Magnetotransport measurements on a high-quality InAs/GaSb quantum well show single-period Shubnikov-de Haas (SdH) oscillations at low magnetic fields under dark conditions after initial sample cool down to 4.2 K. However, during and after illumination of the sample with infrared light, a beating pattern is observed in the SdH oscillations, indicating the possible appearance of two sets of Landau levels at low fields. Furthermore, for each condition, the original oscillation pattern persists under the application of a positive (or negative) backgate voltage that increases (or decreases) the two-dimensional electron gas density. © 2005 Elsevier B.V. All rights reserved.