Two‐Dimensional Boron Hydride Sheets: High Stability, Massless Dirac Fermions, and Excellent Mechanical Properties

Jiao, Yalong; Ma, Fengxian; Bell, John; Bilić, Ante; Du, Aijun

doi:10.1002/ange.201604369

Cited by 110 publications

(78 citation statements)

References 38 publications

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“…The first behavior is discontinuous Dirac cones; i.e., the number of cones is countable and they are isolated in the BZ, e.g., the predicted P6=mmm boron sheet [43]. The second case is the continuous Dirac cones, which means a high density of Dirac cones exists and they form a ring of Dirac nodes [44] or a Dirac loop as reported before. As a material with multiple cones, MnF 3 is found to be different from both the above.…”

Section: -2mentioning

confidence: 69%

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride

Jiao

Zhang

et al. 2017

Phys. Rev. Lett.

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Spin-polarized materials with Dirac features have sparked great scientific interest due to their potential applications in spintronics. But such a type of structure is very rare and none has been fabricated. Here, we investigate the already experimentally synthesized manganese fluoride (MnF 3 ) as a novel spin-polarized Dirac material by using first-principles calculations. MnF 3 exhibits multiple Dirac cones in one spin orientation, while it behaves like a large gap semiconductor in the other spin channel. The estimated Fermi velocity for each cone is of the same order of magnitude as that in graphene. The 3D band structure further reveals that MnF 3 possesses rings of Dirac nodes in the Brillouin zone. Such a spin-polarized multiple Dirac ring feature is reported for the first time in an experimentally realized material. Moreover, similar band dispersions can be also found in other transition metal fluorides (e.g., CoF 3 , CrF 3 , and FeF 3 ). Our results highlight a new interesting single-spin Dirac material with promising applications in spintronics and information technologies. DOI: 10.1103/PhysRevLett.119.016403 Ever since the spin and charge of one electron have been considered separately, it has been found that the spin current displays superior properties to the classical charge current in the field of information transmission such as high speed, low power consumption, and negligible energy dissipation [1]. Thus, the corresponding spin current has drawn great attention over the past few decades and the spin electronics are rapidly expanding [2][3][4][5][6][7][8][9][10][11]. Up to now, a number of spintronics materials have been proposed including magnetic metals, half-metallic ferromagnets, topological insulators, magnetic semiconductors, diluted magnetic semiconductors, etc. [12][13][14][15][16]. But to exploit the full potential of spintronics in information transfer and storage, some basic issues still remain, such as long distance spin transport, and the generation and injection of spin polarized currents [4,17,18]. In addition to them, the grand challenges for new generation spintronics are how to make electrons transport with ultrahigh speed and consume ultralow energy, which requires realizing massless electrons by discovering the potential Dirac band dispersion, and achieve dissipationless spin transport via generating large spin polarization around the Fermi level [19].It is necessary to emphasize that the well-studied materials for spintronics such as half-metals, can meet the "basic" demand of spintronics applications [20,21]. In addition, Wang [22] proposed a new class of materials named spin gapless semiconductors (SGS) that can generate 100% spin polarized current and is promising in spintronics. The SGS was then validated by Ouardi et al. in experiment [23]. However, to overcome the "grand challenge," the performances of half-metal and SGS are still limited as it just behaves like a metal-semiconductor in one spin orientation, but lacks linear Dirac dispersion, which can hardly reach t...

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Section: -2mentioning

confidence: 69%

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride

Jiao

Zhang

et al. 2017

Phys. Rev. Lett.

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“…As boron has demonstrated striking similarity to carbon, forming planar clusters, [1,[3][4][5][6][7][8] cage-like fullerenes, [9][10][11][12][13][14][15] and 1D nanotubes, [7,[16][17][18][19][20][21][22] extensive theoretical efforts have been devoted to exploring graphene analogs of boron-borophenes. [23][24][25][26][27][28][29] Unlike graphene or hexagonal boron nitride (h-BN), which has exclusively a stable honeycomb lattice, borophene is predicted to the extreme flexibility, the ideal strength of borophene can be over 16 N m −1 , higher than those of the best known polymer materials, and its specific modulus is up to 346 m 2 s −2 , rivaling those of graphene. In contrast to other 2D materials, the borophene can relieve tensile stress by introducing more HHs, manifested as tension-induced lattice phase transitions, and thereby withstand a tensile load of ≈10 N m −1 at strains as high as 40%.…”

Section: Introductionmentioning

confidence: 99%

Elasticity, Flexibility, and Ideal Strength of Borophenes

Zhang

Yang

Penev

et al. 2017

Adv Funct Materials

268

199

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ABSTRACT:We study the mechanical properties of two-dimensional (2D) boron-borophenes -by first-principles calculations. The recently synthesized borophene with 1/6 concentration of hollow hexagons (HH) is shown to have in-plane modulus C up to 210 N/m and bending stiffness as low as D = 0.39 eV. Thus, its Foppl-von Karman number per unit area, defined as C/D, reaches 568 nm -2 , over twofold higher than graphene's value, establishing the borophene as one of the most flexible materials. Yet, the borophene has a specific modulus of 346 m 2 /s 2 and ideal strengths of 16 N/m, rivaling those (453 m 2 /s 2 and 34 N/m) of graphene. In particular, its structural fluxionality enabled by delocalized multi-center chemical bonding favors structural phase transitions under tension, which result in exceptionally small breaking strains yet highly ductile breaking behavior. These mechanical properties can be further tailored by varying the HH concentration, and the boron sheet without HHs can even be stiffer than graphene against tension. The record high flexibility combined with excellent elasticity in boron sheets can be utilized for designing composites and flexible systems.

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“…The conduction and valence bands in graphene touch with linear dispersion at discrete Dirac points on the Fermi level, around which the low-energy electrons behave like relativistic massless Dirac fermions in 2D, exhibiting properties distinct from the usual Schrödinger fermions. Inspired by graphene, much effort has been devoted to the search for other 2D materials which host Dirac/Weyl points, and a number of candidates have been proposed 3 , such as silicene 4,5 , germanene 4,6 , graphyne 7 , 2D carbon and boron allotropes [8][9][10][11][12] , group-VA phosphorene structures 13,14 , and 5d transition metal trichloride 15 . The Dirac points in all these materials (including graphene) are protected by symmetry, but only in the absence of spin-orbit coupling (SOC).…”

Section: Introductionmentioning

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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Two‐Dimensional Boron Hydride Sheets: High Stability, Massless Dirac Fermions, and Excellent Mechanical Properties

Cited by 110 publications

References 38 publications

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride

Elasticity, Flexibility, and Ideal Strength of Borophenes

Two-dimensional spin-orbit Dirac point in monolayer HfGeTe

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