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Nat Mater. 2016 Nov;15(11):1155-1160. doi: 10.1038/nmat4685. Epub 2016 Jul 11.

Spectroscopic evidence for a type II Weyl semimetallic state in MoTe2.

Author information

1
Ames Laboratory, US DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
2
Department of Physics and Center for Emergent Materials, The Ohio State University, Columbus, Ohio 43210, USA.
3
Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan.
4
Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
5
RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.
6
JST ERATO Isobe Degenerate π-Integration Project, Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Miyagi 980-8577, Japan.
7
Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
8
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
9
Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.

Abstract

In a type I Dirac or Weyl semimetal, the low-energy states are squeezed to a single point in momentum space when the chemical potential μ is tuned precisely to the Dirac/Weyl point. Recently, a type II Weyl semimetal was predicted to exist, where the Weyl states connect hole and electron bands, separated by an indirect gap. This leads to unusual energy states, where hole and electron pockets touch at the Weyl point. Here we present the discovery of a type II topological Weyl semimetal state in pure MoTe2, where two sets of Weyl points (, ) exist at the touching points of electron and hole pockets and are located at different binding energies above EF. Using angle-resolved photoemission spectroscopy, modelling, density functional theory and calculations of Berry curvature, we identify the Weyl points and demonstrate that they are connected by different sets of Fermi arcs for each of the two surface terminations. We also find new surface 'track states' that form closed loops and are unique to type II Weyl semimetals. This material provides an exciting, new platform to study the properties of Weyl fermions.

PMID:
27400386
DOI:
10.1038/nmat4685

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