  Exploring new topological phenomena and functionalities induced by strong
electron correlation has been a central issue in modern condensed-matter
physics. One example is a topological insulator (TI) state and its
functionality driven by the Coulomb repulsion rather than a spin-orbit
coupling. Here, we report a "correlation-driven" TI state realized in an
organic zero-gap system $\alpha$-(BETS)$_2$I$_3$. The surface metallic state
that emerges at low temperatures exhibits characteristic transport properties
of a gapless Dirac semimetal, evidencing the presence of a topological surface
state in this compound. Moreover, we observe a topological phase switching
between the TI state and non-equilibrium Dirac semimetal state by a dc current,
which is a unique functionality of a correlation-driven TI state. Our findings
demonstrate that correlation-driven TIs are promising candidates not only for
practical electronic devices but also as a field for discovering new
topological phenomena and phases.
