Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

Xu, Su; Alidoust, Nasser; Chang, Guoqing; Lu, Hong; Singh, Bahadur; Belopolski, Ilya; Sanchez, Daniel S.; Zhang, Xiao; Bian, Guang; Zheng, Hao; Husanu, Marius-Adrian; Bian, Yi; Huang, Shin Ming; Hsu, Chuang‐Han; Chang, Tay Rong; Jeng, Horng Tay; Bansil, Arun; Neupert, Titus; Strocov, Vladimir N.; Lin, Hsin; Jia, Shuang; Hasan, M. Zahid

doi:10.1126/sciadv.1603266

Sci. Adv.

2017

DOI: 10.1126/sciadv.1603266

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Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

Su Xu

Nasser Alidoust

Guoqing Chang

et al.

Abstract: Photoemission revealed the type II Weyl fermionic quasiparticles in LaAlGe crystals.

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Cited by 209 publications

(162 citation statements)

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“…The advantages of this line of research for materials discovery were thoroughly discusses in reference 14 , where the search was based on the Inorganic Crystal Structure Database of FIZ Karlsruhe 27 , which systematically records the lattice structure of crystals that have been synthesized over the course of a century. Following this approach and calculating the band structure of the materials that are likely semimetals, many experimentally feasible Weyl semimetal candidates have been identified 10,14,28,29,34 . …”

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Weyl semimetals, Fermi arcs and chiral anomalies

Jia¹,

Xu²,

Hasan³

2016

Nature Mater

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303

255

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Physicists have discovered a novel topological semimetal, the Weyl semimetal, whose surface features a nonclosed Fermi surface while the low energy quasiparticles in the bulk emerge as Weyl fermions. Here they share a brief review of the development and present perspectives on the next step forward.Weyl semimetals are semimetals or metals whose quasiparticle excitation is the Weyl fermion, a particle that played a crucial role in quantum field theory but has not been observed as a fundamental particle in vacuum 1-24 . Weyl fermions have definite chiralities, either left-handed or right handed. In a Weyl semimetal, the chirality can be understood as a topologically protected chiral charge. Weyl nodes of opposite chirality are separated in momentum space and are connected only through the crystal boundary by an exotic nonclosed surface state, the Fermi arcs. Remarkably, Weyl fermions are robust while carrying currents, giving rise to exceptionally high mobilities. Their spins are locked to their momentum directions due to their character of momentum space magnetic monopole configuration.The presence of parallel electrical and magnetic fields can break the apparent conservation of the chiral charge due to the chiral anomaly, making a Weyl metal, unlike ordinary nonmagnetic metals, more conductive with an increasing magnetic field. These new topological phenomena beyond topological insulators make new physics accessible and suggest potential applications, despite the early stage of the research .In this Commentary, we will review key experimental progress and present an outlook for future directions of the field. Through this article, we hope to expound our perspectives on the key results and the experimental approaches currently used to access the novel physics as well as their limitations. Moreover, while most of the current experiments are still focusing on the discovery of new Weyl materials and demonstration of novel Weyl physics such as the chiral anomaly, it is becoming clear that a crucial step forward is to develop schemes for achieving quantum controls of the novel Weyl physics by electrical and optical means. We discuss some theoretical proposals along these lines highlighting the experimental techniques and matching materials conditions that are necessary for realizing these research directions. 2 MATERIAL SEARCHAlthough the theory of Weyl semimetal has been around for a long time in various forms 1-4 , its discovery had to wait until recent developments. This is because finding experimental realization requires appropriate materials simulation and characterizations. Historically, the first two material predictions, the pyrochlore iridates R 2 Ir 2 O 7 4 and the magnetically doped superlattice 6 , were both on time-reversal breaking (magnetic) materials.Perhaps influenced by the first works, for a long while, the community continued to focus on time-reversal breaking Weyl semimetals materials candidates 7,10 . These candidates were extensively studied by many experimental groups. Unfortunately, these ef...

