Fig. 2: Phase-matching resolves individual plasmon nonlinearities.
From: Probing inhomogeneous cuprate superconductivity by terahertz Josephson echo spectroscopy
a, A schematic of wavevector phase-matching, in which momentum is only conserved along the in-plane (∥) direction and in its magnitude |kfp|. b, Sample rotation changes the in-plane momenta of each excitation field and determines the nonlinearity that arrives at the detector. c, Experimental measurements of the constituent components of χφ(3) in La1.83Sr0.17CuO4 are shown with the corresponding sample rotation angles. The (ft, fτ) = (2, ±2) THz peaks are measured with EB arriving first, followed by EA. The (2, 0) and (2, 4) THz peaks are measured with EA arriving first, followed by EB. The (2, −2) THz peak corresponds to an emitted Josephson echo. The full phase-matching conditions for both time orderings are described in Supplementary Section 2.
