Anisotropic and strong negative magneto-resistance in the three-dimensional topological insulator Bi2Se3

Researchers at the HFML have investigated the magneto-resistance of epitaxial Bi2Se3 films, a three dimensional topological insulator, in a large temperature range, under tilt angle and in high magnetic fields. They found that the magneto-resistance exhibits a peculiar anisotropy depending on the orientation of the current (electric field) with respect to the applied magnetic field. Their observation of a negative longitudinal magneto-resistance in Bi2Se3 that is considered to be a fingerprint of topological semi-metals suggests being a universal phenomenon. The results have been published as a Rapid Communication in Physical Review B in August 2016 as an Editors’ Suggestion.

Magnetoresistance (MR) studies are one of the simplest yet powerful tools to investigate the electronic properties of solids. The researchers have performed angle-dependent magneto-transport measurements on epitaxial thin films of Bi2Se3, a three-dimensional topological insulator. At low temperature, they observe quantum oscillations that demonstrate the simultaneous presence of bulk and topologically protected surface states.

Fig. 1: (top) Measurement configurations - current with respect to the applied magnetic field. (middle) Anisotropic MR as a function of the applied magnetic field in configuration [i] and [ii] at room temperature. (bottom) Normalized resistivity as a function of the magnetic fields for both configurations at 4.2 K: the MR is superimposed by quantum oscillations. The NLMR is only observed if the magnetic field is applied parallel with respect to the current (configuration [ii]).

Their key observation is a strong anisotropy in the magnetoresistance in Bi2Se3 which depends on the orientation of the applied current (electric field) with respect to the applied magnetic field. In case the magnetic field is applied parallel to the electric field, they have observed a strong negative longitudinal magneto-resistance (NLMR) that, quite strikingly, persists even up to room temperature. With this finding, the researchers demonstrate that the observation of a NLMR is not unique to topological semi-metals such as Weyl semi-metals and therefore cannot by itself be taken as a diagnostic tool and as conclusive evidence for the existence of Weyl fermions where the NLMR is attributed to charge pumping between the Weyl points referred to as chiral (axial) anomaly.

These results could pave the way towards a general understanding of the emergence of the axial anomaly that is suggested to be a universal phenomenon for generic three-dimensional metals in the presence of parallel electric and magnetic fields.

Publication:

S. Wiedmann, A. Jost, B. Fauqué, J. van Dijk, M. J. Meijer, T. Khouri, S. Pezzini, S. Grauer, S. Schreyeck, C. Brüne, H. Buhmann, L. W. Molenkamp, and N. E. Hussey
Phys. Rev. B, 94 (2016)
DOI: http://dx.doi.org/10.1103/PhysRevB.94.081302

This publication is the product of collaboration between physicists from the University of Würzburg (EP3), the Ecole supérieure de physique et de chimie industrielles (ESPCI) in Paris and the High Field Magnet Laboratory (HFML) of the Radboud University and FOM Foundation.