3,464 research outputs found
Transport phenomenology for a holon-spinon fluid
We propose that the normal-state transport in the cuprate superconductors can
be understood in terms of a two-fluid model of spinons and holons. In our
scenario, the resistivity is determined by the properties of the holons while
magnetotransport involves the recombination of holons and spinons to form
physical electrons. Our model implies that the Hall transport time is a measure
of the electron lifetime, which is shorter than the longitudinal transport
time. This agrees with our analysis of the normal-state data. We predict a
strong increase in linewidth with increasing temperature in photoemission. Our
model also suggests that the AC Hall effect is controlled by the transport
time.Comment: 4 pages, 1 postscript figure. Uses RevTeX, epsf, multico
Infrared Hall conductivity of NaCoO
We report infrared Hall conductivity of
NaCoO thin films determined from Faraday rotation angle
measurements. exhibits two types of hole
conduction, Drude and incoherent carriers. The coherent Drude carrier shows a
large renormalized mass and Fermi liquid-like behavior of Hall scattering rate,
. The spectral weight is suppressed and disappears at T
= 120K. The incoherent carrier response is centered at mid-IR frequency and
shifts to lower energy with increasing T. Infrared Hall constant is positive
and almost independent of temperature in sharp contrast with the dc-Hall
constant.Comment: 5 Pages, 5 Figures. Author list corrected in metadata only, paper is
unchange
Measurement of the Far Infrared Magneto-Conductivity Tensor of Superconducting YBaCuO Thin Films
We report measurements of the far infrared transmission of superconducting
YBaCuO thin films from 5 cm to 200 cm in
fields up to 14. A Kramers-Kronig analysis of the magneto-transmission
spectrum yields the magneto-conductivity tensor. The result shows that the
magneto-conductivity of YBaCuO is dominated by three
terms: a London term, a low frequency Lorentzian ( 3 cm) of width 10 cm and a finite frequency Lorentzian of
width 17 cm at 24 cm in the hole
cyclotron resonance active mode of circular polarization.\\Comment: Revised LaTex file (12 pages) + 4 Postscript figures, uuencoded. In
response to referees' comments, we refined the paper a lot; we encourage you
to download this revised versio
Disentangling the exchange coupling of entangled donors in the Si quantum computer architecture
We develop a theory for micro-Raman scattering by single and coupled
two-donor states in silicon. We find the Raman spectra to have significant
dependence on the donor exchange splitting and the relative spatial positions
of the two donor sites. In particular, we establish a strong correlation
between the temperature dependence of the Raman peak intensity and the
interdonor exchange coupling. Micro-Raman scattering can therefore potentially
become a powerful tool to measure interqubit coupling in the development of a
Si quantum computer architecture.Comment: Title changed. Other minor change
Temperature dependent optical studies of TiCoO
We present the results of Raman and photoluminescence (PL) studies on
epitaxial anatase phase TiCoO films for = 0-0.07, grown by
pulsed laser deposition. The low doped system (=0.01 and 0.02) shows a Curie
temperature of ~700 K in the as-grown state. The Raman spectra from the doped
and undoped films confirm their anatase phase. The photoluminescence spectrum
is characterized by a broad emission from self-trapped excitons (STE) at 2.3 eV
at temperatures below 120 K. This peak is characteristic of the anatase-phase
TiO and shows a small blueshift with increasing doping concentration. In
addition to the emission from STE, the Co-doped samples show two emission lines
at 2.77 eV and 2.94 eV that are absent in the undoped film indicative of a
spin-flip energy.Comment: 8 pages, 4 figure
Mid-infrared Hall effect in thin-film metals: Probing the Fermi surface anisotropy in Au and Cu
A sensitive mid-infrared (MIR, 900-1100 cm-1, 112-136 meV) photo-elastic
polarization modulation technique is used to measure simultaneously Faraday
rotation and circular dichroism in thin metal films. These two quantities
determine the complex AC Hall conductivity. This novel technique is applied to
study Au and Cu thin films at temperatures down to 20 K and magnetic fields up
to 8 T. The Hall frequency is consistent with band theory predictions. We
report the first measurement of the MIR Hall scattering rate, which is
significantly lower than that derived from Drude analysis of zero magnetic
field MIR transmission measurements. This difference is qualitatively explained
in terms of the anisotropy of the Fermi surface in Au and Cu.Comment: 14 pages of text, 5 figure
Composite vortex model of the electrodynamics of high- superconductor
We propose a phenomenological model of vortex dynamics in which the vortex is
taken as a composite object made of two components: the vortex current which is
massless and driven by the Lorentz force, and the vortex core which is massive
and driven by the Magnus force. By combining the characteristics of the
Gittleman-Rosenblum model (Phys. Rev. Lett. {\bf 16}, 734 (1966)) and Hsu's
theory of vortex dynamics (Physica {\bf C 213},305 (1993)), the model provides
a good description of recent far infrared measurements of the
magneto-conductivity tensor of superconducting YBaCuO
films from 5 cm to 200 cm.Comment: LaTex file (12 pages) + 3 Postscript figures, uuencoded. More
information on this paper, please check
http://www.wam.umd.edu/~lihn/newmodel
Grain Boundary Induced Magneto-Far Infrared Resonances in Superconducting YBaCuO Thin Films
Spectral features induced by 45 in-plane misoriented grains have
been observed in the far infrared magneto-transmission of YBaCuO thin films. Two strong dispersive features are found at 80 and
160 and a weaker one at 116 . The data can be well
represented by Lorentzian oscillator contributions to the conductivity. Several
possible interpretations are discussed. We conclude that the resonances are due
to vortex core excitations.Comment: Latex file (14 pages) + 4 Postscript figures, uuencode
Magnetoresistance of YBa2Cu3O7 in the "cold spots" model
We calculate the in-plane magnetoresistance of
YBaCuO in a magnetic field applied perpendicular to the
planes for the ``cold spots'' model. In this model, the electron relaxation
time at small regions on the Fermi surface near the
Brillouin zone diagonals is much longer than the relaxation time
at the rest of the Fermi surface ( is temperature). In
qualitative agreement with the experiment, we find that Kohler's rule is
strongly violated, but the ratio ,
where is the Hall angle, is approximately
temperature-independent. We find the ratio is about 5.5, which is of the same
order of magnitude as in the experiment.Comment: RevTeX, 4 pages, 6 figures. V.2: 2 references adde
Normal State Spin Dynamics of Five-band Model for Iron-pnictides
Normal state spin dynamics of the recently discovered iron-pnictide
superconductors is discussed by calculating spin structure factor S(q, omega)
in an itinerant five-band model within RPA approximation. Due to the
characteristic Fermi surface structure of iron-pnictide, column like response
is found at (pi, 0) in extended Brillouin zone in the undoped case, which is
consistent with the recent neutron scattering experiment. This indicates that
the localized spin model is not necessary to explain the spin dynamics of this
system. Furthermore, we show that the temperature dependence of inelastic
neutron scattering intensity can be well reproduced in the itinerant model. We
also study NMR 1/T_1T in the same footing calculation and show that the
itinerant model can capture the magnetic property of iron-pnictide
superconductors.Comment: 4 page
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