Blue Phosphorene Oxide: Strain-Tunable Quantum Phase Transitions and Novel 2D Emergent Fermions

Zhu, Liyan; Wang, Shan-Shan; Guan, Shaokang; Liu, Ying; Zhang, Tingting; Chen, Guibin; Yang, Shengyuan A.

doi:10.1021/acs.nanolett.6b03208

Cited by 123 publications

(120 citation statements)

References 57 publications

(100 reference statements)

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“…However, for bilayer graphene, there are two such points at BZ corners related by the time reversal symmetry; whereas for ML Na 2 O, there is only one double Weyl point sitting at the BZ center. The double Weyl point endows ML Na 2 O with an interesting optical property, i.e., it should exhibit a universal optical absorbance of πα ≈ 2.3% (α is fine‐structure constant) at low frequencies [for ℏω < ( M 2 – M 1 ) here] …”

Section: Resultsmentioning

confidence: 99%

“…Currently, a target in this direction is to explore new types of band degeneracy points and the associated new emergent fermions. For example, previous works have theoretically proposed 2D massive Dirac fermions, double Weyl fermions, and pseudospin‐1 fermions in some 2D materials, such as blue phosphorene oxide and monolayer (ML) Mg 2 C . However, these proposed materials are not ideal because the emergent fermions are not realized in their equilibrium states.…”

Section: Introductionmentioning

confidence: 99%

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Tunable Topological Energy Bands in 2D Dialkali‐Metal Monoxides

Hua

et al. 2020

Advanced Science

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2D materials with nontrivial energy bands are highly desirable for exploring various topological phases of matter, as low dimensionality opens unprecedented opportunities for manipulating the quantum states. Here, it is reported that monolayer (ML) dialkali‐metal monoxides, in the well‐known 2H‐MoS2 type lattice, host multiple symmetry‐protected topological phases with emergent fermions, which can be effectively tuned by strain engineering. Based on first‐principles calculations, it is found that in the equilibrium state, ML Na2O is a 2D double Weyl semimetal, while ML K2O is a 2D pseudospin‐1 metal. These exotic topological states exhibit a range of fascinating effects, including universal optical absorbance, super Klein tunneling, and super collimation effect. By introducing biaxial or uniaxial strain, a series of quantum phase transitions between 2D double Weyl semimetal, 2D Dirac semimetal, 2D pseudospin‐1 metal, and semiconductor phases can be realized. The results suggest monolayer dialkali‐metal monoxides as a promising platform to explore fascinating physical phenomena associated with novel 2D emergent fermions.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tunable Topological Energy Bands in 2D Dialkali‐Metal Monoxides

Hua

et al. 2020

Advanced Science

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“…For example, 2D quadratic band-touching points have been found in bilayer graphene 59 and in blue phosphorene oxide 60 . It will be interesting to explore these exotic band degeneracy points and their novel physics in future studies.…”

Section: Discussionmentioning

confidence: 99%

Two-dimensional spin-orbit Dirac point in monolayer HfGeTe

Guan

Liu

et al. 2017

Phys. Rev. Materials

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Dirac points in two-dimensional (2D) materials have been a fascinating subject of research, with graphene as the most prominent example. However, the Dirac points in existing 2D materials, including graphene, are vulnerable against spin-orbit coupling (SOC). Here, based on first-principles calculations and theoretical analysis, we propose a new family of stable 2D materials, the HfGeTefamily monolayers, which represent the first example to host so-called spin-orbit Dirac points (SDPs) close to the Fermi level. These Dirac points are special in that they are formed only under significant SOC, hence they are intrinsically robust against SOC. We show that the existence of a pair of SDPs are dictated by the nonsymmorphic space group symmetry of the system, which are very robust under various types of lattice strains. The energy, the dispersion, and the valley occupation around the Dirac points can be effectively tuned by strain. We construct a low-energy effective model to characterize the Dirac fermions around the SDPs. Furthermore, we find that the material is simultaneously a 2D Z2 topological metal, which possesses nontrivial Z2 invariant in the bulk and spin-helical edge states on the boundary. From the calculated exfoliation energies and mechanical properties, we show that these materials can be readily obtained in experiment from the existing bulk materials. Our result reveals HfGeTe-family monolayers as a promising platform for exploring spin-orbit Dirac fermions and novel topological phases in two-dimensions.

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“…and solid-state materials 48 . For massless spin-1 fermion systems without gaps, QHEs have been investigated and it has been found that each spin-1 point contributes an integer Hall conductance 39 .…”

mentioning

confidence: 99%

Unconventional quantum Hall effects in two-dimensional massive spin-1 fermion systems

Duan

2017

Phys. Rev. B

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Unconventional fermions with high degeneracies in three dimensions beyond Weyl and Dirac fermions have sparked tremendous interest in condensed matter physics. Here, we study quantum Hall effects (QHEs) in a two-dimensional (2D) unconventional fermion system with a pair of gapped spin-1 fermions. We find that the original unlimited number of zero energy Landau levels (LLs) in the gapless case develop into a series of bands, leading to a novel QHE phenomenon that the Hall conductance first decreases (or increases) to zero and then revives as an infinite ladder of fine staircase when the Fermi surface is moved toward zero energy, and it suddenly reverses with its sign being flipped due to a Van Hove singularity when the Fermi surface is moved across zero. We further investigate the peculiar QHEs in a dice model with a pair of spin-1 fermions, which agree well with the results of the continuous model.

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Blue Phosphorene Oxide: Strain-Tunable Quantum Phase Transitions and Novel 2D Emergent Fermions

Cited by 123 publications

References 57 publications

Tunable Topological Energy Bands in 2D Dialkali‐Metal Monoxides

Tunable Topological Energy Bands in 2D Dialkali‐Metal Monoxides

Two-dimensional spin-orbit Dirac point in monolayer HfGeTe

Unconventional quantum Hall effects in two-dimensional massive spin-1 fermion systems

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