  Materials with linear electronic dispersion often feature high carrier
mobilities and unusually strong nonlinear optical interactions. In this work,
we investigate the THz nonlinear dynamics of one such material, HgCdTe, with an
electronic band dispersion heavily dependent on both temperature and
stoichiometry. We show how the band gap, carrier concentration and band shape
together determine the nonlinear response of the system. At low temperatures,
carrier generation from Zener tunneling dominates the nonlinear response with a
reduction in the overall transmission. At room temperature, quasi-ballistic
electronic dynamics drive the largest observed nonlinear optical interactions,
leading to a transmission increase. Our results demonstrate the sensitivity of
these nonlinear optical properties of narrow-gap materials to small changes in
the electronic dispersion and carrier concentration.
