If you want the refractive index of 2D MXene Ti3C2Tx with a thickness of 30 and 400 nm, .You can take a look at the paper with the title below.
You can extract the optical permittivity from the curve using any software and then change it to n and k. Some software, such as Comsol and Lumerical FDTD, has the feature of adding the permittivity directly, with no need to change it to n and k .You can import them directly to Comsol or Lumerical FDTD.
There is another publication for No2CTx with 87nm. You can extract the refractive index from the curve and import it directly to the software.
"Highly broadband absorber using plasmonic titanium carbide (MXene)"
Plasmonic Nb2CTx MXene-MAPbI3 Heterostructure for Self-Powered Visible-NIR Photodiodes"