Magnetotransport spectroscopy of the interface, quantum well, and hybrid states in structures with 16-nm-thick multiple HgTe layers

The longitudinal and Hall components of the resistivity tensor are measured in structures with multiple HgTe layers 16 nm thick in magnetic fields to 12 T at temperatures from 1.5 to 300 K. The slope of the magnetic-field dependence of the Hall resistance is found to change its sign at a certain critical temperature $T_c$ = 5 and 10 K in the two studied samples, which indicates the presence of two types of charge carriers and a change in the relation between their contributions to the Hall resistance with temperature. The low critical temperature and manifestation of the “two-component” nature of the Hall curves only at $T>T_c$ prove that the ground state of the system at $T = T_c$ is gapless. At higher temperatures (20 K $< T <$ 200 K), the Hall concentration is proportional to the temperature with good accuracy. The description of the charge-carrier dispersion laws by the 8-band $\mathbf{kp}$ model taking into account $\Gamma_8$-band-edge splitting caused by mechanical stresses, which forms both types of state in HgTe, makes it possible to quantitatively describe the observed magnetotransport features. It is shown that they are associated with the simultaneous filling of electron and hole states formed as a result of mixing interface states responsible for the topological-insulator phase and the quantum-confined states in the $\Gamma_8$ band.