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 semimetals (WSM) exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the crossing point of spin-polarized bands forming the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic WSM. We carried out angle-resolved photoelectron spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. The experiments reveal large spin- and orbital-angular-momentum (SAM and OAM) polarizations of the Weyl-fermion states, resulting from the broken crystalline inversion symmetry in TaAs. Supported by first-principles calculations, our measurements image signatures 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 provide directly bulk-sensitive spectroscopic support for the non-trivial band topology in the WSM TaAs, promising to have profound implications for the study of quantum-geometric effects in solids.
| Original language | English |
|---|---|
| Article number | 3650 |
| Journal | Nature Communications |
| Volume | 12 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2021 |
| Externally published | Yes |
Funding
This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through Project-ID 258499086-SFB 1170 (projects A01 and C07), the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter –ct.qmat Project-ID 390858490-EXC 2147, and RE1469/13-1. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III and we would like to thank Kai Bagschik, Jens Viefhaus, Frank Scholz, Jörn Seltmann, and Florian Trinter for assistance in using beamline P04. Funding for the photoemission spectroscopy instrument at beamline P04 (Contracts 05KS7FK2, 05K10FK1, 05K12FK1, and 05K13FK1 with Kiel University; 05KS7WW1 and 05K10WW2 with Würzburg University) by the Federal Ministry of Education and Research (BMBF) is gratefully acknowledged. The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 897276. We gratefully acknowledge the Gauss Centre for Supercomputing e.V. (www.gauss-centre.eu) for funding this project by providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Centre (www.lrz.de). J.N.N. and T.S. acknowledge support from the National Research Foundation, under Grant No. NSF DMR-1606952. The crystal synthesis and characterization was carried out at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation, Division of Materials Research under Grant No. DMR-1644779 and the state of Florida. This publication was supported by the Open Access Publication Fund of the University of Würzburg.
| Funders | Funder number |
|---|---|
| National Science Foundation | DMR-1606952 |
| Division of Materials Research | DMR-1644779 |
| Horizon 2020 Framework Programme | |
| H2020 Marie Skłodowska-Curie Actions | 897276 |
| National Research Foundation | |
| Deutsche Forschungsgemeinschaft | 05K10FK1, 258499086-SFB 1170, 390858490-EXC 2147, RE1469/13-1, 05K10WW2, 05KS7FK2, C07, 05K13FK1, 05K12FK1, 05KS7WW1 |
| Bundesministerium für Bildung und Forschung | |
| Julius-Maximilians-Universität Würzburg | |
| Leibniz-Rechenzentrum | |
| Gauss Centre for Supercomputing |