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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

Crystal structure and Brillouin zone of the Weyl semimetal TaAs.(a) Body-centred tetragonal structure of TaAs, shown as stacked TaAs layers. An electric polarization is induced due to dimples in the TaAs lattice. (b) Shows top–down views at different vertical positions, emphasizing the fact that the crystal structure is composed of square lattices that are shifted with respect to one another. The arrangement of Ta atoms for each layer (Ta1 to Ta4) is illustrated in (c). (d) High symmetry points are noted as green and red dots in the bulk and the (001) surface Brillouin zones (BZ), respectively.
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f1: Crystal structure and Brillouin zone of the Weyl semimetal TaAs.(a) Body-centred tetragonal structure of TaAs, shown as stacked TaAs layers. An electric polarization is induced due to dimples in the TaAs lattice. (b) Shows top–down views at different vertical positions, emphasizing the fact that the crystal structure is composed of square lattices that are shifted with respect to one another. The arrangement of Ta atoms for each layer (Ta1 to Ta4) is illustrated in (c). (d) High symmetry points are noted as green and red dots in the bulk and the (001) surface Brillouin zones (BZ), respectively.

Mentions: In order to find a Weyl semimetal that respects time-reversal symmetry, one needs to search for materials that break space inversion symmetry. In addition, since the Weyl nodes in a Weyl semimetal are usually not located along any high-symmetry direction, one has to calculate the band structure throughout the bulk Brillouin zone (BZ) in order to check whether there are Weyl nodes in a material or not. We have therefore searched through hundreds of inversion symmetry-breaking materials, identified the ones that are likely to be semimetal or narrow bandgap semiconductors, and then performed systematic calculations of the bulk band structures to theoretically understand the nature of their electronic and topological groundstate. Tantalum arsenide crystalizes in a body-centered tetragonal lattice system (Fig. 1a–c). The lattice constants are a=3.437 Å and c=11.656 Å, and the space group is I41md (#109, C4v). This crystal consists of interpenetrating Ta and As sub-lattices, where the two sub-lattices are shifted by , . There are two Ta atoms and two As atoms in each primitive unit cell. It is important to note that the system lacks a horizontal mirror plane and thus inversion symmetry. This makes it possible to realize an inversion breaking Weyl semimetal in TaAs. We also note that the C4 rotational symmetry is broken at the (001) surface because the system is only invariant under a four-fold rotation with a translation along the out-of-plane direction. The bulk and (001) surface BZs are shown in Fig. 1d, where high-symmetry points are also noted.


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)

Crystal structure and Brillouin zone of the Weyl semimetal TaAs.(a) Body-centred tetragonal structure of TaAs, shown as stacked TaAs layers. An electric polarization is induced due to dimples in the TaAs lattice. (b) Shows top–down views at different vertical positions, emphasizing the fact that the crystal structure is composed of square lattices that are shifted with respect to one another. The arrangement of Ta atoms for each layer (Ta1 to Ta4) is illustrated in (c). (d) High symmetry points are noted as green and red dots in the bulk and the (001) surface Brillouin zones (BZ), respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Crystal structure and Brillouin zone of the Weyl semimetal TaAs.(a) Body-centred tetragonal structure of TaAs, shown as stacked TaAs layers. An electric polarization is induced due to dimples in the TaAs lattice. (b) Shows top–down views at different vertical positions, emphasizing the fact that the crystal structure is composed of square lattices that are shifted with respect to one another. The arrangement of Ta atoms for each layer (Ta1 to Ta4) is illustrated in (c). (d) High symmetry points are noted as green and red dots in the bulk and the (001) surface Brillouin zones (BZ), respectively.
Mentions: In order to find a Weyl semimetal that respects time-reversal symmetry, one needs to search for materials that break space inversion symmetry. In addition, since the Weyl nodes in a Weyl semimetal are usually not located along any high-symmetry direction, one has to calculate the band structure throughout the bulk Brillouin zone (BZ) in order to check whether there are Weyl nodes in a material or not. We have therefore searched through hundreds of inversion symmetry-breaking materials, identified the ones that are likely to be semimetal or narrow bandgap semiconductors, and then performed systematic calculations of the bulk band structures to theoretically understand the nature of their electronic and topological groundstate. Tantalum arsenide crystalizes in a body-centered tetragonal lattice system (Fig. 1a–c). The lattice constants are a=3.437 Å and c=11.656 Å, and the space group is I41md (#109, C4v). This crystal consists of interpenetrating Ta and As sub-lattices, where the two sub-lattices are shifted by , . There are two Ta atoms and two As atoms in each primitive unit cell. It is important to note that the system lacks a horizontal mirror plane and thus inversion symmetry. This makes it possible to realize an inversion breaking Weyl semimetal in TaAs. We also note that the C4 rotational symmetry is broken at the (001) surface because the system is only invariant under a four-fold rotation with a translation along the out-of-plane direction. The bulk and (001) surface BZs are shown in Fig. 1d, where high-symmetry points are also noted.

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