UC Berkeley

Transition metal compounds have long been known to host intriguing many-body ground states owing to a fine interplay between electron-electron interactions, electron-phonon coupling, and low dimensionality. Recent advances in van der Waals synthesis have enabled the experimental studies of transition metal dichalcogenides in the extreme two-dimensional limit. In this dissertation I will discuss experiments that probe novel many-body ground states in single-layer transition metal dichalcogenides via the use of scanning tunneling microscopy and spectroscopy (STM/STS). The first part of the dissertation focuses on charge density wave states in single-layer 1H-NbSe2, single-layer 1H-TaSe2, and single-layer 1T-TaSe2 and the mechanisms by which they arise. The second part of the dissertation discusses an exotic Mott insulator electronic ground state in single-layer 1T-TaSe2 and its collapse with increased temperature and/or the introduction of interlayer coupling. In the third part of the dissertation I present evidence supporting a novel many-body magnetic ground state called a quantum spin liquid in the spin channel of single-layer 1T-TaSe2. This gapless spin liquid state was probed by spectroscopic STM imaging as well as by its response to single magnetic impurities. The results discussed here establish new platforms for investigating correlation physics in two dimensions and provide insights into the intriguing many-body phases therein.