Correlation spectroscopy of exchange interactions in rare-earth doped garnets

Multi-dimensional nonlinear spectroscopy is a very powerful tool that bears the potential to unravel the dynamics (both coherent and incoherent) and coupling of elementary interactions in solid-state systems. Due to low THz photon energies (approx. 4 meV at 1THz), these radiations provide a means to address electronic states by resonant excitation and detection of electronic states having energy differences in the meV range. Typically, intense THz pulses have the potential to induce ultrafast electric- or magnetic-switching operations that last from a few tens of femtoseconds to a few tens of picoseconds. With the advancement for the generation and detection of intense THz pulses, researchers have started exploring THz-driven nonlinear phenomena in a wide class of material systems in the last few years. For example, observation of second-order nonlinearities in undoped single-domain LiNbO3crystals [1], observation of multiple harmonics and quantum coherences in semiconductor systems [2] and canted antiferromagnets [3] like YFeO3.Further, both energy and time scales of THz radiation favors fundamental investigations on magneto-optical interplay at the quantum level, thus fostering all-optical control of magnetic writing for spintronic applications. Garnets, in particular, provide a platform towards the development of technologically relevant material for magneto-optical spintronic devices. On doping with rare-earth elements (like Gd and Yb), these garnets show an unusual strong excitation of magnetization precession with a frequency in the THz regime [4]. This resonance is termed as exchange resonance because of the exchange interaction between rare-earth and transition metal elements. In my talk, I will present our observations on the nonlinear magneto-optical interaction via two-dimensional THz correlation spectroscopy [5].

[1] 	C. Sommaet al., Phys. Rev. Lett.112, 146602 (2014).
[2] 	S. Markmann, H. Nong, S. Palet al., Opt. Express25, 21753 (2017).
[3] 	J. Luet al., Phys. Rev. Lett.118, 207204 (2017).
[4] 	S. Parchenkoet al., Appl. Phys. Lett.108, 032404 (2016).
[5] 	S. Palet al., CLEOQELS (2019), https://doi.org/10.1364/CLEOQELS.2019.FM3D.3.