Physical Review Letters ( IF 8.385 ) Pub Date :
Y. K. Song, G. W. Wang, S. C. Li, W. L. Liu, X. L. Lu, Z. T. Liu, Z. J. Li, J. S. Wen, Z. P. Yin, Z. H. Liu, and D. W. Shen

Topological nodal-line semimetals with exotic quantum properties are characterized by symmetry-protected line-contact bulk band-crossings in the momentum space. However, in most of identified topological nodal-line compounds, these topological non-trivial nodal lines are enclosed by complicated topological trivial states at the Fermi energy (${E}_{F}$), which would perplex their identification and hinder further applications. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, we provide compelling evidence for the existence of Dirac nodal-line fermions in the monoclinic semimetal SrAs${}_{3}$, which possesses a simple nodal loop in the vicinity of ${E}_{F}$ without the distraction from complicated trivial Fermi surfaces. Our calculations revealed that two bands with opposite parities were inverted around near ${E}_{F}$, resulting in the single nodal loop at the $\Gamma$-- plane with a negligible spin-orbit coupling effect. The band crossings were tracked experimentally and the complete nodal loop was identified quantitatively, which provide a critical experimental support for the existence of nodal-line fermions in the CaP${}_{3}$ family of materials. Hosting simple topological non-trivial bulk electronic states around ${E}_{F}$ and without complication from the trivial states, SrAs${}_{3}$ is expected to be a potential platform for topological quantum state investigation and applications.

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