Failure of Conductance Quantization in Two-Dimensional Topological Insulators due to Nonmagnetic Impurities

Novelli, Pietro; Taddei, F.; Geǐm, A. K.; Polini, Marco

doi:10.1103/physrevlett.122.016601

Cited by 77 publications

(61 citation statements)

References 57 publications

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“…It is interesting to notice that a similar mechanism has been proposed very recently in the framework of the Kane-Mele-Hubbard model in graphene, where the breakdown of time reversal symmetry at vacancy defects is shown to lead to a corresponding breakdown of conductance quantization 23 . The present ab-initio calculations support this picture and also bear similarities with simple theoretical models in which magnetic scatterers, such as magnetic adatoms or ferromagnetic gates, are introduced in 2D TIs 39,40 .…”

Section: Breakdown Of Edge Transmission Due To Magnetic Edge Defsupporting

confidence: 52%

Conductance of quantum spin Hall edge states from first principles: The critical role of magnetic impurities and inter-edge scattering

2020

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The outstanding transport properties expected at the edge of two-dimensional time-reversal invariant topological insulators have proven to be challenging to realize experimentally, and have so far only been demonstrated in very short devices. In search for an explanation to this puzzling observation, we here report a full first-principles calculation of topologically protected transport at the edge of novel quantum spin Hall insulators -specifically, Bismuth and Antimony halidesbased on the non-equilibrium Green's functions formalism. Our calculations unravel two different scattering mechanisms that may affect two-dimensional topological insulators, namely time-reversal symmetry breaking at vacancy defects and inter-edge scattering mediated by multiple co-operating impurities, possibly non-magnetic. We discuss their drastic consequences for typical non-local transport measurements as well as strategies to mitigate their negative impact. Finally, we provide an instructive comparison of the transport properties of topologically protected edge states to those of the trivial edge states in MoS2 ribbons. Although we focus on a few specific cases (in terms of materials and defect types) our results should be representative for the general case and thus have significance beyond the systems studied here.

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Section: Breakdown Of Edge Transmission Due To Magnetic Edge Defsupporting

confidence: 52%

Conductance of quantum spin Hall edge states from first principles: The critical role of magnetic impurities and inter-edge scattering

2020

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“…However, there remain a few challenges to practical applications of TQMs. For example, the challenge in the development of TIs [1][2][3][4][5] , one of the most widely studied classes of topological materials, is to protect their key features against disorders or defects that may destroy their quantized conductance 6,7 . On the other hand, the discovery of Chern insulators [8][9][10][11] with broken time-reversal symmetry is a challenge because of the incompatibility between ferromagnetism and electronic insulation.…”

Section: Introductionmentioning

confidence: 99%

Cobalt-based magnetic Weyl semimetals with high-thermodynamic stabilities

et al. 2021

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Recent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co)-based shandite and alloys, Co3MM’X2 (M/M’ = Ge, Sn, Pb, X = S, Se, Te), and identify stable structures with different Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl points and their types are mainly governed by the interaction between Co and the metal atoms, Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological phases, depending on the relative positions of the Sn and Pb atoms: a three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous Hall conductivity (~1290 Ω−1 cm−1) that is larger than that of Co2Sn2S2. Our work reveals the physical mechanism of the origination of Weyl fermions in Co-based shandite structures and proposes topological quantum states with high thermal stability.

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“…It is worth mentioning that imperfectly quantized twoterminal G(E F ) was observed in early experiments on QSHI [19], provoking a lively search for exotic many-body inelastic effects [20][21][22][23][24][25][26] which can circumvent band-topology constraints and introduce backscattering of electrons as they propagate through edge states. On the other hand, Fig.…”

Section: Introductionmentioning

confidence: 99%

Robustness of quantized transport through edge states of finite length: Imaging current density in Floquet topological versus quantum spin and anomalous Hall insulators

Bajpai

Nikolić

2020

Phys. Rev. Research

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The theoretical analysis of topological insulators (TIs) has been traditionally focused on infinite homogeneous crystals with band gap in the bulk and nontrivial topology of their wave functions, or infinite wires whose boundaries host surface or edge metallic states. Such infinite-length edge states exhibit quantized conductance which is insensitive to edge disorder, as long as it does not break the underlying symmetry or introduce energy scale larger than the bulk gap. However, experimental devices contain finite-size topological region attached to normal metal (NM) leads, which poses a question about how precise is quantization of longitudinal conductance and how electrons transition from topologically trivial NM leads into the edge states. This particularly pressing issue for recently conjectured two-dimensional (2D) Floquet TI where electrons flow from time-independent NM leads into time-dependent edge states, the very recent experimental realization [J. W. McIver et al., Nat. Phys. 16, 38 (2020)] of Floquet TI using graphene irradiated by circularly polarized light did not exhibit either quantized longitudinal or Hall conductance. Here, we employ a charge-conserving solution for Floquet-nonequilibrium Green functions of irradiated graphene nanoribbon to compute longitudinal two-terminal conductance, as well as spatial profiles of local current density as electrons propagate from NM leads into the Floquet TI. For comparison, we also compute conductance of graphene-based realization of 2D quantum Hall, quantum anomalous Hall, and quantum spin Hall insulators. Although zero-temperature conductance within the gap of these three conventional time-independent 2D TIs of finite length exhibits small oscillations due to reflections at the NM-lead/2D-TI interface, it remains very close to perfectly quantized plateau at 2e 2 /h and completely insensitive to edge disorder. This is due to the fact that inside conventional TIs there is only edge local current density which circumvents any disorder. In contrast, in the case of Floquet TI both bulk and edge local current densities contribute equally to total current, which leads to longitudinal conductance below the expected quantized plateau that is further reduced by edge vacancies. We propose two experimental schemes to detect coexistence of bulk and edge current densities within Floquet TI: (i) drilling a nanopore in the interior of irradiated region of graphene will induce backscattering of bulk current density, thereby reducing longitudinal conductance by ∼28%; (ii) imaging of magnetic field produced by local current density using diamond nitrogen-vacancy centers.

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Failure of Conductance Quantization in Two-Dimensional Topological Insulators due to Nonmagnetic Impurities

Cited by 77 publications

References 57 publications

Conductance of quantum spin Hall edge states from first principles: The critical role of magnetic impurities and inter-edge scattering

Conductance of quantum spin Hall edge states from first principles: The critical role of magnetic impurities and inter-edge scattering

Cobalt-based magnetic Weyl semimetals with high-thermodynamic stabilities

Robustness of quantized transport through edge states of finite length: Imaging current density in Floquet topological versus quantum spin and anomalous Hall insulators

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