The infrared magnetooptics group at Laboratoire Pierre Aigrain and the ENS Physics Department along with collaborators from Johannes Kepler University of Linz in Austria and BESSY-II in Berlin, Germany have demonstrated manifestations of non-trivial topology in bulk 3D electron transport at high magnetic fields in Pb1-xSnxSe semiconductor alloys. They thereby challenge the long-held paradigm that 2D topological surface states are the only manifestation of non-trivial band topology.

In a recently published article, they have observed that a strong magnetic field can significantly impact the energy gap and electronic transport of topological materials. In relativistic terms, the energy gap is related to the mass of the electrons. The team showed that as the magnetic field increases, the electron mass becomes lighter, the carrier group velocity is thus enhanced and the resistance of the material drops This is only true in topological materials. In trivial materials, the field enhances the electron mass, and the resistance of the material increases with increasing magnetic field, as normally expected.

This work has been published in Physical Review Letters, and was highlighted by the editors among their suggestions for exceptional articles. Phys. Rev. Lett. 119 106602 (2017)

This achievement complements a previous realization of the team and their collaborators, where they showed that the topological index of a material can be measured by precisely quantifying the velocity of its Dirac fermions. Nature Partner Journals Quantum Materials 2 26 (2017)

The work is partly supported by the LabEx ENS-ICFP.