Abstract
Topologically non-trivial electronic structure is a feature of many rare-earth half-Heusler alloys, which host atoms with high spin-orbit coupling bringing in the non-triviality. In this article, using the first-principles simulations, rare-earth half-Heusler YPdBi, ScPdBi, LaPdBi, LuPdBi, YPtBi and LuPtBi alloys are studied under strain to reveal multiple band inversions associated with topological phase transitions. From our simulations we find that, as a result of first band-inversion, the Brillouin zone of the diamagnetic half-Heusler alloys hosts eight triple points whereas, the second band inversion causes the emergence of sixteen more triple points. These band-inversions are observed to be independent of the spin-orbit coupling and are the reason behind increasing occupation of bismuth 7s orbitals as volume of the unit cell increases. The surface electronic transport in different triple point semi-metallic phases is found to evolve under strain, as the number of Fermi arcs change due to multiple band inversions. Once the second band inversion occurs, further application of tensile strain does not increase the number of triple points and Fermi arcs. However, increasing tensile strain (or decreasing compressive strain) pushes the triple point crossing to higher momenta, making them more effective as source of highly mobile electrons. These observations make a pathway to tune the bulk as well as surface transport through these semi-metals by application of tensile or compressive strain depending on the unstrained relative band-inversion strength of the material.
Highlights
Half-Heusler alloys have come to the limelight in the area of novel materials research as they have shown evidence of multiple new functionalities such as antiferromagnetic spintronics[1,2,3], thermo-electric effects[4,5,6,7], topological non-triviality of electronic b ands[8,9,10], etc
In some of the rare-earth half-Heusler alloys like YPdBi, ScPdBi and LaPdBi, the relativistic splitting itself is not sufficient to create a band-inversion[16,17,18]. These semiconductors are, reported to show a band-inversion at Ŵ point under uniform tensile s train[19]. These findings invite further studies on strained-induced topological phase transition in half-Heusler alloys, which can provide answers to the following questions: (1) can rare-earth diamagnets such as YPdBi, ScPdBi and LaPdBi host topolologically protected Fermions? (2) what is the mechanism associated with this strain-induced phase transition in half-Heusler alloys? (3) can there be multiple band inversions? (4) how does the topologically protected triple-point Fermions evolve under strain?, and (5) how does this strain-induced transition affect the bulk and surface conductivities in these materials?
We have carried out density functional theoy based first-principles study on the strain-induced topological nontriviality in rare-earth half-Heusler YPdBi, ScPdBi, LaPdBi, LuPdBi, YPtBi and LuPtBi alloys
Summary
Half-Heusler alloys have come to the limelight in the area of novel materials research as they have shown evidence of multiple new functionalities such as antiferromagnetic spintronics[1,2,3], thermo-electric effects[4,5,6,7], topological non-triviality of electronic b ands[8,9,10], etc. In some of the rare-earth half-Heusler alloys like YPdBi, ScPdBi and LaPdBi, the relativistic splitting itself is not sufficient to create a band-inversion[16,17,18] These semiconductors are, reported to show a band-inversion at Ŵ point under uniform tensile s train[19]. These findings invite further studies on strained-induced topological phase transition in half-Heusler alloys, which can provide answers to the following questions: (1) can rare-earth diamagnets such as YPdBi, ScPdBi and LaPdBi host topolologically protected Fermions? From our simulations we observed that the strain tuned diamagnetic rare-earth half-Heusler alloys can obtain different triple point semi-metallic phases, which provides a mechanism to control the bulk and surface electronic transport through the materials
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