Molecular beam epitaxy of three-dimensional Dirac material Sr3PbO

Samal, D.; Nakamura, H.; Takagi, H.

doi:10.1063/1.4955213

Cited by 32 publications

(32 citation statements)

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“…It is also worth noting that experiments on this series of materials are now developing. We have highly refined crystal characterization [28], thin film fabrication [29,30], a thermal measurement [31], and even a report of superconductivity [32].In this paper, we show that the competition between SOC and the band overlap leads to an interesting evolution of the band structure, taking Ba 3 SnO as a prototypical example. In the previous work on the analysis of the antiperovskite family [24], we regarded that the SOC arXiv:1705.08934v1 [cond-mat.mes-hall]…”

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confidence: 84%

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Evolution of band topology by competing band overlap and spin-orbit coupling: Twin Dirac cones in Ba3SnO as a prototype

Kariyado

Ogata

2017

Phys. Rev. Materials

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We theoretically demonstrate how competition between band inversion and spin-orbit coupling (SOC) results in nontrivial evolution of band topology, taking antiperovskite Ba3SnO as a prototype material. A key observation is that when the band inversion dominates over SOC, there appear "twin" Dirac cones in the band structure. Due to the twin Dirac cones, the band shows highly peculiar structure in which the upper cone of one of the twin continuously transforms to the lower cone of the other. Interestingly, the relative size of the band inversion and SOC is controlled in this series of antiperovskite A3EO by substitution of A (Ca, Sr, Ba) and/or E (Sn, Pb) atoms. Analysis of an effective model shows that the emergence of twin Dirac cones is general, which makes our argument a promising starting point for finding a singular band structure induced by the competing band inversion and SOC.Singularities in band structures give rise to singular and attracting responses of materials [1][2][3][4][5]. Therefore, significant amount of efforts have been paid on finding what kinds of singularities are possible in principle, and on proposing materials to realize the singularities, both in theory and experiments [6][7][8]. The "standard" singularity is Dirac/Weyl cone [9-13], which is characterized by a linear, or conical dispersion around an isolated gapclosing point in the Brillouin zone. Already a number of materials are confirmed to possess Dirac/Weyl cones, ranging from graphene [14] (two-dimensional) to Cd 3 As 2 [15], Na 3 Bi [16], and TaAs [17] (three-dimensional), and so on. However, the linear dispersion around the isolated gap-closing point is not the only possible band singularity. The gap-closing point can form a line (typically a loop) in the Brillouin zone rather than an isolated point [18][19][20]. Also, a dispersion around a gap-closing point can be quadratic rather than linear [21]. Very recently, singularities involving three bands are also discussed [22,23].Quite often, the three ingredients, i.e., band inversion, spin-orbit coupling (SOC), and symmetry, play key roles in generating a singular band structure. Roughly speaking, the band inversion means an overlap between two bands with different origin, typically originating from different kinds of orbitals, say s-and p-orbitals, or p-and d-orbitals. Naively, the overlapped bands repel with each other (band anticrossing). However the gap opening due to the band repulsion is sometimes prohibited by some symmetry, leading to singular gap closing points. The SOC, on the other hand, determines which kinds of the band repulsion is allowed, in other words, what kinds of gap-closing points can appear. terial Ca 3 PbO is predicted to have three-dimensional Dirac cones exactly at the Fermi energy, and importantly, all of the three ingredients, the band overlap, SOC, and the symmetry, are relevant in the formation of Dirac cones. (Strictly speaking, there is a tiny mass gap. If we make an emphasis on the gapful nature, the system is a topological crystalline insulator ...

