Measurements of Non-Local Resistances in the Quantum Anomalous Hall Regime

The quantum anomalous Hall effect (QAHE) is promising for revolutionizing the dissemination of quantum electrical standards. An improved understanding of the limitations of the QAHE are needed to implement such next generation standards. We report experimental results of conventional resistance and non-local measurements in the QAH regime of a Hall bar geometry device made from a high-quality 6 quintuple layer modulation-doped sample of the magnetic topological insulator, Cr-doped (BiSb)₂Te₃. At dilution refrigerator temperatures (≈10 mK) this sample is well-quantized to within a few ppm of h/e². We observe non-local resistances at temperatures above the well-quantized QAHE regime.  They are measured as a function of temperature from the QAHE regime to 100 K which is well above the Curie temperature. The behavior is also characterized as a function of gate bias and current amplitude. We will discuss possible interpretations for these striking results.