We are as interested as the the commenters [1] about the possibility of observing a Dirac loop in a real physical system. In our work [2] we showed a simple class of lattice models that possess a Dirac loop at theier Fermi level and detailed some of the physical consequences of that loop, such as the possibility of a 3D anomalous Hall effect and topological surface states in the presence of spin-orbit coupling. nodal lines. It is remarkable that these loops can occur in simple hyper-honeycomb lattices.
The development of new methods to facilitate direct electron transfer (DET) between enzymes and electrodes is of much interest because of the desire for stable biofuel cells that produce significant amounts of power. In this study, hydroxylated multiwalled carbon nanotubes (MWCNTs) were covalently modified with anthracene groups to help orient the active sites of laccase to allow for DET. The onset of the catalytic oxygen reduction current for these biocathodes occurred near the potential of the T1 active site of laccase, and optimized biocathodes produced background-subtracted current densities up to 140 μA/cm 2 . Potentiostatic and galvanostatic stability measurements of the biocathodes revealed losses of 25% and 30%, respectively, after 24 h of constant operation. Finally, the novel biocathodes were utilized in biofuel cells employing two different anodic enzymes. A compartmentalized cell using a mediated glucose oxidase anode produced an open circuit voltage of 0.819 ( 0.022 V, a maximum power density of 56.8 ((1.8) μW/cm 2 , and a maximum current density of 205.7 ((7.8) μA/cm 2 . A compartment-less cell using a DET fructose dehydrogenase anode produced an open circuit voltage of 0.707 ( 0.005 V, a maximum power density of 34.4 ((2.7) μW/cm 2 , and a maximum current density of 201.7 ((14.4) μA/cm 2 .
We propose a family of structures that have "Dirac loops", closed lines of Dirac nodes in momentum space, on which the density of states vanishes linearly with energy. Those lattices all possess the planar trigonal connectivity present in graphene, but are three dimensional. We show that their highly anisotropic and multiply-connected Fermi surface leads to quantized Hall conductivities in three dimensions for magnetic fields with toroidal geometry. In the presence of spin-orbit coupling, we show that those structures have topological surface states. We discuss the feasibility of realizing the structures as new allotropes of carbon.Introduction.− In honeycomb lattices, the existence of the Dirac point results from the planar trigonal connectivity of the sites and its sub-lattice symmetry [1]. Less well known are "Dirac loops", three dimensional (3D) closed lines of Dirac nodes in momentum space, on which the energy vanishes linearly with the perpendicular components of momentum [2]. To date there are no experimental observations of Dirac loops, and they were predicted to exist only in topological superconductors [3] and 3D Dirac semimetals [4] in which the parameters such as interactions and magnetic field are finely tuned [2].Theoretically, graphene is not the only possible lattice realization with planar trigonally connected atoms [5]. It is therefore natural to ask if there are variations on the honeycomb geometry that might produce exotic Fermi surfaces with Dirac-like excitations and topologically non-trivial states. In this Letter, we propose a family of trigonally connected 3D lattices that admit simple tight-binding Hamiltonians having Dirac loops, without requiring any tuning or spin-orbit coupling. Some of these structures lie in the family of harmonic honeycomb lattices, which have been studied in the context of the Kitaev model [7][8][9][10][11], and experimentally realized in honeycomb iridates [12]. The simplest example is the hyper-honeycomb lattice, shown in Fig. 1a.We derive the low energy Hamiltonian of this family of systems, and analyze the quantization of the conductivity and possible surface states. Even though these systems are 3D semimetals, their Fermi surface is multiply connected, with the shape of a torus, and highly anisotropic. When a magnetic field with toroidal geometry is applied, we find that the Hall conductivity is quantized in 3D at sufficiently large field. Additional spin-orbit coupling effects can create topologically protected surface states in these crystals. We claim that in the presence of spin-orbit coupling, these structures conceptually correspond to a new family of strong 3D topological insulators [13,14]. We finally discuss the experimental feasibility of realizing those structures as new allotropic forms of carbon.Tight-binding lattice.− Our discussion starts with the simplest structure, the hyper-honeycomb lattice (see Fig.
Surfactant bilayers adsorbed on TS-1 zeolite were used as templates to produce colloidal nanocomposites with a polypyrrole (Ppy) shell. The adsorbed surfactant was cetylpyridinium chloride, and it plays a critical role for attaining both the colloidal stability of the nanocomposites and an enhanced conductivity of the Ppy sheath on the TS-1 core. The observed contact conductivity of the nanocomposites was 5 S/cm for a sample with 8 wt % of Ppy incorporation while bulk Ppy powder had a contact conductivity of 0.03 S/cm.
Ferrocene redox polymers based on the coupling of ferrocenecarboxaldehyde to both linear and branched poly(ethylenimine) (PEI) have been prepared to investigate the effects of pH, electrolyte, and cross-linking on electron charge transport and film swelling. The redox behavior of both ferrocene-modified linear PEI and ferrocene-modified branched PEI was investigated by cyclic voltammetry, while electron diffusion coefficients reported for PEI-based redox polymers were determined by electrochemical impedance spectroscopy. In phosphate solutions at pH>7, cross-linked films of both redox polymers exhibited multiple redox wave behavior and were unstable. In contrast, in non-phosphate solutions, cross-linked films exhibited stable electrochemical behavior and fast electron transfer in solutions with pH<11. Gel swelling experiments suggested that the multiple wave behavior and instability exhibited in either phosphate solutions or at high pH in non-phosphate solutions were related to a combination of film collapse and electrolyte binding within the hydrogel. The electron diffusion coefficients for these polymers are on the order of 10-8 (mol cm(-2) s(-1/2)), which are approximately 40 times greater than other ferrocene-modified polymers. Incorporation of the enzyme, glucose oxidase, into these films demonstrated that these redox polymers were able to electrically communicate with the enzyme's flavin adenine dinucleotide (FAD) redox centers. Glucose sensors based on these films exhibited enzyme saturation current densities that ranged from 240 to 480 microA/cm2 in response to glucose, which were dependent upon the supporting electrolyte and pH. The sensitivity of these sensors at 5 mM glucose ranged from 10 to 48 microA.cm(-2).mM(-1).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.