  Bars drive gas inflow. As the gas flows inwards, shocks and shear occur along
the bar dust lanes. Such shocks and shear can affect the star formation and
change the gas properties. For four barred galaxies, we present H{\alpha}
velocity gradient maps that highlight bar-driven shocks and shear using data
from the PHANGS-MUSE and PHANGS-ALMA surveys which allow us to study bar
kinematics in unprecedented detail. Velocity gradients are enhanced along the
bar dust lanes, where shocks and shear are shown to occur in numerical
simulations. Velocity gradient maps also efficiently pick up expanding shells
around HII regions. We put pseudo slits on the regions where velocity gradients
are enhanced and find that H{\alpha} and CO velocities jump up to ~170 km/s,
even after removing the effects of circular motions due to the galaxy rotation.
Enhanced velocity gradients either coincide with the peak of CO intensity along
the bar dust lanes or are slightly offset from CO intensity peaks, depending on
the objects. Using the BPT diagnostic, we identify the source of ionization on
each spaxel and find that star formation is inhibited in the high velocity
gradient regions of the bar, and the majority of those regions are classified
as LINER or composite. This implies that star formation is inhibited where
bar-driven shear and shocks are strong. Our results are consistent with the
results from the numerical simulations that show star formation is inhibited in
the bar where shear force is strong.
