Magnetic-Field-Induced Localization Transition in HgCdTe

We have performed magnetoresistance and Hall-resistance measurements on low-carrier-concentration $n$-type samples of ${\mathrm{Hg}}_{0.76}$${\mathrm{Cd}}_{0.24}$Te at millikelvin temperatures. We observe an abrupt rise in the Hall resistance and magnetoresistance at a characteristic field $H_c$ which is a significant function of temperature and which allows us to reject magnetic freezeout or localization by disorder as possible mechanisms. We believe our data provide compelling evidence for a model where the magnetic field induces localization of the electrons into a three-dimensional Wigner lattice.