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 $v_F=1.8cdot10^5$ m/s of massless Dirac fermions but also demonstrating significant non-linear dispersion at high energies.
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