Probing Cuprate Superconductivity with Nonlinear THz Spectroscopy

Nonlinear THz spectroscopy provides a new window into the low-energy electrodynamics of complex materials. In superconductors, it allows for the measurement of higher-order correlation functions that are not accessible through linear probes.

In high-Tc cuprate superconductors, the odd-order nonlinear optical susceptibilities are especially pronounced along the c-axis, where Josephson tunneling dominates the response [1]. In this talk, I will present our recent angle-resolved two-dimensional THz spectroscopy (2DTS) experiment on optimally doped La₂₋ₓSrₓCuO₄. I will discuss how these measurements enable an assessment of finite momentum fluctuations of the superconducting order parameter [2].

[1] Laplace, Y., & Cavalleri, A. (2016). Josephson plasmonics in layered superconductors. Advances in Physics: X, 1(3), 387–411

[2] Gómez Salvador, A., et al. (2024). Principles of two-dimensional terahertz spectroscopy of collective excitations: The case of Josephson plasmons in layered superconductors. Phys. Rev. B, 110(9), 094514