CST: Eigenmode solver error

Hello, all,

I'm trying to plot dispersion diagram with CST. I need to use eigenmode solver, but there is always on error: Eigenmode solver does not support lossy metal materials. The lossy metal materials will be treated as PEC.

Here the lossy material is graphene. Trying to fix this, I changed the imaginary part of permittivity of my material to 0. I think now it should be lossless, but the erro still occurs. Anyone could help? Thanks in advance.

for substrate material choose (LOSS FREE)

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