  We investigate the phase behavior of colloidal suspensions of board-like
particles under the effect of an external field and assess the still disputed
occurrence of the biaxial nematic (N$_\text{B}$) liquid crystal phase. The
external field promotes the rearrangement of the initial isotropic (I) or
uniaxial nematic (N$_\text{U}$) phase and the formation of the N$_\text{B}$
phase. In particular, very weak field strengths are sufficient to spark a
direct I-N$_\text{B}$ or N$_\text{U}$-N$_\text{B}$ phase transition at the
self-dual shape, where prolate and oblate particle geometries fuse into one. By
contrast, forming the N$_\text{B}$ phase at any other geometry requires
stronger fields and thus reduces the energy efficiency of the phase
transformation. Our simulation results show that self-dual shaped board-like
particles with moderate anisotropy are able to form N$_\text{B}$ liquid
crystals under the effect of a surprisingly weak external stimulus and suggest
a path to exploit low-energy uniaxial-to-biaxial order switching.
