A strongly robust type II Weyl fermion semimetal state in Ta ₃ S ₂

Abstract

Weyl semimetals are of great interest because they provide the first realization of the Weyl fermion, exhibit exotic quantum anomalies, and host Fermi arc surface states. The separation between Weyl nodes of opposite chirality gives a measure of the robustness of the Weyl semimetal state. To exploit the novel phenomena that arise from Weyl fermions in applications, it is crucially important to find robust separated Weyl nodes. We propose a methodology to design robust Weyl semimetals with well-separated Weyl nodes. Using this methodology as a guideline, we search among the material parameter space and identify by far the most robust and ideal Weyl semimetal candidate in the single-crystalline compound tantalum sulfide (Ta 3 S 2 ) with new and novel properties beyond TaAs. Crucially, our results show that Ta 3 S 2 has the largest k-space separation between Weyl nodes among known Weyl semimetal candidates, which is about twice larger than the measured value in TaAs and 20 times larger than the predicted value in WTe 2 . Moreover, all Weyl nodes in Ta 3 S 2 are of type II. Therefore, Ta 3 S 2 is a type II Weyl semimetal. Furthermore, we predict that increasing the lattice by <4% can annihilate all Weyl nodes, driving a novel topological metal-to-insulator transition from a Weyl semimetal state to a topological insulator state. The robust type II Weyl semimetal state and the topological metal-to-insulator transition in Ta 3 S 2 are potentially useful in device applications. Our methodology can be generally applied to search for new Weyl semimetals.

Multiple Types of Topological Fermions in Transition Metal Silicides

“…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].…”

Weyl semimetals, Fermi arcs and chiral anomalies

“…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 . …”

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

“…Moreover, Mo x W 1− x Te 2 offers the possiblity to realize a tunable Weyl semimetal, which may be important for transport measurements and applications. Recently, it was also discovered theoretically that WTe 2 hosts a novel type of strongly Lorentz-violating Weyl fermion, or Type II Weyl fermion, long ignored in quantum field theory233132333435363738. This offers a fascinating opportunity to realize in a crystal an emergent particle forbidden as a fundamental particle in particle physics.…”