Observation of unconventional chiral fermions with long Fermi arcs in CoSi

Rao, Zhicheng; Li, Hang; Zhang, Tiantian; Tian, Shangjie; Li, Chenghe; Bao, Futing; Tang, Cenyao; Wang, Le; Li, Zhilin; Fan, Wenhui; Li, Jiajun; Huang, Yaobo; Liu, Zhehong; Long, Youwen; Fang, Chen; Weng, Hongming; Shi, Youguo; Lei, Hechang; Sun, Yujuan; Qian, Tian; Ding, Hong

doi:10.1038/s41586-019-1031-8

Cited by 330 publications

(271 citation statements)

References 31 publications

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“…1h shows a threefold-degenerate point at the Brillouin zone (BZ) centre It has been known that the surface projections of chiral fermions are surrounded by helical surface states [35]. The helical surface states for CoSi have been theoretically predicted [28,30] and experimentally confirmed on the (001) surface [31,33] It should be mentioned that the SOC effects exist in these materials. Due to the lack of inversion symmetry, the bands of both bulk and surface states split when SOC is included, as shown in our calculations with SOC in the Supplementary Figs.…”

Section: Introductionmentioning

confidence: 99%

“…Recent angle-resolved photoemission spectroscopy (ARPES) experiments have confirmed new types of degenerate points that carry nonzero chiral charges in a series of crystals CoSi, RhSi, and PtAl [31][32][33][34], providing a new platform for exploring the physical properties of chiral fermions. It is worth noting that all these materials belong to space group P213 (#198) with structural chirality, making it possible to study the connection between the chiral lattices in real space and the chiral fermions in momentum space [34].…”

Section: Introductionmentioning

confidence: 99%

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Chiral fermion reversal in chiral crystals

Li¹,

Xu²,

Rao³

et al. 2019

Nat Commun

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In materials chiral fermions such as Weyl fermions are characterized by nonzero chiral charges, which are singular points of Berry curvature in momentum space. Recently, new types of chiral fermions beyond Weyl fermions have been discovered in structurally chiral crystals CoSi, RhSi and PtAl. Here, we have synthesized RhSn single crystals, which have opposite structural chirality to the CoSi crystals we previously studied. Using angle-resolved photoemission spectroscopy, we show that the bulk electronic structures of RhSn are consistent with the band calculations and observe evident surface Fermi arcs and helical surface bands, confirming the existence of chiral fermions in RhSn. It is noteworthy that the helical surface bands of the RhSn and CoSi crystals have opposite handedness, meaning that the chiral fermions are reversed in the crystals of opposite structural chirality. Our discovery establishes a direct connection between chiral fermions in momentum space and chiral lattices in real space.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Chiral fermion reversal in chiral crystals

Li¹,

Xu²,

Rao³

et al. 2019

Nat Commun

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“…

to the emerging class of materials with non-trivial electronic band structure like topological insulators, Dirac or Weyl materials, featuring different topologically protected electronic states. Remarkably, recently long Fermi arcs were observed in the fermionic material CoSi by Rao et al [2] Also, Sanchez et al [3] discovered helicoid-arc quantum states in CoSi.A necessary condition for the existence of Weyl fermions is a broken space or time inversion symmetry. [1] These Weyl fermions carry a non-zero chiral charge and always appear in pairs.

…”

mentioning

confidence: 98%

Signatures of a Charge Density Wave Phase and the Chiral Anomaly in the Fermionic Material Cobalt Monosilicide CoSi

