The energy spectrum of the conduction band in HgTe/CdxβHg1βxβTe quantum
wells of a width d=(4.6β20.2) 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<dcβ, where dcββ6.3 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>(7β8) 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=(15β18) 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.Comment: 8 pages, 10 figure