Low energy electrodynamics of triangular lattice quantum spin liquid candidate YbMgGaO$_{4}$

Quantum spin liquids (QSL) are exotic magnetic states where spins do not order down to the lowest temperatures. Spin 1/2 two-dimensional triangular antiferromagnet YbMgGaO$_{4}$ is a promising QSL candidate. Here we report an optical measurement on YbMgGaO$_{4}$ using time domain terahertz spectroscopy (TDTS)and Fourier transform spectroscopy (FTIR). We find the real part of in-plane dissipative response shows a power law behavior that may arise from spin liquid properties. Applying magnetic field in the Faraday geometry, we approach the spin polarized state from which we can extract g-factors and determine exchange constants quantitatively. We also identify a crystal field excitation in the infrared measurement. Our results provide guidance for the future theoretical study of this QSL.