  We use the tight-binding model to study the effect of transverse electric
field on the low-temperature electronic specific heat (Cv) for armchair and
zigzag boron nitride nanotubes (ABNNTs and ZBNNTs). For wide-band-gap BNNTs,
electric field could significantly modulate their energy dispersions and shift
many electronic states close to the Fermi energy. Under a critical electric
field (Fc) the density of states show special peak structures and the vanishing
specific heat at zero field jumps to a giant one. Cv, at Fc's, has a value
comparable to that of the phonon specific heat and reveals strongly non-linear
dependence on temperature. The critical field strength and the value of giant
specific heat are closely related to nanotube's geometry. In the presence of
Fc's, the extra longitudinal magnetic flux could enhance the value of Cv again
at low temperature for ZBNNTs, whereas it is not always true for ABNNTs.
