I will explain how the application of an old technique from NMR to solid state spectroscopy can yield new insights into the behavior of quantum materials. The technique in question is two dimensional coherent spectroscopy (2DCS). I explain how this technique works, and how it can reveal information inaccessible to other probes. I then discuss how this `new’ experimental technique can be used to glean new insights into a very old problem in solid state physics: decoherence in phosphorous doped silicon. I present experimental results on P doped Si obtained by the Armitage group, and discuss what may be inferred therefrom. I argue that these results indicate a qualitatively new phenomenology for the electronic sector, which we dub `marginal Fermi glass.’ If time permits I may also explain how 2DCS can be useful in other contexts e.g. for unambiguous spectroscopic identification of gapped spin liquids and fracton phases.
Reference: Mahmood, Chaudhury, Gopalakrishnan, Nandkishore and Armitage, arXiv: 2005.10822