6 research outputs found
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)
from the two-terminal value , 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 , we observe a finite
throughout the plateau. We identify the localized states as the cause of the
finite and propose a theoretical model which qualitatively
explains our findings.Comment: 26 pages 9 figure
Tunable Length and Optical Properties of CsPbX<sub>3</sub> (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 (CsPbBr<sub>3</sub>) 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<sup>+</sup> during crystallization. Therefore, the positions of the Cs<sup>+</sup> 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