Origin of beat patterns in the quantum magnetoresistance of gated InAs/GaSb and InAs/AlSb quantum wells

We present quantum magnetoresistance measurements on gated InAs/GaSb quantum wells over an extended range of temperature $(0.4<T<\mathrm{}31\mathrm{}\mathrm{K})$ and carrier concentration $(4.8\mathrm{}\times {10}^{11}{\mathrm{cm}}^{-2}<n<\mathrm{}3.6\mathrm{}\times {10}^{12}{\mathrm{cm}}^{\mathrm{-}2}).\mathrm{}$ At high enough carrier concentrations, a beating arising from a mixing of the first subband Shubnikov de–Haas (SdH) series and a magneto-intersubband (MIS) oscillation is observed, the onset of which occurs when the Fermi energy is close to the bottom of the second subband. It is only at the lowest concentrations where the well asymmetry is minimal that beat patterns due to two narrowly split SdH series are observed. This splitting energy is found to be dependent on magnetic field, dropping from ∼4.8 meV at $B=0\mathrm{}\mathrm{T}$ to ∼3.2 meV at $B=1.3\mathrm{}\mathrm{T}.$ In contrast, no beating is found in gated InAs/AlSb wells at 4.2 K until the Fermi energy enters the second subband, thereby allowing MIS scattering to occur.