  Magnetic oscillations of Dirac surface states of topological insulators are
expected to be associated with the formation of Landau levels or the
Aharonov-Bohm effect. We instead study the conductance of Dirac surface states
subjected to an in-plane magnetic field in presence of a barrier potential.
Strikingly, we find that, in the case of large barrier potentials, the surface
states exhibit pronounced oscillations in the conductance when varying the
magnetic field, in the \textit{absence} of Landau levels or the Aharonov-Bohm
effect. These novel magnetic oscillations are attributed to the emergence of
\textit{super-resonant regimes} by tuning the magnetic field, in which almost
all propagating electrons cross the barrier with perfect transmission. In the
case of small and moderate barrier potentials, we also identify a positive
magnetoconductance which is due to the increase of the Fermi surface by tilting
the surface Dirac cone. Moreover, we show that for weak magnetic fields, the
conductance displays a shifted sinusoidal dependence on the field direction
with period $\pi$ and phase shift determined by the tilting direction with
respect to the field direction. Our predictions can be applied to many
topological insulators, such as HgTe and Bi$_{2}$Se$_{3}$, and provide
important insights into exploring and understanding exotic magnetotransport
properties of topological surface states.
