We report a direct observation of temperature-induced topological phasetransition between trivial and topological insulator in HgTe quantum well. Byusing a gated Hall bar device, we measure and represent Landau levels in fancharts at different temperatures and we follow the temperature evolution of apeculiar pair of "zero-mode" Landau levels, which split from the edge ofelectron-like and hole-like subbands. Their crossing at critical magnetic field$B_c$ is a characteristic of inverted band structure in the quantum well. Bymeasuring the temperature dependence of $B_c$, we directly extract the criticaltemperature $T_c$, at which the bulk band-gap vanishes and the topologicalphase transition occurs. Above this critical temperature, the opening of atrivial gap is clearly observed.
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