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Terahertz magneto-optical investigation of quadrupolar spin-lattice effects in magnetically frustrated Tb₂Ti₂O₇

It is quite uncommon to find magnetic materials that do not freeze in one way or another at very low temperature. This is the case for Tb₂Ti₂O₇, where the pyrochlore lattice of interconnected tetrahedra displays novel perpetually fluctuating magnetic behavior that remains enigmatic. Here, we employ THz spectroscopy that can probe dynamics in the frequency range relevant to both the magnetism and lattice. Supported by magneto-optical quantum calculations, we validate a model of spin-lattice coupling that drives the complex dynamic magnetism in this frustrated material. Consequently, we also demonstrate a new type of magneto-optical activity in the THz range.