Probing amplified Josephson plasmons in YBa 2 Cu 3 O 6+x by multidimensional spectroscopy

Journal article

The nonlinear driving of collective modes in quantum materials can lead to a number of striking non-equilibrium functional responses, which merit a comprehensive exploration of underlying dynamics. However, the coherent coupling between nonlinearly-driven modes frequently involves multiple mode coordinates at once, and is often difficult to capture by one-dimensional pump probe spectroscopy. One example is phonon-mediated amplification of Josephson plasmons in YBa2Cu3O6+x, a phenomenon likely associated with the mysterious superconducting-like optical response observed in this material. Here, we report two-dimensional nonlinear spectroscopy measurements in driven YBa2Cu3O6+x. We excite apical oxygen phonons with pairs of mutually-delayed carrier envelope phase stable mid-infrared pump pulses, and detect time-modulated second-order nonlinear optical susceptibility. We find that the driven phonons parametrically amplify coherent pairs of fluctuating opposite-momentum Josephson plasma polaritons, corresponding to a squeezed state of the Josephson plasma.

Authors: Taherian, N; Först, M; Liu, A; Fechner, M; Pavicevic, D

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Nature Research
• Journal: npj Quantum Materials
• Volume: 10
• Issue: 1
• Article number: 54
• Publication date: 2025-06-06
• Acceptance date: 2025-05-17
• DOI: 10.1038/s41535-025-00776-1
• EISSN: 2397-4648
• Language: English