Two-dimensional coherent spectroscopy: concepts and opportunities for strongly-correlated electronic systems
Two-dimensional coherent spectroscopy (2DCS) is a powerful experimental technique that probes the nonlinear optical response of materials. In essence, the traditional “1D” spectroscopy, which measures the linear response, reveals the excitations in a system, whereas the 2DCS unveils the interplay between these excitations. The 2DCS in the infrared frequency range has been widely used in chemistry and biology to unravel the complex structure of molecules. The advent of tetrahertz 2DCS makes it now possible to apply this technique to solid state systems and, in particular, strongly correlated electronic systems. In this talk, I will give an exposition to the basic concepts of the 2DCS and demonstrate theoretically its potential utilities in quantum spin systems. Specifically, I will show that the 2DCS can resolve the “spinon continuum” from the gapped fractional excitations. For the Luttinger spin liquid, the 2DCS can directly reveal the coherent propagation of the fractional excitations.