Guilin Sun
Ansys Employee
Lumerical's material fitting algorithm is best used for nature materials. You can modify all the parameters to improve it. Please refer this link for more information: Tips for improving the quality of optical material fits
and some videos
Materials - Material Explorer - Material Fitting
Material Properties - Material Explorer - Adjusting Material Fitting Parameters

It seems the measured data may contain large errors as the real part has a jump. In case you cannot get a fitting as expected, you may need to check the fitting error and see if it is acceptable. The real part does not change much. So you may pay more attention to the imaginary part.

PS: Since Lumerical products have a dedicated forum, please post here later Photonics ÔÇö Ansys Learning Forum