Heat Conductance of the Quantum Hall Bulk

The Quantum Hall Effect (QHE) is the prototypical realization of a topological state of matter. It emerges from a subtle interplay between topology, interactions, and disorder. The disorder enables the formation of localized states in the bulk that stabilize the quantum Hall states with respect to the magnetic field and carrier density. Still, the details of the localized states and their contribution to transport remain beyond the reach of most experimental techniques. Here, we describe an extensive study of the bulk's heat conductance. Using a novel 'multi-terminal' device, we separate the longitudinal thermal conductance (due to bulk's contribution) $\kappa_{xx}T$ from the two-terminal value $\kappa_{2T}T$, by eliminating the contribution of the edge modes. We find that when the field is tuned away from the conductance plateau center, the electronic states of the bulk conduct heat efficiently while the bulk remains electrically insulating. For fragile fractional states, such as the non-Abelian $\nu=5/2$, we observe a finite $\kappa_{xx}T$ throughout the plateau. We identify the localized states as the cause of the finite $\kappa_{xx}T$ and propose a theoretical model which qualitatively explains our findings.Comment: 26 pages 9 figure

Tunable Length and Optical Properties of CsPbX₃ (X = Cl, Br, I) Nanowires with a Few Unit Cells

Perovskite nanostructures, both hybrid organo–metal and fully inorganic perovskites, have gained a lot of interest in the past few years for their intriguing optical properties in the visible region. We report on inorganic cesium lead bromide (CsPbBr₃) nanowires (NWs) having quantum confined dimensions corresponding to 5 unit cells. The addition of various hydrohalic acids (HX, X = Cl, Br, I) was found to highly affect the NW length, composition, and optical properties. Hydrochloric (HCl) and hydroiodic (HI) acids mixed in the reaction solution influence the crystal structure and optical properties and shorten the NWs, while the hydrobromic acid (HBr) addition results solely in shorter NWs, without any structural change. The addition of HX increases the acidity of the reaction solution, resulting in protonation of the oleylamine ligands from oleylamine into oleyl-ammonium cations that behave similarly to Cs⁺ during crystallization. Therefore, the positions of the Cs⁺ at the growing surface of the NWs are taken by the oleyl-ammonium cations, thus blocking further growth in the favored direction. The emission of the NWs is tunable between ∼423–505 nm and possesses a potential in the optoelectronic field. Moreover, electrical conductivity measurements of the NWs are discussed to give a new point of view regarding the conductivity of perovskite nanostructures

Integrating DNA with Functional Nanomaterials

DNA may be the most versatile molecule discovered to date. Beyond its well-known central role in genetics, DNA has the potential to be a remarkably useful technological material. It has been demonstrated as a scaffold for the assembly of organic and inorganic nanomaterials [1]; a vehicle for drug delivery [2]; a medium for computation [3]; and a possible wire for transporting electrical signals [4]. A key factor in exploiting DNA in these ways is the ability to integrate DNA with other materials. In this paper, we review two approaches to forming DNA complexes with functional nanomaterials: (1) linking DNA with single-wall carbon nanotubes (SWCNTs), which can then be used as nanoscale electrical contacts for probing electron transport in DNA; and (2) directed nanoassembly of Au nanoparticles using DNA/PNA (peptide nucleic acid) hybrid scaffolds

Conductivity Enhancement of Transparent 2D Carbon Nanotube Networks Occurs by Resistance Reduction in All Junctions

Transparent conductive networks are important for flexible electronics and solar cells. Often interwire (junction) conductivity is the limiting factor for network conductivity and can be improved by various treatments. The conductivity of individual junctions in a single walled carbon nanotube network was measured by conductive atomic force microscopy before and after exposure to nitric acid. The measurements show that this exposure improves the conductivity of each one of the junctions within the network. Our results suggest that the acid improves the conductivity by p-type charge transfer doping and by surfactant degradation

Long-range charge transport in single G-quadruplex DNA molecules

DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100 pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100 nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits