Probing quantum materials: Nonlinear THz spectroscopy

Abstract:

Non-linear THz spectroscopy has developed into a sensitive and effective method to probe electrodynamics and electronic properties of quantum materials. Very efficient THz high-harmonic generation in Dirac materials, such as graphene [1] and the 3D Dirac semimetal Cd3As2 [2], has been reported, originating from the linear dispersion in these materials. In superconductors, coupling of the THz field to the Higgs mode also leads to a pronounced non-linear THz response [3], as does the non-Fermi liquid state in CaRuO3 [4]. Apart from high-harmonic generation, the non-linear THz response can
also provide insights into the coupling between for instance magnons and phonons in magnetically ordered materials, as is for instance found in antiferromagnetic CoF2 [5]. This contribution will present some of the recent achievements in this field, and discuss the underlying mechanisms leading to the non-linear THz response.    
 
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[2] S. Kovalev, R.M.A. Dantas, S. Germanskiy, et al., Nat. Comm. 11, 2451 (2020).
[3] R. Shimano and N. Tsuji, Annu. Rev. Condens. Matter Phys. 11, 103 (2020).
[4] C. Reinhoffer, S. Esser, S. Esser, et al., Phys. Rev. Lett. 132, 196501 (2024).
[5] T.W.J. Metzger, K.A. Grishunin, C. Reinhoffer, et al., Nat. Comm. 15, 5472 (2024).