Unconventional Large Linear Magnetoresistance in Cu$_{2-x}$Te

We report a large linear magnetoresistance in Cu$_{2-x}$Te, reaching $\Delta\rho/\rho(0)$ = 250\% at 2 K in a 9 T field. This is observed for samples with $x$ in the range 0.13 to 0.22, and the results are comparable to the effects observed in Ag$_2 X$ materials, although in this case the results appear for a much wider range of bulk carrier density. Examining the magnitude vs. crossover field from low-field quadratic to high-field linear behavior, we show that models based on classical transport behavior best explain the observed results. The effects are traced to misdirected currents due to topologically inverted behavior in this system, such that stable surface states provide the high mobility transport channels. The resistivity also crosses over to a $T^2$ dependence in the temperature range where the large linear MR appears, an indicator of electron-electron interaction effects within the surface states. Thus this is an example of a system in which these interactions dominate the low-temperature behavior of the surface states.