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arXiv · 2012.06996

Momentum-space signatures of Berry flux monopoles in a Weyl semimetal

M. Ünzelmann·H. Bentmann·T. Figgemeier·P. Eck·J. N. Neu·B. Geldiyev·F. Diekmann·S. Rohlf·J. Buck·M. Hoesch·M. Kalläne·K. Rossnagel·R. Thomale·T. Siegrist·G. Sangiovanni·D. Di Sante·F. Reinert
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Abstract

Since the early days of Dirac flux quantization, magnetic monopoles have been sought after as a potential corollary of quantized electric charge. As opposed to magnetic monopoles embedded into the theory of electromagnetism, Weyl crystals exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the degeneracy point of the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic Weyl semimetal. We have probed the orbital and spin angular momentum (OAM and SAM) of the Weyl-fermion states by angle-resolved photoemission spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. Supported by first-principles calculations, our measurements image characteristics of a topologically non-trivial winding of the OAM at the Weyl nodes and unveil a chirality-dependent SAM of the Weyl bands. Our results experimentally visualize the non-trivial momentum-space topology in a Weyl semimetal, promising to have profound implications for the study of quantum-geometric effects in solids.

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M. Ünzelmann, H. Bentmann, T. Figgemeier, P. Eck, J. N. Neu, B. Geldiyev, F. Diekmann, S. Rohlf, J. Buck, M. Hoesch, M. Kalläne, K. Rossnagel, R. Thomale, T. Siegrist, G. Sangiovanni, D. Di Sante, F. Reinert. 2020-12-13. Momentum-space signatures of Berry flux monopoles in a Weyl semimetal. https://doi.org/10.1038/s41467-021-23727-3

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