Breaking of the Usual Selection Rule for Magnetoluminescence in Doped Semiconductor Quantum Wells

We present experimental and theoretical evidence for impurity-assisted off-diagonal (i.e., $\Delta n>\mathrm{}0\mathrm{}$ transitions between conduction- and valence-band Landau levels ($n=0,1,\dots$) for magnetoluminescence in modulation-doped degenerate semiconductor quantum wells. This new selection rule is employed to determine simultaneously the optical effective masses of the electrons and in-plane light holes in $n$-type strained GaAs/InGaAs/AlGaAs quantum wells.