Schnatmann

Geishendorf

Lammel

et al. 2019

Adv Elect Materials

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to the emerging class of materials with non-trivial electronic band structure like topological insulators, Dirac or Weyl materials, featuring different topologically protected electronic states. In Weyl materials, these topologically protected electronic states are highly stable quasiparticles in the bulk, known as Weyl fermions, that were first predicted by Hermann Weyl in 1929. [1] These Weyl fermions carry a non-zero chiral charge and always appear in pairs. In a common Weyl material, this chiral charge is ±1; hence, the total chiral charge is zero. In contrast, the fermionic materials host Weyl fermions that are degenerated and carry a higher chiral charge. Remarkably, recently long Fermi arcs were observed in the fermionic material CoSi by Rao et al. [2] Also, Sanchez et al. [3] discovered helicoid-arc quantum states in CoSi.A necessary condition for the existence of Weyl fermions is a broken space or time inversion symmetry. The chiral charge of the material strongly depends on the space group of the crystal structure. CoSi has a cubic B20 crystal structure (space group 198 P2 1 3) with broken space inversion symmetry. This space group was predicted to host sixfold degenerated Weyl fermions. [4] In CoSi, the Weyl fermions carry a chiral charge of up to ±4. In detail, spin 1 excitations with a chiral charge of ±2 and spin 3/2 excitations with a chiral charge of ±4 (Rarita-Schwinger-Weyl fermions) were predicted. [5,6] Electrical transport experiments are a powerful tool to probe the energy spectrum of a material and thereby the specific nature of Weyl fermions. Topological states are massless due to the linear dispersion relation, and thus have an extremely high mobility. While often superimposed by the normal band transport, contributions of the Weyl fermions increase the total electrical conductivity. Consequently, the emerging class of materials with non-trivial electronic band structure has a large overlap with other classes of functional materials like the class of thermoelectric materials. [7] This also holds for CoSi. [5,8,9] Interestingly, related silicides like MnSi, [10] Fe 0.75 Co 0.25 Si [11] and germanides like Fe 1 −x Co x Ge [12,13] also feature skyrmion states.In general, Weyl materials show characteristic quantum effects in the transport, resulting for example in quantum Materials with topological electronic states have emerged as one of the most exciting discoveries of condensed quantum matter, hosting quasiparticles with extremely low effective mass and high mobility. Weyl materials contain such topological states in the bulk and additionally have a non-trivial chiral charge. However, despite known quantum effects caused by these chiral states, the interplay between chiral states, and a charge density wave phase, an ordering of the electrons to a correlated phase is not experimentally explored. Indications for the formation of a charge density wave phase in the Weyl material cobalt monosilicide CoSi are observed. Furthermore, the typical signatures of the charge density wave phase together...

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“…198), especially in compounds such as CoSi, RhSi, PtAl, CoGe, RhGe, PdGa etc. 1, [4][5][6][7]11 . Protected by this topological Chern number of ±4, there exist four Fermi arcs crossing surface-projected multifold fermions at high-symmetry points.…”

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confidence: 99%

Observation of giant spin-split Fermi-arc with maximal Chern number in the chiral topological semimetal PtGa

et al. 2020

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Non-symmorphic chiral topological crystals host exotic multifold fermions, and their associated Fermi arcs helically wrap around and expand throughout the Brillouin zone between the high-symmetry center (  ) and surface-corner ( M ) 1-7 momenta. However, Fermi-arc splitting and realization of the theoretically proposed maximal Chern number rely heavily on the spin-orbit coupling (SOC) strength. In the present work, we investigate the topological states of a new chiral crystal, PtGa, which has the strongest SOC among all chiral crystals reported to date. With a comprehensive investigation using high-resolution angleresolved photoemission spectroscopy, quantum-oscillation measurements, and state-of-theart ab initio calculations, we report a giant SOC-induced splitting of both Fermi arcs and bulk states. Consequently, this study experimentally confirms the realization of a maximal Chern number equal to ±4 for the first time in multifold fermionic systems, thereby providing a platform to observe large-quantized photogalvanic currents in optical experiments 2,8-11 .

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Observation of unconventional chiral fermions with long Fermi arcs in CoSi

Cited by 330 publications

References 31 publications

Chiral fermion reversal in chiral crystals

Chiral fermion reversal in chiral crystals

Signatures of a Charge Density Wave Phase and the Chiral Anomaly in the Fermionic Material Cobalt Monosilicide CoSi

Observation of giant spin-split Fermi-arc with maximal Chern number in the chiral topological semimetal PtGa

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