Abstract
We discuss first-principles topological electronic structure of noncentrosymmetric SrSi2 materials class based on the hybrid exchange-correlation functional. Topological phase diagram of SrSi2 is mapped out as a function of the lattice constant with focus on the semimetal order. A tunable double-Weyl Fermion state in Sr1−xCaxSi2 and Sr1−xBaxSi2 alloys is identified. Ca doping in SrSi2 is shown to yield a double-Weyl semimetal with a large Fermi arc length, while Ba doping leads to a transition from the topological semimetal to a gapped insulator state. Our study indicates that SrSi2 materials family could provide an interesting platform for accessing the unique topological properties of Weyl semimetals.
Highlights
Based on the energy dispersion around a Weyl node, WSMs are classified into two types
By applying the recently proposed method for determining the chiral charge of a Weyl node lying on a rotation axis[43], we find that W1 has a nonzero chiral charge of +1, while W2 has an equal and opposite charge of −1
We have analyzed the chiral charge by calculating the Berry flux on a closed surface enclosing the Weyl nodes to ascertain that SrSi2 is a Weyl semimetal without the SOC, consistent with the results of Ref.[44]
Summary
Based on the energy dispersion around a Weyl node, WSMs are classified into two types. The transitional-metal monophosphides (TaAs, TaP, NbAs, and NbP) were the first WSMs realized experimentally, and have been explored quite extensively in connection with their unique topological states and transport characteristics[21,22,34,35,36,37] These materials exist in stoichiometric single-crystalline phase, and host a robust WSM state through the breaking of inversion symmetry. The double-WSM state has been predicted recently in the inversion-asymmetric chiral compound strontium disilicide, SrSi2, through band structure calculations[44] This is an interesting material because it is composed of non-toxic and naturally abundant elements, and it has been known for decades as a promising candidate for thermoelectric applications through chemical substitution[48,49,50,51,52,53]. Other experimental studies focusing on thermoelectric properties show that the semimetal state of SrSi2 could be stabilized through chemical substitution of Sr by the lighter Ca atoms[50,51]
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