Band Inversion in Topologically Nontrivial Half-Heusler Bismuthides: <sup>209</sup>Bi NMR Study

Nowak, B.; Pavlosiuk, Orest; Kaczorowski, D.

doi:10.1021/jp5115493

Cited by 18 publications

(24 citation statements)

References 42 publications

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“…The measured 209 Bi isotropic shift is about −6300 ppm for LuPtBi and −4300 ppm for LuPdBi. Similar values for the two compounds measured at the same temperature but at a different magnetic field have been reported 31 , indicating that these values are independent of magnetic field. Upon Pt alloying in LuPd 1-x Pt x Bi, the 209 Bi isotropic shifts change from −4830 ppm for LuPd 0.8 Pt 0.2 Bi, to −6059 ppm for LuPd 0.1 Pt 0.9 Bi.…”

Section: Resultssupporting

confidence: 83%

“…Moreover, nuclear magnetic shielding is sensitive to the change of symmetry of the conduction bands owing to the inversion of the s -like Γ 6 band. Although relativistic effects including SOC on NMR chemical shifts and nuclear spin-spin interactions on small molecules and complexes 21 27 28 and on the surface states of Bi 2 Te 3 24 have already been widely acknowledged and discussed, it is highly desirable for systematic investigation of the relativistic effects on the NMR spectra in heavy half-Heusler intermetallics 29 30 31 . In addition, the underlying mechanism of the correlation between NMR parameters and topologically nontrivial nature remains inconclusive.…”

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confidence: 99%

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NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

Zhang

Hou

Wang

et al. 2016

Sci Rep

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Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by 209Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states.

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Section: Resultssupporting

confidence: 83%

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confidence: 99%

NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

Zhang

Hou

Wang

et al. 2016

Sci Rep

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“…Excitingly, in some half-Heusler phases containing heavy elements (i.e. with strong spin-orbit coupling) an inversion of Γ 8 and Γ 6 bands occurs 5 6 , which is the necessary condition for non-trivial Z 2 topology 7 8 . Therefore half-Heusler phases are promising materials due to coexistence and interplay of AFM, SC and potential topological properties.…”

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confidence: 99%

“…The next stage of the research on half-Heusler phases has been associated with findings of the band inversion in some of them 5 6 18 19 . Observation of SC in some representatives of this family: LaPtBi ( T c = 0.9 K) 20 , LuPtBi (1.0 K) 21 , YPtBi (0.77 K) 22 23 , and LuPdBi (1.7–1.9 K) 24 25 , further increased the interest in their physics, because the simultaneous observation of topological surface states and SC lays the groundwork for realization of Majorana fermion states on the surface of topological superconductors 26 .…”

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confidence: 99%

Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi

Pavlosiuk

Kaczorowski

Fabrèges

et al. 2016

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We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions.

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“…These surface states are topologically protected as long as time-reversal symmetry is preserved, i.e., they are protected against scattering from non-magnetic impurities. Indeed, for some of these materials there is experimental evidence for topologically nontrivial bandstructures and the presence of Dirac surface states [5][6][7], although none were found to be insulating in the bulk. Some compounds from this class were found to be superconductors with critical temperatures up to 1.8 K, e.g.…”

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Unconventional Superconductivity in YPtBi and Related Topological Semimetals

Meinert

2016

Phys. Rev. Lett.

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YPtBi, a topological semimetal with very low carrier density, was recently found to be superconducting below Tc = 0.77 K. In the conventional theory, the nearly vanishing density of states around the Fermi level would imply a vanishing electron-phonon coupling and would therefore not allow for superconductivity. Based on relativistic density functional theory calculations of the electron-phonon coupling in YPtBi it is found that carrier concentrations of more than 10 21 cm −3are required to explain the observed critical temperature with the conventional pairing mechanism, which is several orders of magnitude larger than experimentally observed. It is very likely that an unconventional pairing mechanism is responsible for the superconductivity in YPtBi and related topological semimetals with the Half-Heusler structure.A series of Half-Heusler compounds with heavy elements were predicted to have topologically non-trivial band order [1][2][3]. These compound have high cubic symmetry, however without inversion symmetry. The normal band order with the s-like, twofold degenerate Γ 6 state sitting above the p-like, fourfold degenerate Γ 8 -state is inverted in some of these compounds due to spin-orbit coupling. In their natural state, the cubic symmetry leads to a band degeneracy at Γ around the Fermi level, rendering them semimetals with topologically non-trivial band order (topological semimetals) and very low density of states (DOS) at the Fermi level D(E F ). By breaking the cubic symmetry with some amount of uniaxial strain, the compounds can be made insulating, so they could become 3D topological insulators [4]. They would exhibit metallic surface states with Dirac-like dispersion, i.e., the electrons behave as massless particles with ultrahigh mobility, while at the same time being insulating in the bulk. These surface states are topologically protected as long as time-reversal symmetry is preserved, i.e., they are protected against scattering from non-magnetic impurities. Indeed, for some of these materials there is experimental evidence for topologically nontrivial bandstructures and the presence of Dirac surface states [5][6][7], although none were found to be insulating in the bulk. Some compounds from this class were found to be superconductors with critical temperatures up to 1.8 K, e.g. LaPtBi, LuPtBi, LuPdBi, YPtBi,. Compounds of the type RPdBi (R is a lanthanide with an open 4f shell) that show coexisiting local moment antiferromagnetism as well as superconductivity were found, pointing to the presence of spin triplet Cooper pairs [12], which is allowed due to the missing structural inversion symmetry [13]. Due to the topologically nontrivial band structure, novel collective excitations are possible, in particular surface Majorana fermions [14]. These could provide the basis for low-decoherence quantum processing [15].Superconducting semiconductors such as GeTe and SnTe are long known [16,17] and their superconductivity can be explained [17] with the Eliashberg theory of electron-phonon mediated superc...

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Band Inversion in Topologically Nontrivial Half-Heusler Bismuthides: ²⁰⁹Bi NMR Study

Cited by 18 publications

References 42 publications

NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi

Unconventional Superconductivity in YPtBi and Related Topological Semimetals

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Band Inversion in Topologically Nontrivial Half-Heusler Bismuthides: 209Bi NMR Study

Cited by 18 publications

References 42 publications

NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi

Unconventional Superconductivity in YPtBi and Related Topological Semimetals

Contact Info

Product

Resources

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Band Inversion in Topologically Nontrivial Half-Heusler Bismuthides: ²⁰⁹Bi NMR Study