并表明扫描Ω能够无歧义地识别Leggett模式。
英文摘要
Collective modes of the superconducting condensate encode fundamental information on the pairing interaction, yet their direct detection remains experimentally challenging. In multiband superconductors, the Leggett mode, i.e., a coherent oscillation of the relative phase between two condensates, is Raman-active and couples to light only nonlinearly in ordinary situations. Here we show theoretically that terahertz two-dimensional coherent spectroscopy (2DCS) provides a direct fingerprint of the Leggett mode (with frequency $ω_L$) through sideband emission at the detection frequency $ω_t = ω_L\pmΩ$ ($Ω$ is the central frequency of the incident pulses) in the nonlinear 2D spectrum. The key insight is that the finite duration of the THz pulses is the physical mechanism that makes the mode accessible: the broad spectral content of a finite pulse provides the nonlinear frequency combinations needed to resonantly excite the mode at ωL without any prior knowledge of its value or tuning of external parameters. We demonstrate robustness of this signature against temperature and quasiparticle relaxation, and show that sweeping $Ω$ allows unambiguous identification of the Leggett mode.
Comments14 pages, 11 figures
