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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

Weyl points and topological chiral charges in TaAs.(a) In the absence of spin–orbit coupling, there are two line nodes on the kx=0 mirror plane, Mx, and two line nodes on the ky=0 mirror plane, My. In the presence of spin–orbit coupling, each line node vaporizes into six Weyl points. The Weyl points are denoted by small circles. Black and white show the opposite chiral charges of the Weyl points. (b) The band structure around one of the red line nodes in the absence of spin–orbit coupling. (c) The band structure near one of the Weyl points at kxa=0.01π in the presence of spin–orbit coupling. The Weyl point is shifted away from the kx=0 mirror plane. (d) The projection of the bulk Weyl points around the  line. (e) A schematic for the projection of all the Weyl points on the (001) surface Brillouin zone. We denote the eight Weyl points that are located on the kz=2π/c plane as W1 (1) and the other sixteen Weyl points as W2 (2). (f) Calculated spin texture (Sy,Sz) in the vicinity of two Weyl points with opposite chiral charges.
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f3: Weyl points and topological chiral charges in TaAs.(a) In the absence of spin–orbit coupling, there are two line nodes on the kx=0 mirror plane, Mx, and two line nodes on the ky=0 mirror plane, My. In the presence of spin–orbit coupling, each line node vaporizes into six Weyl points. The Weyl points are denoted by small circles. Black and white show the opposite chiral charges of the Weyl points. (b) The band structure around one of the red line nodes in the absence of spin–orbit coupling. (c) The band structure near one of the Weyl points at kxa=0.01π in the presence of spin–orbit coupling. The Weyl point is shifted away from the kx=0 mirror plane. (d) The projection of the bulk Weyl points around the line. (e) A schematic for the projection of all the Weyl points on the (001) surface Brillouin zone. We denote the eight Weyl points that are located on the kz=2π/c plane as W1 (1) and the other sixteen Weyl points as W2 (2). (f) Calculated spin texture (Sy,Sz) in the vicinity of two Weyl points with opposite chiral charges.

Mentions: In order to better understand the Weyl points in TaAs, we first examine the band crossings near the Fermi level in the absence of spin–orbit coupling. These band crossings take the form of a closed curve, or line node, on the Mx and My mirror planes of the BZ, shown in red and blue in Fig. 3a. We present the band structure near one of the red nodal lines, on the Mx mirror plane, in Fig. 3b. The conduction and valence bands dip into each other, giving rise to a line node crossing. Next, we include spin–orbit coupling. This causes each line node to vaporize into six Weyl points shifted slightly away from the mirror planes, shown as small circles in Fig. 3a. There are 24 Weyl points in total: 8 Weyl points on the kz=2π/c plane, which we call W1, and 16 Weyl points away from the kz=2π/c plane, which we call W2. We present the band structure near one of the Weyl points W1 in Fig. 3c, where a point band touching is clearly observed. We have calculated the momentum space locations of the Weyl nodes for the entire TaAs family. The k-space location for Weyl node W1 is (0.0072, 0.5173, 0), (0.0074, 0.5191, 0), (0.0025, 0.4884, 0) and (0.0028, 0.4901, 0) for TaAs, TaP, NbAs and NbP in the unit of (2π/a, 2π/a, 2π/c), respectively. The k-space location for Weyl node W2 is (0.0185, 0.2831, 0.6000), (0.0156, 0.2743, 0.5958), (0.0062, 0.2800, 0.5816) and (0.0049, 0.2703, 0.5750) for TaAs, TaP, NbAs and NbP in the same unit, respectively.


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)

Weyl points and topological chiral charges in TaAs.(a) In the absence of spin–orbit coupling, there are two line nodes on the kx=0 mirror plane, Mx, and two line nodes on the ky=0 mirror plane, My. In the presence of spin–orbit coupling, each line node vaporizes into six Weyl points. The Weyl points are denoted by small circles. Black and white show the opposite chiral charges of the Weyl points. (b) The band structure around one of the red line nodes in the absence of spin–orbit coupling. (c) The band structure near one of the Weyl points at kxa=0.01π in the presence of spin–orbit coupling. The Weyl point is shifted away from the kx=0 mirror plane. (d) The projection of the bulk Weyl points around the  line. (e) A schematic for the projection of all the Weyl points on the (001) surface Brillouin zone. We denote the eight Weyl points that are located on the kz=2π/c plane as W1 (1) and the other sixteen Weyl points as W2 (2). (f) Calculated spin texture (Sy,Sz) in the vicinity of two Weyl points with opposite chiral charges.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Weyl points and topological chiral charges in TaAs.(a) In the absence of spin–orbit coupling, there are two line nodes on the kx=0 mirror plane, Mx, and two line nodes on the ky=0 mirror plane, My. In the presence of spin–orbit coupling, each line node vaporizes into six Weyl points. The Weyl points are denoted by small circles. Black and white show the opposite chiral charges of the Weyl points. (b) The band structure around one of the red line nodes in the absence of spin–orbit coupling. (c) The band structure near one of the Weyl points at kxa=0.01π in the presence of spin–orbit coupling. The Weyl point is shifted away from the kx=0 mirror plane. (d) The projection of the bulk Weyl points around the line. (e) A schematic for the projection of all the Weyl points on the (001) surface Brillouin zone. We denote the eight Weyl points that are located on the kz=2π/c plane as W1 (1) and the other sixteen Weyl points as W2 (2). (f) Calculated spin texture (Sy,Sz) in the vicinity of two Weyl points with opposite chiral charges.
Mentions: In order to better understand the Weyl points in TaAs, we first examine the band crossings near the Fermi level in the absence of spin–orbit coupling. These band crossings take the form of a closed curve, or line node, on the Mx and My mirror planes of the BZ, shown in red and blue in Fig. 3a. We present the band structure near one of the red nodal lines, on the Mx mirror plane, in Fig. 3b. The conduction and valence bands dip into each other, giving rise to a line node crossing. Next, we include spin–orbit coupling. This causes each line node to vaporize into six Weyl points shifted slightly away from the mirror planes, shown as small circles in Fig. 3a. There are 24 Weyl points in total: 8 Weyl points on the kz=2π/c plane, which we call W1, and 16 Weyl points away from the kz=2π/c plane, which we call W2. We present the band structure near one of the Weyl points W1 in Fig. 3c, where a point band touching is clearly observed. We have calculated the momentum space locations of the Weyl nodes for the entire TaAs family. The k-space location for Weyl node W1 is (0.0072, 0.5173, 0), (0.0074, 0.5191, 0), (0.0025, 0.4884, 0) and (0.0028, 0.4901, 0) for TaAs, TaP, NbAs and NbP in the unit of (2π/a, 2π/a, 2π/c), respectively. The k-space location for Weyl node W2 is (0.0185, 0.2831, 0.6000), (0.0156, 0.2743, 0.5958), (0.0062, 0.2800, 0.5816) and (0.0049, 0.2703, 0.5750) for TaAs, TaP, NbAs and NbP in the same unit, respectively.

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