with [111] magnetic field*

The pyrochlore magnet Tb₂Ti₂O₇ has shown exotic magnetic properties and has been considered to be a quantum spin liquid. Although Tb₂Ti₂O₇ has been studied for decades, low energy experiments with magnetic field along [111] are rare. We perform time-domain terahertz spectroscopy on high quality Tb₂Ti₂O₇ crystal to study the crystal field excitations as a function of magnetic field with very high resolution. The excitations behaves significantly different below and above a critical field, indicating a phase transition around 2.5 T. We also observed the discrepancy between two polarization channels. Our work provides insight into this very intriguing material.