Electrodynamics of MnBi2Te4 intrinsic magnetic topological insulators


We report on the electrodynamics of MnBi2Te4 thin films, an intrinsic magnetic topological material. We study its optical conductivity from terahertz (THz) to ultraviolet (UV) frequencies as a function of the film thickness, highlighting the presence of surface topological states superimposed on the bulk electrodynamics response. For the thinnest film, where the charge transport is dominated by Dirac surface states, we investigate the effect of the phase transition from the high-temperature topological protected state to the low-temperature magnetic (time-reversal broken) state by measuring the optical conductivity across the Néel temperature. At low temperatures, the breaking of the time reversal symmetry affects the optical conductivity, indicating that a magnetic-induced gap opens below TN.





Fig. 1 Optical spectroscopy of MBT thin films. a) View of the crystal structure of MnBi2Te4. The Bi, Te and Mn atoms are bonded to form a septuple layer structure, with an antiferromagnetic exchange between the Mn layers. The arrows indicate the crystal axes. The dotted lines highlight the unit cell. b)  Schematic description of the thin film samples over an HRFZ-Si(111) substrate. The two surfaces are expected to host Dirac states due to the nontrivial topology of the bulk gapped bands. c) Experimental transmittance of MBT films over a silicon substrate. The black curves correspond to a Drude-Lorentz fitting (see main text) on the transmittance of the bare Si substrate (black points) and on the 7 SL film (black dashed line).



Tomarchio, L., Mosesso, L., Macis, S. et al. Electrodynamics of MnBi2Te4 intrinsic magnetic topological insulators. NPG Asia Mater 14, 82 (2022). DOI: https://doi.org/10.1038/s41427-022-00429-w 



Prof. Stefano Lupi
Department of Physics, Sapienza University, Piazzale Aldo Moro 5, 00185, Rome, Italy