54 research outputs found
Wigner crystallization in Na(3)Cu(2)O(4) and Na(8)Cu(5)O(10) chain compounds
We report the synthesis of novel edge-sharing chain systems Na(3)Cu(2)O(4)
and Na(8)Cu(5)O(10), which form insulating states with commensurate charge
order. We identify these systems as one-dimensional Wigner lattices, where the
charge order is determined by long-range Coulomb interaction and the number of
holes in the d-shell of Cu. Our interpretation is supported by X-ray structure
data as well as by an analysis of magnetic susceptibility and specific heat
data. Remarkably, due to large second neighbor Cu-Cu hopping, these systems
allow for a distinction between the (classical) Wigner lattice and the 4k_F
charge-density wave of quantum mechanical origin.Comment: 4 pages, 4 figure
Bose-Fermi Mixtures in One Dimension
We analyze the phase stability and the response of a mixture of bosons and
spin-polarized fermions in one dimension (1D). Unlike in 3D, phase separation
happens for low fermion densities. The dynamics of the mixture at low energy is
independent of the spin-statistics of the components, and zero-sound-like modes
exist that are essentially undamped.Comment: 5 pages; 1 figur
Frequency- and electric-field-dependent conductivity of single-walled carbon nanotube networks of varying density
We present measurements of the frequency and electric field dependent
conductivity of single walled carbon nanotube(SWCNT) networks of various
densities. The ac conductivity as a function of frequency is consistent with
the extended pair approximation model and increases with frequency above an
onset frequency which varies over seven decades with a range of film
thickness from sub-monolayer to 200 nm. The nonlinear electric field-dependent
DC conductivity shows strong dependence on film thickness as well. Measurement
of the electric field dependence of the resistance R(E) allows for the
determination of a length scale possibly characterizing the distance
between tube contacts, which is found to systematically decrease with
increasing film thickness. The onset frequency of ac conductivity
and the length scale of SWCNT networks are found to be correlated, and
a physically reasonable empirical formula relating them has been proposed. Such
studies will help the understanding of transport properties and benefit the
applications of this material system.Comment: 7 pages and 6 figure
Holographic Charge Density Waves
We discuss a gravity dual of a charge density wave consisting of a U(1) gauge
field and two scalar fields in the background of an AdS Schwarzschild black
hole together with an antisymmetric field (probe limit). Interactions drive the
system to a phase transition below a critical temperature. We numerically
compute the ground states characterized by modulated solutions for the gauge
potential corresponding to a dynamically generated unidirectional charge
density wave in the conformal field theory. Signatures of the holographic
density waves are retrieved by studying the dynamical response to an external
electric field. We find that this novel holographic state shares many common
features with the standard condensed matter version of charge density wave
systems.Comment: 5 pages, 2 figures; improved discussion, published versio
Field- and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3
We studied the electrodynamic response of α-(BEDT-TTF)2I3 in a wide range of frequency, covering microwave and millimeter wave frequencies as well as the optical spectral range, and found a frequency dependent conductivity up to 1000 cm-1 in the low temperature phase. This is accompanied be a non-linear transport with a smooth onset at about 10 V /cm. Our X-ray studies show no indication of superstructure reflections and clearly rule out the formation of a charge density wave ground state. The lack of a temperature dependence in the millimeter wave conductivity between 20 K and 100 K makes hopping transport unlikely
Measurements of the Complex Conductivity of NbxSi1-x Alloys on the Insulating Side of the Metal-Insulator Transition
We have conducted temperature and frequency dependent transport measurements
in amorphous Nb_x Si_{1-x} samples in the insulating regime. We find a
temperature dependent dc conductivity consistent with variable range hopping in
a Coulomb glass. The frequency dependent response in the millimeter-wave
frequency range can be described by the expression with the exponent somewhat smaller than one. Our ac
results are not consistent with extant theories for the hopping transport.Comment: 4 pages with 3 figures; published version has a different title from
original (was: "Electrodynamics in a Coulomb glass"
Nanonet as a scaffold with targeted functionalities
A random assembly of nanoscale electrically conducting wires, a so called a nanonet, has a variety of interesting properties, which has been exploited for multiple applications. These nanowire networks can also be regarded as a “scaffold” onto which molecules and nanoscale objects can be attached for well defined functionalities. This review summarizes the strategies of the attachments onto the scaffold, the investigation of the interface between the scaffold and the functional species together with the applications in the areas of renewable energy, opto-electronics, catalysis and biotechnology. The initial work on this novel materials platform will likely followed up by development efforts so that the fundamental value propositions associated with the scaffold can be fully exploited. Initial work towards this goal is gradually emerging
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