Magnetotransport evidence for the coexistence of trivial and topological phases in the band spectrum of bulk <i>n</i> -HgTe with extremely low electron density

Magnetotransport phenomena are investigated in a nominally pure n-HgTe single crystal with an exceptionally low electron concentration of 7.3 × 1014 cm−3. The results enable the proposal and validation of a band model positing the coexistence of two distinct electronic phases within the Brillouin zone: a trivial (intrinsic gapless) phase and a nontrivial (Weyl semimetal) phase. The trivial phase is identified by two principal signatures: a T32 power-law temperature dependence of the electron concentration and a strictly quadratic magnetic-field dependence of the transverse magnetoresistance at elevated temperatures. Conversely, the nontrivial phase is characterized by three key hallmarks: a large, non-saturating transverse magnetoresistance at low temperatures; the observation of the chiral magnetic effect as a direct consequence of the chiral anomaly; and an unconventional magnetic-field dependence of the Hall resistance at 0.3 K, which may be indicative of Weyl node annihilation in the quantum limit. Based on this second set of signatures, low-electron-density n-HgTe can be classified as a suitable candidate for a non-centrosymmetric Weyl semimetal. The obtained results are of significant interest both for fundamental condensed matter physics and for potential applications in spintronics, optoelectronics, and magnetic sensorics.