  Quantum materials (QMs) with strong correlation and non-trivial topology are
indispensable to next-generation information and computing technologies.
Exploitation of topological band structure is an ideal starting point to
realize correlated topological QMs. Herein, we report that strain-induced
symmetry modification in correlated oxide SrNbO3 thin films creates an emerging
topological band structure. Dirac electrons in strained SrNbO3 films reveal
ultra-high mobility (100,000 cm2/Vs), exceptionally small effective mass
(0.04me), and non-zero Berry phase. More importantly, strained SrNbO3 films
reach the extreme quantum limit, exhibiting a sign of fractional occupation of
Landau levels and giant mass enhancement. Our results suggest that
symmetry-modified SrNbO3 is a rare example of a correlated topological QM, in
which strong correlation of Dirac electrons leads to the realization of
fractional occupation of Landau levels.
