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

Abstract

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 wavefunctions, or infinite wires whose boundaries host surface or edge metallic states. 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 is particularly pressing issues 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 of Floquet TI using graphene irradiated by circularly polarized light did not exhibit either quantized longitudinal or Hall conductance. Here we employ charge conserving solution for Floquet-nonequlibrium Green functions (NEGFs) 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. 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 slightly 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 $\sim 28$%; (ii) imaging of magnetic field produced by local current density using diamond NV centers.

13 pages, 6 figures

References in corpus (15)

• Photovoltaic Hall effect in graphene
• Nonlocal edge state transport in the quantum spin Hall state
• Irradiated graphene as a tunable Floquet topological insulator
• Kondo effect in the helical edge liquid of the quantum spin Hall state
• Multiterminal Conductance of a Floquet Topological Insulator
• Effective Theory of Floquet Topological Transitions
• Microscopic theory for the light-induced anomalous Hall effect in graphene
• Imaging mesoscopic spin Hall flow: Spatial distribution of local spin currents and spin densities in and out of multiterminal spin-orbit coupled semiconductor nanostructures
• Effect of radiation on transport in graphene
• Conductance of a helical edge liquid coupled to a magnetic impurity
• Conductivity of a generic helical liquid
• Edge currents shunt the insulating bulk in gapped graphene
• Giant thermoelectric effect in graphene-based topological insulators with nanopores
• A computational study of two-terminal transport of Floquet quantum Hall insulators
• Charge, Spin and Valley Hall Effects in Disordered Graphene

Cited by in corpus (7)

• Spin-polarized tunable photocurrents
• High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin-orbit coupling
• Quantum Hall edge states under periodic driving: a Floquet induced chirality switch
• Flow-equation approach to quantum systems driven by an amplitude-modulated time-periodic force
• Time-reversal invariant topological skyrmion phases
• Suppression of scattering from slow to fast subsystems and application to resonantly Floquet-driven impurities in strongly interacting systems
• Floquet-Engineered Valley-Topotronics in Kekulé-Y Bond Textured Graphene Superlattice