  The interplay between electron correlation and topology of relativistic
electrons may lead to a new stage of the research on quantum materials and
emergent functions. The emergence of various collective electronic
orderings/liquids, which are tunable by external stimuli, is a remarkable
feature of correlated electron systems, but has rarely been realized in the
topological semimetals with high-mobility relativistic electrons. Here, we
report that the correlated Dirac electrons with the Mott criticality in
perovskite CaIrO$_3$ show unconventional field-induced successive
metal-insulator-metal crossovers in the quantum limit accompanying a giant
magnetoresistance (MR) with MR ratio of 3,500 % (18 T and 1.4 K). The analysis
shows that the insulating state originates from the collective electronic
ordering such as charge/spin density wave promoted by electron correlation,
whereas it turns into the quasi-one-dimensional metal at higher fields due to
the field-induced reduction of chemical potential, highlighting the highly
field-sensitive character of correlated Dirac electrons.
