A pressure-induced topological phase with large Berry curvature in Pb1−xSnxTe

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Science Advances  31 May 2017:
Vol. 3, no. 5, e1602510
DOI: 10.1126/sciadv.1602510

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The picture of how a gap closes in a semiconductor has been radically transformed by topological concepts. Instead of the gap closing and immediately reopening, topological arguments predict that, in the absence of inversion symmetry, a metallic phase protected by Weyl nodes persists over a finite interval of the tuning parameter (for example, pressure P). The gap reappears when the Weyl nodes mutually annihilate. We report evidence that Pb1−xSnxTe exhibits this topological metallic phase. Using pressure to tune the gap, we have tracked the nucleation of a Fermi surface droplet that rapidly grows in volume with P. In the metallic state, we observe a large Berry curvature, which dominates the Hall effect. Moreover, a giant negative magnetoresistance is observed in the insulating side of phase boundaries, in accord with ab initio calculations. The results confirm the existence of a topological metallic phase over a finite pressure interval.

  • Topological phases of matter
  • Berry curvature
  • anomalous Hall effect
  • PbSnTe
  • Gap tuning by pressure
  • Weyl fermions
  • giant magnetoresistance

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