Observation of Weyl nodes and Fermi arcs in tantalum phosphide

Abstract

A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs.

Singularities in the Andreev spectrum of a multiterminal Josephson junction

“…In a 3D solid, the SO interaction and the inversion-symmetry breaking are essential for occurrence stable Weyl point [19][20][21] . Very recently, the angle-resolved photoemission spectroscopy experiments confirmed the existence of the Weyl points in the 3D solids, such as TaAs [22][23][24] , TaP 25 , and NbAs 26 .…”

Nearly massless Dirac fermions and strong Zeeman splitting in the nodal-line semimetal ZrSiS probed by de Haas–van Alphen quantum oscillations

“…When the spin degeneracy is lifted by broken time-reversal or spatial inversion symmetry, a Dirac state evolves to a Weyl state where each Dirac cone splits to a pair of Weyl cones with opposite chirality [1,3,[7][8]. The inversion symmetry broken Weyl states were demonstrated in transition metal monopnictides (Ta/Nb)(As/P) [7][8][9][10][11][12][13][14], photonic crystals [17], and (W/Mo)Te 2 [18][19][20][21][22][23][24][25][26][27]. The spontaneous time reversal symmetry breaking Weyl state has been reported in YbMnBi 2 [28] and predicted in magnetic Heusler alloys [29][30][31][32][33] and the magnetic members of R-Al-X (R=rare earth, X=Si, Ge) compounds [34].…”

“…The recent discoveries of three-dimensional (3D) topological Dirac and Weyl semimetals [1][2][3][4][5][6][7][8][9][10][11][12][13][14] have stimulated enormous interest. These materials are characterized by symmetryprotected discrete band touching points in the momentum space, at which the electron energy bands display linear crossing near the Fermi level [1,3,[7][8].…”

Observation of Fermi-Arc Spin Texture in TaAs

“…While the Weyl fermion as a fundamental particle remains evasive after its prediction 86 years ago [1], the low-energy Weyl fermion quasiparticle has been recently predicted theoretically [2,3] and observed experimentally in TaAs [4][5][6][7] and related materials [8][9][10][11][12]. These so-called Weyl semimetals (WSMs) possess pairs of Weyl nodes with opposite chirality in the bulk.…”