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“…Shortly after TaAs, a number of new Weyl semimetal candidates along the same line of thinking were proposed. 34,35 .…”

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confidence: 99%

Weyl semimetals, Fermi arcs and chiral anomalies

Jia¹,

Xu²,

Hasan³

2016

Nature Mater

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255

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“…Here, we propose a new strategy to search for magnetic Weyl semimetals. Taking advantage of the Weyl nodes generated by inversion-symmetry breaking in the nonmagnetic compound LaAlGe [44,58], we present a new type of magnetic Weyl semimetal in its iso-structural sister compounds CeAlGe and PrAlGe [59,60] that are ferromagnetic [61][62][63]. We show that the ferromagnetism in RAlGe can be more reliably modeled in first-principles calculation as it is found to not completely change the band structure.…”

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confidence: 99%

“…Upon the inclusion of the spin-orbit coupling, the nodal lines are gapped out and 24 Weyl nodes emerge in the vicinity. We refer to the 8 Weyl nodes located on the k z = 0 plane as W1 and the remaining 16 Weyl nodes away from this plane as W2 [44]. Moreover, each W3 (spinless)…”

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Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlGe family of compounds ( R=rareearth
Chang
¹
,
Singh
²
,
Xu
³

et al. 2018
Phys. Rev. B
Self Cite
167
3
102
0
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Weyl semimetals are novel topological conductors that host Weyl fermions as emergent quasiparticles. In this paper, we propose a new type of Weyl semimetal state that breaks both time-reversal symmetry and inversion-symmetry in the RAlGe (R=Rare earth) family. Compared to previous predictions of magnetic Weyl semimetal candidates, the prediction of Weyl nodes in RAlGe are more robust and less dependent on the details of the magnetism, because the Weyl nodes are already generated by the inversion breaking and the ferromagnetism acts as a simple Zeeman coupling that shifts the Weyl nodes in k space. Moreover, RAlGe offers remarkable tunability, which covers all varieties of Weyl semimetals including type-I, type-II, inversion-breaking and time-reversal breaking, depending on a suitable choice of the rare earth elements. Further, the unique noncentrosymmetric and ferromagnetic Weyl semimetal state in RAlGe enables the generation of spin-currents.

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Band Structure Perfection and Superconductivity in Type‐II Dirac Semimetal Ir₁₋_xPt_xTe₂

Fei

Wang

et al. 2018

Advanced Materials

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The discovery of a new type-II Dirac semimetal in Ir Pt Te with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level close to the Dirac point. The type-II Dirac dispersion in Ir Pt Te is confirmed by angle-resolved photoemission spectroscopy and first-principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir Pt Te is an ideal platform for further studies on the exotic properties and potential applications of type-II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics.

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Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

Abstract: Photoemission revealed the type II Weyl fermionic quasiparticles in LaAlGe crystals.

Cited by 209 publications

References 62 publications

Weyl semimetals, Fermi arcs and chiral anomalies

Weyl semimetals, Fermi arcs and chiral anomalies

Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlGe family of compounds ( R=rareearth
Chang
¹
,
Singh
²
,
Xu
³

et al. 2018
Phys. Rev. B
Self Cite
167
3
102
0
View full text Add to dashboard Cite

Band Structure Perfection and Superconductivity in Type‐II Dirac Semimetal Ir₁₋_xPt_xTe₂

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Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

Abstract: Photoemission revealed the type II Weyl fermionic quasiparticles in LaAlGe crystals.

Cited by 209 publications

References 62 publications

Weyl semimetals, Fermi arcs and chiral anomalies

Weyl semimetals, Fermi arcs and chiral anomalies

Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlGe family of compounds ( R=rareearthChang1, Singh2, Xu3 et al. 2018Phys. Rev. BSelf Cite16731020View full textAdd to dashboardCite

Band Structure Perfection and Superconductivity in Type‐II Dirac Semimetal Ir1−xPtxTe2

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Magnetic and noncentrosymmetric Weyl fermion semimetals in the RAlGe family of compounds ( R=rareearth
Chang
¹
,
Singh
²
,
Xu
³

et al. 2018
Phys. Rev. B
Self Cite
167
3
102
0
View full text Add to dashboard Cite

Band Structure Perfection and Superconductivity in Type‐II Dirac Semimetal Ir₁₋_xPt_xTe₂