1,529 research outputs found
The phase plane of moving discrete breathers
We study anharmonic localization in a periodic five atom chain with
quadratic-quartic spring potential. We use discrete symmetries to eliminate the
degeneracies of the harmonic chain and easily find periodic orbits. We apply
linear stability analysis to measure the frequency of phonon-like disturbances
in the presence of breathers and to analyze the instabilities of breathers. We
visualize the phase plane of breather motion directly and develop a technique
for exciting pinned and moving breathers. We observe long-lived breathers that
move chaotically and a global transition to chaos that prevents forming moving
breathers at high energies.Comment: 8 pages text, 4 figures, submitted to Physical Review Letters. See
http://www.msc.cornell.edu/~houle/localization
Through a Lattice Darkly -- Shedding Light on Electron-Phonon Coupling in the High T Cuprates
With its central role in conventional BCS superconductivity, electron-phonon
coupling has appeared to play a more subtle role in the phase diagram of the
high temperature superconducting cuprates. The added complexity of the cuprates
with potentially numerous competing phases including charge, spin, orbital, and
lattice ordering, makes teasing out any unique phenomena challenging. In this
review, we present our work using angle resolved photoemission spectroscopy
(ARPES) to explore the role of the lattice and its effect on the valence band
electronic structure in the cuprates. We provide an introduction to the ARPES
technique and its unique ability to the probe the effect of bosonic
renormalization (or "kink") on the near-E band structure. Our survey begins
with the establishment of the ubiquitous nodal cuprate kink leading to the way
isotope substitution has shed a critical new perspective on the role and
strength of electron-phonon coupling. We continue with recently published work
on the connection between the phonon dispersion as seen with inelastic x-ray
scattering (IXS) and the location of the kink as observed by ARPES near the
nodal point. Finally, we present very recent and ongoing ARPES work examining
how induced strain through chemical pressure provides a potentially promising
avenue for understanding the broader role of the lattice to the superconducting
phase and larger cuprate phase diagram.Comment: 17 pages, 20 figures, Review Articl
Visualizing Poiseuille flow of hydrodynamic electrons
Hydrodynamics is a general description for the flow of a fluid, and is
expected to hold even for fundamental particles such as electrons when
inter-particle interactions dominate. While various aspects of electron
hydrodynamics were revealed in recent experiments, the fundamental spatial
structure of hydrodynamic electrons, the Poiseuille flow profile, has remained
elusive. In this work, we provide the first real-space imaging of Poiseuille
flow of an electronic fluid, as well as visualization of its evolution from
ballistic flow. Utilizing a scanning nanotube single electron transistor, we
image the Hall voltage of electronic flow through channels of high-mobility
graphene. We find that the profile of the Hall field across the channel is a
key physical quantity for distinguishing ballistic from hydrodynamic flow. We
image the transition from flat, ballistic field profiles at low temperature
into parabolic field profiles at elevated temperatures, which is the hallmark
of Poiseuille flow. The curvature of the imaged profiles is qualitatively
reproduced by Boltzmann calculations, which allow us to create a 'phase
diagram' that characterizes the electron flow regimes. Our results provide
long-sought, direct confirmation of Poiseuille flow in the solid state, and
enable a new approach for exploring the rich physics of interacting electrons
in real space
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