Low energy electrodynamics of CrI3 layered ferromagnet

Luca Tomarchio; Salvatore Macis; Lorenzo Mosesso; Loi T Nguyen; Antonio Grilli; Mariangela Cestelli Guidi; Robert J Cava; Stefano Lupi

doi:10.1038/s41598-021-02918-4

Low energy electrodynamics of CrI₃ layered ferromagnet

Sci Rep. 2021 Dec 3;11(1):23405. doi: 10.1038/s41598-021-02918-4.

Authors

Luca Tomarchio^{1

2}, Salvatore Macis^{1

3}, Lorenzo Mosesso¹, Loi T Nguyen⁴, Antonio Grilli³, Mariangela Cestelli Guidi³, Robert J Cava⁴, Stefano Lupi^{5

6}

Affiliations

¹ Department of Physics, Sapienza University, Piazzale Aldo Moro 5, 00185, Rome, Italy.
² INFN section of Rome, P.Le Aldo Moro, 2, 00185, Rome, Italy.
³ INFN - Laboratori Nazionali di Frascati, via Enrico Fermi 54, 00044, Frascati, Rome, Italy.
⁴ Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA.
⁵ Department of Physics, Sapienza University, Piazzale Aldo Moro 5, 00185, Rome, Italy. stefano.lupi@roma1.infn.it.
⁶ INFN - Laboratori Nazionali di Frascati, via Enrico Fermi 54, 00044, Frascati, Rome, Italy. stefano.lupi@roma1.infn.it.

Abstract

We report on the optical properties from terahertz (THz) to Near-Infrared (NIR) of the layered magnetic compound CrI₃ at various temperatures, both in the paramagnetic and ferromagnetic phase. In the NIR spectral range, we observe an insulating electronic gap around 1.1 eV which strongly hardens with decreasing temperature. The blue shift observed represents a record in insulating materials and it is a fingerprint of a strong electron-phonon interaction. Moreover, a further gap hardening is observed below the Curie temperature, indicating the establishment of an effective interaction between electrons and magnetic degrees of freedom in the ferromagnetic phase. Similar interactions are confirmed by the disappearance of some phonon modes in the same phase, as expected from a spin-lattice interaction theory. Therefore, the optical properties of CrI₃ reveal a complex interaction among electronic, phononic and magnetic degrees of freedom, opening many possibilities for its use in 2-Dimensional heterostructures.