  We report on the clear evidence of massless Dirac fermions in two-dimensional
system based on III-V semiconductors. Using a gated Hall bar made on a
three-layer InAs/GaSb/InAs quantum well, we restore the Landau levels fan chart
by magnetotransport and unequivocally demonstrate a gapless state in our
sample. Measurements of cyclotron resonance at different electron
concentrations directly indicate a linear band crossing at the $\Gamma$ point
of Brillouin zone. Analysis of experimental data within analytical Dirac-like
Hamiltonian allows us not only determing velocity $v_F=1.8\cdot10^5$ m/s of
massless Dirac fermions but also demonstrating significant non-linear
dispersion at high energies.
