Magnetoconductance evolution across the topological-trivial phase transition in ${In_{x}}({Bi_{0.3}}{Sb_{0.7}})_{2-x}{Te_3}$ thin films

We investigate the evolution of electronic transport across the topological-trivial phase transition in ${\rm In}{x}({\rm Bi}{0.3}{\rm Sb}{0.7}){2-x}{\rm Te}_3$ thin films by systematically tuning the indium concentration $x$. Increasing $x$ reduces the effective spin-orbit coupling, driving a topological quantum phase transition near $x \approx 7%$, and at higher disorder a crossover from diffusive to strongly localized transport around $x \approx 15%$. In the diffusive regime, the magnetoconductance is well described by the Hikami-Larkin-Nagaoka formalism, with the evolution of the WAL prefactor $α$ correlating with the band-inversion transition. Beyond the diffusive limit, transport crosses into variable-range hopping, accompanied by a striking reversal of magnetoconductance from negative to positive. The observed positive low-field magnetoconductance, its pronounced anisotropy, and its temperature evolution point to an orbital origin of the response. These features are naturally captured by incorporating the incoherent hopping mechanism of Raikh \textit{et al.} together with wavefunction shrinkage, rather than by conventional quantum-correction frameworks. Our results provide a unified picture of how topology, spin-orbit coupling, and disorder collectively determine the full field-temperature magnetotransport landscape in this material class, establishing a clear experimental link between the topological phase transition and the onset of incoherent hopping-dominated conduction.

💡 Research Summary

In this work the authors systematically explore how electronic transport evolves across a topological‑trivial quantum phase transition and a disorder‑driven localization transition in Inₓ(Bi₀.₃Sb₀.₇)₂₋ₓTe₃ thin films. By varying the indium concentration x from 0 % to 25 % they tune the effective spin‑orbit coupling: increasing x weakens the spin‑orbit interaction, closes the inverted bulk gap, and re‑opens it with normal ordering near x ≈ 7 %, marking a topological quantum phase transition (TQPT).

Structural characterization by X‑ray diffraction confirms highly c‑axis‑oriented 100 nm films grown by pulsed laser deposition. Electrical transport measurements from 2 K to 300 K reveal three distinct regimes. For x < 7 % the resistance decreases at low temperature, indicating metallic surface transport typical of a topological insulator. Magnetoconductance (MC) is negative and well described by the Hikami‑Larkin‑Nagaoka (HLN) formula, Δσ = −α(e²/2π²ħ)