High-Temperature Quantum Hall Effect In Finite Gapped Hgte Quantum Wells

We report on the observation of the quantum Hall effect at high temperatures in HgTe quantum wells with a finite band gap and a thickness below and above the critical thickness d(c) that separates a conventional semiconductor from a two-dimensional topological insulator. At high carrier concentrations, we observe a quantized Hall conductivity up to 60 K with energy gaps between Landau levels of the order of 25 meV, in good agreement with the Landau level spectrum obtained from k . p calculations. Using the scaling approach for the plateau-plateau transition at nu = 2 -> 1, we find the scaling coefficient kappa = 0.45 +/- 0.04 to be consistent with the universality of scaling theory, and we do not find signs of increased electron-phonon interaction to alter the scaling even at these elevated temperatures. Comparing the high-temperature limit of the quantized Hall resistance in HgTe quantum wells with a finite band gap with room-temperature experiment in graphene, we find that the energy gaps at the breakdown of the quantization exceed the thermal energy by the same order of magnitude.