Energy-Dependent Chirality Effects in Quasifree-Standing Graphene

Dombrowski, Daniela; Jolie, Wouter; Petrović, Marin; Runte, Sven; Craes, Fabian; Klinkhammer, Jürgen; Kralj, Marko; Lazić, Predrag; Sela, Eran; Busse, Carsten

doi:10.1103/physrevlett.118.116401

Cited by 26 publications

(32 citation statements)

References 29 publications

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“…2) due to the presence of low energy van Hove singularities or quasi-localized states which can be seen in Fig. 7(c), similar to the experimentally confirmed 56 broken chirality close to the van Hove singularities of monolayer graphene. Vacancies will therefore have a strong effect and suppress the conductivity at all energies, even at the Dirac point, as can be seen Fig.…”

Section: Disorder Effectssupporting

confidence: 80%

DC conductivity of twisted bilayer graphene: Angle-dependent transport properties and effects of disorder

Anđelković

Covaci

Peeters

2018

Phys. Rev. Materials

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The in-plane DC conductivity of twisted bilayer graphene (TBLG) is calculated using an expansion of the real-space Kubo-Bastin conductivity in terms of Chebyshev polynomials. We investigate within a tight-binding (TB) approach the transport properties as a function of rotation angle, applied perpendicular electric field and vacancy disorder. We find that for high-angle twists, the two layers are effectively decoupled, and the minimum conductivity at the Dirac point corresponds to double the value observed in monolayer graphene. This remains valid even in the presence of vacancies, hinting that chiral symmetry is still preserved. On the contrary, for low twist angles, the conductivity at the Dirac point depends on the twist angle and is not protected in the presence of disorder. Furthermore, for low angles and in the presence of an applied electric field, we find that the chiral boundary states emerging between AB and BA regions contribute to the DC conductivity, despite the appearance of localized states in the AA regions. The results agree qualitatively with recent transport experiments in low-angle twisted bilayer graphene.

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Section: Disorder Effectssupporting

confidence: 80%

DC conductivity of twisted bilayer graphene: Angle-dependent transport properties and effects of disorder

Anđelković

Covaci

Peeters

2018

Phys. Rev. Materials

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“…While our numerical calculations of the spectral function and DOS presented below are based on the full matrix form of the GF in Eq. (22), it is instructive to assume a diagonal form of the self-energy and GF,…”

Section: Quasiparticle Spectrum and Scatteringmentioning

confidence: 99%

“…31,33,140,141 In a recent work on disordered Li-decorated graphene, 88 we demonstrated that in T -matrix descriptions of adatoms (we expect that the same holds for other types of adatoms and adsorbates), it is essential to express the T matrix and the Dyson equation in Eqs. (19) and (22) in a "complete" Bloch-state basis; i.e., the basis must include bands which describe the electronic structure of both graphene and the surface region where the adatoms are located.…”

Section: Adatoms and Adsorbatesmentioning

confidence: 99%

Atomistic T -matrix theory of disordered two-dimensional materials: Bound states, spectral properties, quasiparticle scattering, and transport

Kaasbjerg

2020

Phys. Rev. B

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In this work, we present an atomistic first-principles framework for modeling the low-temperature electronic and transport properties of disordered two-dimensional (2D) materials with randomly distributed point defects (impurities). The method is based on the T -matrix formalism in combination with realistic density-functional theory (DFT) descriptions of the defects and their scattering matrix elements. From the T -matrix approximations to the disorder-averaged Green's function (GF) and the collision integral in the Boltzmann transport equation, the method allows calculations of, e.g., the density of states (DOS) including contributions from bound defect states, the quasiparticle spectrum and the spectral linewidth (scattering rate), and the conductivity/mobility of disordered 2D materials. We demonstrate the method by examining these quantities in monolayers of the archetypal 2D materials graphene and transition metal dichalcogenides (TMDs) contaminated with vacancy defects and substitutional impurity atoms. By comparing the Born and T -matrix approximations, we also demonstrate a strong breakdown of the Born approximation for defects in 2D materials manifested in a pronounced renormalization of, e.g., the scattering rate by the higherorder T -matrix method. As the T -matrix approximation is essentially exact for dilute disorder, i.e., low defect concentrations (c dis 1) or density (n dis A −1 cell where A cell is the unit cell area), our first-principles method provides an excellent framework for modeling the properties of disordered 2D materials with defect concentrations relevant for devices. arXiv:1911.00530v1 [cond-mat.mes-hall] 1 Nov 2019

