Two-dimensional type-II Dirac fermions in layered oxides.
basic_science · Level V
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- Record sourced from PubMed, PMID 30108225.
- Also identified by DOI 10.1038/s41467-018-05715-2 and PMC identifier 6092334.
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Abstract
Relativistic massless Dirac fermions can be probed with high-energy physics experiments, but appear also as low-energy quasi-particle excitations in electronic band structures. In condensed matter systems, their massless nature can be protected by crystal symmetries. Classification of such symmetry-protected relativistic band degeneracies has been fruitful, although many of the predicted quasi-particles still await their experimental discovery. Here we reveal, using angle-resolved photoemission spectroscopy, the existence of two-dimensional type-II Dirac fermions in the high-temperature superconductor La<sub>1.77</sub>Sr<sub>0.23</sub>CuO<sub>4</sub>. The Dirac point, constituting the crossing of [Formula: see text] and [Formula: see text] bands, is found approximately one electronvolt below the Fermi level (E<sub>F</sub>) and is protected by mirror symmetry. If spin-orbit coupling is considered, the Dirac point degeneracy is lifted and the bands acquire a topologically non-trivial character. In certain nickelate systems, band structure calculations suggest that the same type-II Dirac fermions can be realised near E<sub>F</sub>.