Principles of two-dimensional terahertz spectroscopy of collective excitations: The case of Josephson plasmons in layered superconductors

Abstract

This paper presents a theoretical framework for two-dimensional terahertz spectroscopy (2DTS) of collective excitations in condensed matter systems. Focusing on the Josephson plasma resonance in layered superconductors as a model collective excitation, the authors show how 2DTS reveals physics beyond what is accessible in the linear response. They also demonstrate that 2DTS spectra of collective modes can exhibit unique signatures that defy intuition from nuclear magnetic resonance, which may indicate, for example, the presence of dynamics beyond the mean-field approximation.