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“…In MoS 2 with almost isotropic energy contours, ε(k) = ε, intravalley backscattering with q = 2k therefore produces circular features. Trigonal warping of the constant energy surfaces gives rise to additional approximate nesting vectors which produce starlike patterns with hexagonal symmetry around the Γ point and triangular symmetry near the K, K points as in graphene [30]. feature because intravalley processes in the K and K valleys add up, while the two K ↔ K intervalley processes have distinct wave vectors, q ≈ ±K.…”

mentioning

confidence: 99%

“…The measured STS map is a probe of the local density of states (LDOS) whose real-space modulation, resembling Friedel oscillations, originates from quasiparticle interference (QPI) between electronic waves scattered by defects. Hence, the Fourier transform of the STS map provides direct access to the available scattering channels in q space, and has shed important light on defect scattering in, e.g., graphene [23][24][25][26][27][28][29][30], monolayer TMDs [18,19], and black phosphorus [31].…”

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confidence: 99%

Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

et al. 2017

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Intervalley scattering by atomic defects in monolayer transition metal dichalcogenides (TMDs; M X2) presents a serious obstacle for applications exploiting their unique valley-contrasting properties. Here, we show that the symmetry of the atomic defects can give rise to an unconventional protection mechanism against intervalley scattering in monolayer TMDs. The predicted defectdependent selection rules for intervalley scattering can be verified via Fourier transform scanning tunneling spectroscopy (FT-STS), and provide a unique identification of, e.g., atomic vacancy defects (M vs X). Our findings put the absence of the intervalley FT-STS peak in recent experiments in a different perspective.Introduction.-Two-dimensional (2D) monolayers of transition metal dichalcogenides (TMDs; M X 2 ) are promising candidates for spin-and valleytronics applications [1]. Their hallmarks include unique valleycontrasting properties and strong spin-valley coupling [1, 2] exemplified by, e.g., valley-selective optical pumping [3][4][5], a valley-dependent Zeeman effect [6][7][8][9], and the valley Hall effect [10]. Such means to control the valley degree of freedom are instrumental for valleytronics applications.Another prerequisite for a successful realization of valleytronics is a sufficiently long valley lifetime [11,12]; atomic defects are a common limiting factor which can provide the required momentum for intervalley scattering due to their short-range nature. However, as illustrated in Fig. 1(a), the spin-orbit (SO) induced spin-valley coupling in the K, K valleys of 2D TMDs partially protects the valley degree of freedom against relaxation via intervalley scattering by nonmagnetic defects [2]. Due to the small spin-orbit splitting in the conduction band valleys [13,14], only the valence-band valleys fully benefit from this protection. Identification of additional protection mechanisms in the conduction band would hence be advantageous for valleytronics in 2D TMDs.In this work, we demonstrate that besides the spinvalley coupling, the symmetry and position of atomic defects give rise to unconventional selection rules for intervalley quasiparticle scattering in 2D TMDs. As illustrated in Fig. 1(b), we find that for defects with threefold rotational symmetry (C 3 ), e.g., atomic vacancies, intervalley K ↔ K scattering in the conduction band is forbidden for defects centered on the X site while it is allowed for M centered defects. In the valence band, intervalley scattering is forbidden in both cases. Analogous selection rules for the intervalley coupling due to confinement potentials in 2D TMD based quantum dots have previously been noted [15].Our findings can be readily verified with scanning tunneling spectroscopy (STS) which has provided valuable insight to the electronic properties of 2D TMDs [16][17][18][19][20]. In particular, Fourier transform STS (FT-STS) is a powerful method for investigating atomic defects and their scattering properties in 2D materials [21,22]. The measured STS map is a probe of the local density ...

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Energy-Dependent Chirality Effects in Quasifree-Standing Graphene

Cited by 26 publications

References 29 publications

DC conductivity of twisted bilayer graphene: Angle-dependent transport properties and effects of disorder

DC conductivity of twisted bilayer graphene: Angle-dependent transport properties and effects of disorder

Atomistic T -matrix theory of disordered two-dimensional materials: Bound states, spectral properties, quasiparticle scattering, and transport

Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

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