Abstract
The energy spectrum of the conduction band in HgTe/Cd_xHg_1-xTe quantum wells of a width d=(4.6-20.2) nm has been experimentally studied in a wide range of electron density. For this purpose, the electron density dependence of the effective mass was measured by two methods: by analyzing the temperature dependence of the Shubnikov-de Haas oscillations and by means of the quantum capacitance measurements. There was shown that the effective mass obtained for the structures with d<d_c, where d_c≃6.3 nm is a critical width of quantum well corresponding to the Dirac-like energy spectrum, is close to the calculated values over the whole electron density range; with increasing width, at d>(7-8) nm, the experimental effective mass becomes noticeably less than the calculated ones. This difference increases with the electron density decrease, i.e., with lowering the Fermi energy; the maximal difference between the theory and experiment is achieved at d = (15-18) nm, where the ratio between the calculated and experimental masses reaches the value of two and begins to decrease with a further d increase. We assume that observed behavior of the electron effective mass results from the spectrum renormalization due to electron-electron interaction.