Transport signatures of Fermi surface topology change in BiTeI

We report a quantum magnetotransport signature of a change in the Fermi surface topology in the Rashba semiconductor BiTeI with a systematic tuning of the Fermi level E-F. Beyond the quantum limit, we observe a marked increase (decrease) in electrical resistivity when E-F is above (below) the Dirac node that we show originates from the Fermi surface topology. This effect represents a measurement of the electron distribution on low-index (n = 0,-1) Landau levels and is uniquely enabled by the finite bulk k(z) dispersion along the c axis and strong Rashba spin-orbit coupling strength of the system. The Dirac node is independently identified by Shubnikov-de Haas oscillations as a vanishing Fermi surface cross section at k(z) = 0. Additionally, we find that the violation of Kohler's rule allows a distinct insight into the temperature evolution of the observed quantum magnetoresistance effects.