Quadratic contact point semimetal: Theory and material realization

Zhu, Ziming; Liu, Ying; Yu, Zhi‐Ming; Wang, Shan-Shan; Zhao, Yuxin; Feng, Yuanping; Sheng, Xian‐Lei; Yang, Shengyuan A.

doi:10.1103/physrevb.98.125104

Cited by 64 publications

(18 citation statements)

References 63 publications

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“…Spin-orbit coupling was included for the band-structure calculations. In the case of cubic SnTe, a fourfold degeneracy is observed exactly at the point with a quadratic dispersion along all three directions of the Brillouin zone [33]. The 1.1% out-of-plane tensile strain derived from our structural characterizations pushes the two valence bands into one another, thus creating a pair of unavoided Dirac nodes along the Z (k z ) direction.…”

Section: First-principles Calculationsmentioning

confidence: 75%

Topological band crossings in epitaxial strained SnTe

Fragkos

Sant

Alvarez

et al. 2019

Phys. Rev. Materials

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Epitaxial SnTe (111) is grown by molecular-beam epitaxy on Bi 2 Te 3 substrates. Structural evaluation indicates that SnTe deviates from cubic due to in-plane compressive strain, which induces significant changes in the electronic band structure. More specifically, a pair of gapless crossings between the two uppermost valence bands occurs in k space along the out-of-plane Z direction of the Brillouin zone, associated with a band inversion, thus defining topological three-dimensional Dirac nodes. Combined first-principles calculations and angle-resolved photoelectron spectroscopy reveal an overtilted Dirac cone indicating that the crossing is a topological type-III Dirac node at the borders between type-I and type-II Dirac nodes.

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Section: First-principles Calculationsmentioning

confidence: 75%

Topological band crossings in epitaxial strained SnTe

Fragkos

Sant

Alvarez

et al. 2019

Phys. Rev. Materials

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“…From the pictures, we can see when SOC is included, the gapless semimetal is formed owning to the fourfold degeneracy of Γ8 + , which is also similar to the case of Cu2Se. 45 In Tl2Nb2O7, Γ7 + states are higher than Γ8 + states, while in Cu2Se, Γ8 + states are higher than Γ7 + states.…”

Section: Band Structure and Topological Property Of Strained Tl2nb2o7mentioning

confidence: 85%

Topological phases in pyrochlore thallium niobate Tl2Nb2O6+x

et al. 2019

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The discovery of new topological electronic materials brings a chance to uncover novel physics and plays a key role in observing and controlling various intriguing phenomena. Up to now, many materials have been theoretically proposed and experimentally proved to host different kinds of topological states. Unfortunately, there is little convincing experimental evidence for the existence of topological oxides. The reason is that oxidation of oxygen leads to ionic crystal in general and makes band inversion unlikely. In addition, the realization of different topological states in a single material is quite difficult, but strongly needed for exploring topological phase transitions. In this work, using first-principles calculations and symmetry analysis, we propose that the experimentally tunable continuous solid solution of oxygen in pyrochlore Tl2Nb2O6+x (0 ≤ x ≤ 1.0) leads to various topological states. Topological insulator, Dirac semimetal and triply degenerate nodal point semimetal can be realized in it via changing the oxygen content and/or tuning the crystalline symmetries. When x = 1, it is a semimetal with quadratic band touching point at Fermi level. It transits into a Dirac semimetal or a topological insulator depending on the in-plane strain. When x = 0.5, the inversion symmetry is spontaneously broken in Tl2Nb2O6.5, leading to triply degenerate nodal points. When x = 0, Tl2Nb2O6 becomes a trivial insulator with a narrow band gap. These topological phase transitions driven by solid solution of oxygen are unique and physically plausible due to the variation of valence state of Tl 1+ and Tl 3+ . This topological oxide will be promising for studying correlation induced topological states and potential applications.

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“…To give significance to the observed experimental data, the frequency dependent ac conductivity is modeled in accordance with the literature data which assumes that the ac conductivity (

σ ((), w) = {(σ_{italicTun}^{- 1} + σ_{italicCBH}^{- 1})}^{- 1}

) is governed by the tunneling ( σ Tun ) and correlated barrier hoping ( σ CBH ). The hole tunneling results from the high hole density as the Cu 2 Se is a degenerate semiconductor and also due to the thin metallic slab (50 nm). The tunneling holes conductivity takes the form,

σ ((), w) = \frac{π^{4}}{24} italickT α^{- 1} {(N (E_{F}))}^{2} w R_{w}^{4} .

…”

Section: Resultsmentioning

confidence: 99%

Enhancement of the performance of the Cu₂Se band filters via Yb nanosandwiching

Khusayfan

Qasrawi

Khanfar

2019

Micro & Optical Tech Letters

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In this article, we report the experimental and theoretical modeling on the band pass filters that are made of two thin film layers of Cu 2 Se coated onto aluminum substrates and nanosandwiched with 50 nm ytterbium layers. The nanosandwiching of Yb between two layers of Cu 2 Se is found to decrease the lattice constant, the defect density, and the strain and increase the grain size in the Cu 2 Se. Electrically, it is observed that, Al/Cu 2 Se/Al structure exhibits wave trap characteristics with notch frequency of 1.31 GHz. The Yb-layers improved the performance of the band pass filters by increasing the amplitude of the reflection coefficients, increasing the return loss values and decreasing the voltage standing wave ratios. The calculated conduction and wave trapping parameters nominate the Yb-nanosandwiched Cu 2 Se films for use in communication technology as they exhibit negative capacitance effect and narrow band pass range. K E Y W O R D Sband pass filters, conductivity, Cu 2 Se, negative capacitance, X-ray

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Quadratic contact point semimetal: Theory and material realization

Cited by 64 publications

References 63 publications

Topological band crossings in epitaxial strained SnTe

Topological band crossings in epitaxial strained SnTe

Topological phases in pyrochlore thallium niobate Tl2Nb2O6+x

Enhancement of the performance of the Cu₂Se band filters via Yb nanosandwiching

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Quadratic contact point semimetal: Theory and material realization

Cited by 64 publications

References 63 publications

Topological band crossings in epitaxial strained SnTe

Topological band crossings in epitaxial strained SnTe

Topological phases in pyrochlore thallium niobate Tl2Nb2O6+x

Enhancement of the performance of the Cu2Se band filters via Yb nanosandwiching

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Enhancement of the performance of the Cu₂Se band filters via Yb nanosandwiching