Probing inhomogeneous superconductivity with terahertz photon echoes

Conventionally, inhomogeneous superconductivity is probed using scanning tunneling microscopy, which resolves the superconducting gap in space. Such techniques, in particular Josephson tunneling techniques that isolate the superconducting response, are limited, however, to low temperatures which precludes measurement of the superconducting phase transition and possible pseudogap physics. In this talk, I will discuss recent experiments applying 2-D terahertz spectroscopy [1] of the Josephson tunneling resonance to measure inhomogeneities in optimally-doped La_2-xSr_xCuO₄. The resultant photon echo spectra exhibit clear signatures of disorder, which agrees with previous STM measurements of the superconducting gap inhomogeneities and is observed to remain constant as temperature increases towards the superconducting phase transition [2]. I will conclude with an outlook on applying these multidimensional terahertz probes toward resolving disorder in non-equilibrium light-induced states in quantum materials.

[1] Albert Liu, arXiv:2409.03719

[2] Albert Liu et al., Nat. Phys. (2024)