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A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class.

Huang SM, Xu SY, Belopolski I, Lee CC, Chang G, Wang B, Alidoust N, Bian G, Neupane M, Zhang C, Jia S, Bansil A, Lin H, Hasan MZ - Nat Commun (2015)

Bottom Line: Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators.Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class.Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

View Article: PubMed Central - PubMed

Affiliation: 1] Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore [2] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.

ABSTRACT
Weyl fermions are massless chiral fermions that play an important role in quantum field theory but have never been observed as fundamental particles. A Weyl semimetal is an unusual crystal that hosts Weyl fermions as quasiparticle excitations and features Fermi arcs on its surface. Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators. Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class. Our first-principles calculations on TaAs reveal its bulk Weyl fermion cones and surface Fermi arcs. Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

No MeSH data available.


Related in: MedlinePlus

The electronic structure of the Weyl semimetal TaAs.(a) The bulk electronic structure of TaAs in the absence of spin–orbit coupling from DFT. (b) The band structure in the vicinity of the Fermi level along the Σ−N−Σ1 direction. (c,d) The same as panels a and b but in the presence of spin–orbit coupling.
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f2: The electronic structure of the Weyl semimetal TaAs.(a) The bulk electronic structure of TaAs in the absence of spin–orbit coupling from DFT. (b) The band structure in the vicinity of the Fermi level along the Σ−N−Σ1 direction. (c,d) The same as panels a and b but in the presence of spin–orbit coupling.

Mentions: The ionic model would suggest that the Ta and As atoms are in the 3+ and 3− valence states, respectively. This indicates that the lowest valence band arises from 4p6 electrons in As and 5d2 electrons in Ta, whereas the lowest conduction band primarily consists of 5d electrons in Ta. However, we may expect Ta 5d electrons to have a broad bandwidth because of the wide extent of the atomic orbitals. This leads to strong hybridization with the As 4p states, which may suggest that the conduction and valence bands are not entirely separated in energy and have a small overlap, giving rise to a semimetal. In Fig. 2a, we present the bulk band structure in the absence of spin–orbit coupling. The conduction and valence bands cross each other along the Σ–N–Σ1 trajectory, which further indicates that TaAs is a semimetal. In the presence of spin–orbit coupling, the band structure is fully gapped along the high-symmetry directions considered in Fig. 2c. However, Weyl points which are shifted away from the high-symmetry lines arise after spin–orbit coupling is taken into account. Below, we consider the Weyl points in the bulk BZ. We also note that the double degeneracy of bands is lifted in the presence of spin–orbit coupling except at the Kramers' points, which confirms that TaAs breaks inversion symmetry but respects time-reversal symmetry.


A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class.

Huang SM, Xu SY, Belopolski I, Lee CC, Chang G, Wang B, Alidoust N, Bian G, Neupane M, Zhang C, Jia S, Bansil A, Lin H, Hasan MZ - Nat Commun (2015)

The electronic structure of the Weyl semimetal TaAs.(a) The bulk electronic structure of TaAs in the absence of spin–orbit coupling from DFT. (b) The band structure in the vicinity of the Fermi level along the Σ−N−Σ1 direction. (c,d) The same as panels a and b but in the presence of spin–orbit coupling.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490374&req=5

f2: The electronic structure of the Weyl semimetal TaAs.(a) The bulk electronic structure of TaAs in the absence of spin–orbit coupling from DFT. (b) The band structure in the vicinity of the Fermi level along the Σ−N−Σ1 direction. (c,d) The same as panels a and b but in the presence of spin–orbit coupling.
Mentions: The ionic model would suggest that the Ta and As atoms are in the 3+ and 3− valence states, respectively. This indicates that the lowest valence band arises from 4p6 electrons in As and 5d2 electrons in Ta, whereas the lowest conduction band primarily consists of 5d electrons in Ta. However, we may expect Ta 5d electrons to have a broad bandwidth because of the wide extent of the atomic orbitals. This leads to strong hybridization with the As 4p states, which may suggest that the conduction and valence bands are not entirely separated in energy and have a small overlap, giving rise to a semimetal. In Fig. 2a, we present the bulk band structure in the absence of spin–orbit coupling. The conduction and valence bands cross each other along the Σ–N–Σ1 trajectory, which further indicates that TaAs is a semimetal. In the presence of spin–orbit coupling, the band structure is fully gapped along the high-symmetry directions considered in Fig. 2c. However, Weyl points which are shifted away from the high-symmetry lines arise after spin–orbit coupling is taken into account. Below, we consider the Weyl points in the bulk BZ. We also note that the double degeneracy of bands is lifted in the presence of spin–orbit coupling except at the Kramers' points, which confirms that TaAs breaks inversion symmetry but respects time-reversal symmetry.

Bottom Line: Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators.Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class.Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

View Article: PubMed Central - PubMed

Affiliation: 1] Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore [2] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.

ABSTRACT
Weyl fermions are massless chiral fermions that play an important role in quantum field theory but have never been observed as fundamental particles. A Weyl semimetal is an unusual crystal that hosts Weyl fermions as quasiparticle excitations and features Fermi arcs on its surface. Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators. Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class. Our first-principles calculations on TaAs reveal its bulk Weyl fermion cones and surface Fermi arcs. Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

No MeSH data available.


Related in: MedlinePlus