  Solitons in nematic liquid crystals offer intriguing opportunities for
transport and sensing in microfluidic systems. Little is known about the
elementary conditions that are needed to create solitons in nematic materials.
In this work, theory, simulations and experiments are used to study the
generation and propagation of solitary waves (or "solitons") in nematic liquid
crystals upon the application of an alternating current (AC) electric field. We
find that these solitary waves exhibit "butterfly"-like or "bullet"-like
structures that travel in the direction perpendicular to the applied electric
field. Such structures propagate over long distances without losing their
initial shape. The theoretical model adopted here serves to identify some of
the key requirements that are needed to generate solitons in the absence of
electrostatic interactions. These include surface imperfections that introduce
a twist in the director, unequal elastic constants, and negative anisotropic
dielectric permittivity. The results of simulations are shown to be in good
agreement with our own experimental observations, serving to establish the
validity of the theoretical concepts advanced in this work.
