Second subband population of the two-dimensional electron gas in strongly coupled $\mathrm{GaAs}/{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ double quantum wells

The two-dimensional electron system in strongly coupled ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ double quantum wells has been studied by Shubnikov–de Haas (SdH) measurements. The degenerate subbands of the double quantum wells are lifted into two subbands with a symmetric or antisymmetric wave function. We observed SdH oscillations due to the second subband of the antisymmetric wave function. The effective mass of the second subband increases with the magnetic field for a field range from 0.686 to 1.776 T. The magnetic-field-induced mass enhancement for double quantum wells with an equal well thickness is greater than that for those with an unequal one. This mass enhancement is attributed to the many-body effects of electron-electron interaction.