  The Landau level laser has been proposed a long time ago as a unique source
of monochromatic radiation, widely tunable in the THz and infrared spectral
ranges using an externally applied magnetic field. In spite of decades of
efforts, this appealing concept never resulted in the design of a reliable
device. This is due to efficient Auger scattering of Landau-quantized
electrons, which is an intrinsic non-radiative recombination channel that
eventually gains over cyclotron emission in all materials studied so far: in
conventional semiconductors with parabolic bands, but also in graphene with
massless electrons. The Auger processes are favored in these systems by Landau
levels (or their subsets) equally spaced in energy. Here we show that this
scheme does not apply to massless Kane electrons in gapless HgCdTe alloy, in
which undesirable Auger scattering is strongly suppressed and the sizeable
cyclotron emission observed, for the first time in the case of massless
particles. The gapless HgCdTe thus appears as a material of choice for future
technology of Landau level lasers.