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confidence: 84%

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confidence: 99%

Evolution of band topology by competing band overlap and spin-orbit coupling: Twin Dirac cones in Ba3SnO as a prototype

Kariyado

Ogata

2017

Phys. Rev. Materials

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“…Since the samples reported in this work were grown at different times spanning a two-year period, different growth parameters were used in the course of optimizing film quality (example parameters can be found in Refs. [20,25]). We will not focus on these systematic differences, but instead on the ubiquitous observation of an antiperovskite phase via XPS.…”

Section: Films Of Sr 3 Sno and Srmentioning

confidence: 99%

“…Following growth, the films were examined in situ using reflection high-energy electron diffraction (RHEED), then transferred in vacuum suitcases (Ferrovac GmbH; pressure range: low 10 −10 mbar) for XPS measurements. We note that other films grown with identical conditions to these ones were capped with Au or Apiezon-N grease in an Ar glove box then characterized by X-ray diffraction (XRD) and/or transport [20,25].…”

Section: Films Of Sr 3 Sno and Srmentioning

confidence: 99%

Unusual valence state in the antiperovskites Sr3SnO and Sr3PbO revealed by x-ray photoelectron spectroscopy

Huang

Nakamura

Küster

et al. 2019

Phys. Rev. Materials

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The class of antiperovskite compounds A3BO (A = Ca, Sr, Ba; B = Sn, Pb) has attracted interest as a candidate 3D Dirac system with topological surface states protected by crystal symmetry. A key factor underlying the rich electronic structure of A3BO is the unusual valence state of B, i.e., a formal oxidation state of −4. Practically, it is not obvious whether anionic B can be stabilized in thin films, due to its unusual chemistry, as well as the polar surface of A3BO, which may render the growth-front surface unstable. We report X-ray photoelectron spectroscopy (XPS) measurements of single-crystalline films of Sr3SnO and Sr3PbO grown by molecular beam epitaxy (MBE). We observe shifts in the core-level binding energies that originate from anionic Sn and Pb, consistent with density functional theory (DFT) calculations. Near the surface, we observe additional signatures of neutral or cationic Sn and Pb, which may point to an electronic or atomic reconstruction with possible impact on putative topological surface states. * d.huang@fkf.mpg.de † hnakamur@uark.edu; Present address:

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“…Both of these Dirac nodes (D1 and D2) are located along the Γ-X lines in the Brillouin zone with six copies of each due to cubic symmetry. Sr 3 SnO films were grown by a molecular beam epitaxy [30]. The growth was performed on YSZ (Yttria stablized ZrO 2 ) substrates at a substrate temperature of 450 • C. The grown films were single-crystalline with no impurity phase in the X-ray diffraction (see Supplemental Material [35]).…”

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Robust weak antilocalization due to spin-orbital entanglement in Dirac material Sr3SnO

et al. 2020

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The presence of both inversion (P ) and time-reversal (T ) symmetries in solids leads to well-known double degeneracy of electronic bands (Kramers degeneracy). When the degeneracy is lifted, spin textures can be directly observed in momentum space, as in topological insulators or in strong Rashba materials. The existence of spin textures with Kramers degeneracy, however, is very difficult to observe directly. Here, we use quantum interference measurements combined with first-principle band structure calculations to provide evidence for the existence of hidden entanglement between spin and momentum in antiperovskite-type 3D Dirac material Sr3SnO. We find robust weak antilocalization (WAL) independent of the position of EF, whereas clear signature of weak localization (WL) develops only when EF shifts away from the Dirac node by doping. The observed WAL signal at low doping is fitted using a single interference channel which implies that the different Dirac valleys are mixed by disorder. Notably, this mixing does not suppress WAL, suggesting contrasting interference physics compared to graphene. We identify scattering among axially spin-momentum locked states as a key process that leads to a spin orbital entanglement, giving rise to robust WAL. Our work sheds light on the subtle role of spin and pseudospin when both could contribute to the same quantum effect. arXiv:1806.08712v1 [cond-mat.mes-hall]

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Molecular beam epitaxy of three-dimensional Dirac material Sr3PbO

Cited by 32 publications

References 25 publications

Evolution of band topology by competing band overlap and spin-orbit coupling: Twin Dirac cones in Ba3SnO as a prototype

Evolution of band topology by competing band overlap and spin-orbit coupling: Twin Dirac cones in Ba3SnO as a prototype

Unusual valence state in the antiperovskites Sr3SnO and Sr3PbO revealed by x-ray photoelectron spectroscopy

Robust weak antilocalization due to spin-orbital entanglement in Dirac material Sr3SnO

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