Figure 1: Preparation of (Cu_0.1Bi_0.9)₂Te_3.06 samples and their transport.

(a) The temperature evolution during preparation of the crystals. An ageing process is then followed to prepare the low-mobility samples. Our samples are mechanically exfoliated; their typical size is shown in the inset at the top right. The bottom-left inset also shows the X-ray powder diffraction measurement, confirming the crystalline ordering of Bi₂Te₃. (b) The MC curves of the samples at 2 K. Sample 1 is the sample without ageing, Samples 3 and 4 are aged for 600 days, whereas Sample 2 is with a larger mobility and a smaller ageing period. The MC curves for Samples 1 and 2 are plotted on the right axis, and those for Samples 3 and 4 are plotted on the left axis. (c) The temperature-dependent resistivity of our samples. (d) The temperature-dependent mobility of the four samples. The intensely aged flakes, that is, Samples 3 and 4, have super low-mobility values. The sample parameters can be found in Table 1.