The transconductance of an accumulation layer on $n$-type InAs is studied in a magnetic field $\overrightarrow{\mathrm{H}}$ parallel to the layer. Structures are observed, nonperiodic in $\frac{1}{H}$, corresponding to mixed electric and magnetic subbands. The effect promises a simple, sensitive method of probing the shape of the self-consistent potential in surface space-charge layers with multiply occupied subbands.

• Received 18 August 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.1593