Semimetal with both Rarita-Schwinger-Weyl and Weyl excitations

Liang, Long; Yu, Yue

doi:10.1103/physrevb.93.045113

Cited by 61 publications

(46 citation statements)

References 41 publications

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“…Taken together with calculation, our experimental data show that we have realized the first Type II Weyl semimetal, with strongly Lorentz-violating Weyl fermions. We point out that in contrast to concurrent works on the Weyl semimetal state in MoTe 2 (refs 44, 45, 46, 47, 48, 49, 50, 51, 52), we directly access the unoccupied band structure of Mo x W 1− x Te 2 and directly observe a Weyl semimetal with minimal reliance on calculation. In particular, our observation of a surface state kink at a generic point in the surface Brillouin zone requires that the system be a Weyl semimetal42.…”

Section: Discussionmentioning

confidence: 84%

Discovery of a new type of topological Weyl fermion semimetal state in MoxW1−xTe2

et al. 2016

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The recent discovery of a Weyl semimetal in TaAs offers the first Weyl fermion observed in nature and dramatically broadens the classification of topological phases. However, in TaAs it has proven challenging to study the rich transport phenomena arising from emergent Weyl fermions. The series MoxW1−xTe2 are inversion-breaking, layered, tunable semimetals already under study as a promising platform for new electronics and recently proposed to host Type II, or strongly Lorentz-violating, Weyl fermions. Here we report the discovery of a Weyl semimetal in MoxW1−xTe2 at x=25%. We use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe a topological Fermi arc above the Fermi level, demonstrating a Weyl semimetal. The excellent agreement with calculation suggests that MoxW1−xTe2 is a Type II Weyl semimetal. We also find that certain Weyl points are at the Fermi level, making MoxW1−xTe2 a promising platform for transport and optics experiments on Weyl semimetals.

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Section: Discussionmentioning

confidence: 84%

Discovery of a new type of topological Weyl fermion semimetal state in MoxW1−xTe2

et al. 2016

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“…As a generalization, the spin-1 excitation takes 3 × 3 spin matrices and holds a three-fold degeneracy (see 1(b)), its crossing point carries a topological charge ±2 because of no contribution from the middle band with the helicity 0 [32,33]. Spin-3/2 excitations are named as Rarita-Schwinger-Weyl (RSW) fermions [32,[34][35][36], and S takes 4×4 spin matrices. Its Fermi surface has to cross two bands near the crossing point, for example, the helicity 3/2 band with the Berry phase ±3 and the helicity 1/2 band with the Berry phase ±1 (see Fig.…”

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confidence: 99%

Multiple Types of Topological Fermions in Transition Metal Silicides

Tang¹,

Zhou²,

Zhang³

2017

Phys. Rev. Lett.

412

432

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Exotic massless fermionic excitations with non-zero Berry flux, other than Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as spin-1 excitations with 3-fold degeneracy and spin-3/2 Rarita-Schwinger-Weyl fermions. Herein, by using ab initio density functional theory, we show that these unconventional quasiparticles coexist with type-I and type-II Weyl fermions in a family of transition metal silicides, including CoSi, RhSi, RhGe and CoGe, when the spin-orbit coupling (SOC) is considered. Their non-trivial topology results in a series of extensive Fermi arcs connecting projections of these bulk excitations on side surface, which is confirmed by (010) surface electronic spectra of CoSi. In addition, these stable arc states exist within a wide energy window around the Fermi level, which makes them readily accessible in angle-resolved photoemission spectroscopy measurements.Introduction.-Three types of fermions play fundamental roles in our understanding of nature: Majorana, Dirac and Weyl [1]. Much attention has been paid to looking for these fundamental particles in high energy physics during past few decades, whereas only signature of Dirac fermions is captured. Interestingly, the same movement comes up in the field of condensed matter physics [2], and great achievements have been made in last few years. For example, the Majorana-like excitations are detected in superconducting heterostructures [3][4][5][6]; the Dirac [7][8][9][10][11][12] and Weyl [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] fermions are observed in some compounds. These quasiparticles in solid states are not only important for basic science, but also show great potential for practical applications on new devices [30,31].Because symmetries in condensed matter physics are usually much lower than the Poincaré symmetry in high energy physics, quasiparticles in solid states are less constrained such that various new types of fermionic excitations are predicted to exist in 3D lattices [32]. Among these allowed by space group (SG) symmetries are spin-1 and spin-3/2 massless fermionic excitations, besides the well-known spin-1/2 case, namely the Weyl fermion. All of these massless quasiparticles can be described by the low energy Hamiltonian in a unified manner to the linear order of momentum

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“…However, it is challenging to observe the extremely small Fermi arcs in WTe 2 because of the small separation of the Weyl points (0.7% of the Brillouin zone). Weyl fermions have also been predicted in the low-temperature phase of MoTe 2 with much larger Fermi arcs1011, and signatures of the Fermi arcs have been suggested in a combined angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling spectroscopy study12 and other ARPES studies1314151617. The existence of Weyl fermions has been relied on the assumption that the low-temperature phase of MoTe 2 is isostructural to the noncentrosymmetric T d phase of WTe 2 (refs 10, 11).…”

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confidence: 99%

Raman signatures of inversion symmetry breaking and structural phase transition in type-II Weyl semimetal MoTe2

et al. 2016

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Transition metal dichalcogenide MoTe2 is an important candidate for realizing the newly predicted type-II Weyl fermions, for which the breaking of the inversion symmetry is a prerequisite. Here we present direct spectroscopic evidence for the inversion symmetry breaking in the low-temperature phase of MoTe2 by systematic Raman experiments and first-principles calculations. We identify five lattice vibrational modes that are Raman-active only in the low-temperature noncentrosymmetric structure. A hysteresis is also observed in the peak intensity of inversion symmetry-activated Raman modes, confirming a temperature-induced structural phase transition with a concomitant change in the inversion symmetry. Our results provide definitive evidence for the low-temperature noncentrosymmetric Td phase from vibrational spectroscopy, and suggest MoTe2 as an ideal candidate for investigating the temperature-induced topological phase transition.

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Semimetal with both Rarita-Schwinger-Weyl and Weyl excitations

Cited by 61 publications

References 41 publications

Discovery of a new type of topological Weyl fermion semimetal state in MoxW1−xTe2

Discovery of a new type of topological Weyl fermion semimetal state in MoxW1−xTe2

Multiple Types of Topological Fermions in Transition Metal Silicides

Raman signatures of inversion symmetry breaking and structural phase transition in type-II Weyl semimetal MoTe2

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