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 $\left(n=0,-1\right)$ 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.

Figure 1

(a) Location of the Fermi surface (FS) in the Brillouin zone. Magnetic field $B$ is applied along the $c$ axis (parallel to the $z$ direction). (b) Schematic evolution of the three-dimensional FS (compressed in the $k_z$ direction for clarity) of BiTeI from a spindle torus $\left(E_F>0\right)$ through a horn torus $\left(E_F=0\right)$ to a ring torus $\left(E_F<0\right)$. Dashed lines define the IFS. (c) Representative $\rho \left(T\right)$ of samples with $E_F$ above (green), near (black), and below (blue) the Dirac point, with the Hall carrier density denoted in parentheses.

Figure 2

(a) Normalized MR of samples A–H. Curves are scaled and offset to emphasize Landau-level-related patterns. Triangles denote the IFS quantum limit and the dashed lines are extrapolations of the MR below the quantum limit. (b) Simulated IFS density of states $D^{\text{IFS}}$ for samples A–H. Curves are normalized and offset for clarity. (c) $E_F$ of samples A–H relative to the Dirac point. (d) In-plane dispersion at $k_z=0$ when $B=0$ (upper axis) and selected Landau levels as a function of $B$ (lower axis). The colors blue and green represent respectively the IFS and OFS Landau levels. (e) Magnified $B$ evolution of $D^{\text{IFS}}$ near the Dirac point.

Figure 3

(a) OFS and IFS radii at $k_z=0$ $(k_{\text{OFS}}$ and $k_{\text{IFS}})$ for all measured samples with line fits for $E_F>0$ and $E_F<0$, respectively. The Rashba bands are shown in the inset. (b) IFS index plot of samples A, B, C, D, G, and H. The inset shows the oscillatory resistivity after background subtraction.

Figure 4

(a)–(d) Temperature evolution of MR captured by the Kohler's plot of samples A, C, F, and G; black triangles denote the quantum limit for $T=10$ K. The inset of (d) shows the positions of $E_F$ at 14 T for each sample.