  We report the electrical transport properties for Weyl semimetal TaAs in an
intense magnetic field. Series of anomalies occur in the longitudinal
magnetoresistance and Hall signals at ultra-low temperatures when the Weyl
electrons are confined into the lowest Landau level. These strongly
temperature-dependent anomalies are ascribed to the electron-hole pairing
instability. Our measurements show that the Weyl semimetal TaAs in the
ultraquantum regime provides a good platform for studying electron-electron
interaction in topological nontrivial semimetals.
