1,174 research outputs found
Universal linear and nonlinear electrodynamics of the Dirac fluid
A general relation is derived between the linear and second-order nonlinear
ac conductivities of an electron system in the hydrodynamic regime of
frequencies below the interparticle scattering rate. The magnitude and
tensorial structure of the hydrodynamic nonlinear conductivity are shown to
differ from their counterparts in the more familiar kinetic regime of higher
frequencies. Due to universality of the hydrodynamic equations, the obtained
formulas are valid for systems with an arbitrary Dirac-like dispersion, ranging
from solid-state electron gases to free-space plasmas, either massive or
massless, at any temperature, chemical potential or space dimension.
Predictions for photon drag and second-harmonic generation in graphene are
presented as one application of this theory.Comment: 5 pages, 4 figure
Topological insulators are tunable waveguides for hyperbolic polaritons
Layered topological insulators, for example, BiSe are optically
hyperbolic materials in a range of THz frequencies. Such materials possess
deeply subdiffractional, highly directional collective modes: hyperbolic
phonon-polaritons. In thin crystals the dispersion of such modes is split into
discrete subbands and is strongly influenced by electron surface states. If the
surface states are doped, then hybrid collective modes result from coupling of
the phonon-polaritons with surface plasmons. The strength of the hybridization
can be controlled by an external gate that varies the chemical potential of the
surface states. Momentum-dependence of the plasmon-phonon coupling leads to a
polaritonic analog of the Goos-H\"anchen effect. Directionality of the
polaritonic rays and their tunable Goos-H\"anchen shift are observable via THz
nanoimaging.Comment: 12 pages, 7 figure
Interplane charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors
We present calculations of the interplane charge dynamics in the normal state
of cuprate superconductors within the valence-bond dynamical mean-field theory.
We show that by varying the hole doping, the c-axis optical conductivity and
resistivity dramatically change character, going from metallic-like at large
doping to insulating-like at low-doping. We establish a clear connection
between the behavior of the c-axis optical and transport properties and the
destruction of coherent quasiparticles as the pseudogap opens in the antinodal
region of the Brillouin zone at low doping. We show that our results are in
good agreement with spectroscopic and optical experiments.Comment: 5 pages, 3 figure
Charge dynamics in the half-metallic ferromagnet CrO\u3csub\u3e2\u3c/sub\u3e
Infrared spectroscopy is used to investigate the electronic structure and charge carrier relaxation in crystalline films of CrO2 which is the simplest of all half-metallic ferromagnets. Chromium dioxide is a bad metal at room temperature but it has a remarkably low residual resistivity (\u3c5 \u3eμΩ cm) despite the small spectral weight associated with free carrier absorption. The infrared measurements show that low residual resistivity is due to the collapse of the scattering rate at ω\u3c2000 \u3ecm-1. The blocking of the relaxation channels at low v and T can be attributed to the unique electronic structure of a half-metallic ferromagnet. In contrast to other ferromagnetic oxides, the intraband spectral weight is constant below the Curie temperature
Plasmonic Hot Spots in Triangular Tapered Graphene Microcrystals
Recently, plasmons in graphene have been observed experimentally using
scattering scanning near-field optical microscopy. In this paper, we develop a
simplified analytical approach to describe the behavior in triangular samples.
Replacing Coulomb interaction by a short-range one reduces the problem to a
Helmholtz equation, amenable to analytical treatment. We demonstrate that even
with our simplifications, the system still exhibits the key features seen in
the experiment.Comment: 4 pages, 3 figure
Colloquium: Graphene spectroscopy
Spectroscopic studies of electronic phenomena in graphene are reviewed. A
variety of methods and techniques are surveyed, from quasiparticle
spectroscopies (tunneling, photoemission) to methods probing density and
current response (infrared optics, Raman) to scanning probe nanoscopy and
ultrafast pump-probe experiments. Vast complimentary information derived from
these investigations is shown to highlight unusual properties of Dirac
quasiparticles and many-body interaction effects in the physics of graphene.Comment: 36 pages, 16 figure
Asymptotically self-similar propagation of the spherical ionization waves
It is shown that a new type of the self-similar spherical ionization waves
may exist in gases. All spatial scales and the propagation velocity of such
waves increase exponentially in time. Conditions for existence of these waves
are established, their structure is described and approximate analytical
relationships between the principal parameters are obtained. It is notable that
spherical ionization waves can serve as the simplest, but structurally complete
and physically transparent model of streamer in homogeneous electric field.Comment: Corrected typos, the more precise formulas are obtaine
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