860 research outputs found
A simple method for the Kramers-Kronig analysis of reflectance spectra measured with diamond anvil cell
When the optical reflectance spectrum of a sample under high pressure is
studied with a diamond anvil cell, it is measured at a sample/diamond
interface. Due to the large refractive index of diamond, the resulting
reflectance Rd(w) may substantially differ from that measured in vacuum. To
obtain optical constants from Rd(w), therefore, the usual Kramers-Kronig (KK)
transform cannot be straightforwardly applied, and either a spectral fitting or
a modified KK transform has been used. Here we describe an alternative method
to perform KK analysis on Rd(w). This method relies on the usual KK transform
with an appropriate cutoff and extrapolation to Rd(w), and may offer a simpler
approach to obtain infrared conductivity from measured Rd(w).Comment: 6 pages, 2 figures, to appear in the Proceedings of 6th WIRMS
Conference (J. Phys. Conf. Ser.
Optical evidence for a spin-filter effect in the charge transport of
We have measured the optical reflectivity of
as a function of temperature between 1.5 and 300
and in external magnetic fields up to 7 . The slope at the onset of the
plasma edge feature in increases with decreasing temperature and
increasing field but the plasma edge itself does not exhibit the remarkable
blue shift that is observed in the binary compound . The analysis of
the magnetic field dependence of the low temperature optical conductivity
spectrum confirms the previously observed exponential decrease of the
electrical resistivity upon increasing, field-induced bulk magnetization at
constant temperature. In addition, the individual exponential magnetization
dependences of the plasma frequency and scattering rate are extracted from the
optical data.Comment: submitted to Phys. Rev. Let
Magneto-optical evidence of double exchange in a percolating lattice
Substituting by in ferromagnetic leads to a percolation
limited magnetic ordering. We present and discuss magneto-optical data of the
series, based on measurements of the reflectivity
from the far infrared up to the ultraviolet, as a function of
temperature and magnetic field. Via the Kramers-Kronig transformation of
we extract the complete absorption spectra of samples with
different values of . The change of the spectral weight in the Drude
component by increasing the magnetic field agrees with a scenario based on the
double exchange model, and suggests a crossover from a ferromagnetic metal to a
ferromagnetic Anderson insulator upon increasing -content at low
temperatures.Comment: 10 pages, 3 figure
Neutral carbon in the Egg Nebula (AFGL 2688)
A search for sub-mm C I emission from seven stars that are surrounded by dense molecular gas shells led to the detection, in the case of the "Egg Nebula' (AFGL 2688), of an 0.9 K line implying a C I/CO value greater than 5. The material surrounding this star must be extremely carbon-rich, and it is suggested that the apparently greater extent of the C I emission region may be due to the effects of the galactic UV field on the shell's chemistry, as suggested by Huggins and Glassgold (1982)
Supermetallic conductivity in bromine-intercalated graphite
Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to
in-plane charge conductivities which increase monotonically with intercalation
time toward values (for ~6 at% Br) that are significantly higher than Cu at
temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic
susceptibility measurements confirm that the Br dopes the graphene sheets with
holes while simultaneously increasing the interplanar separation. The increase
of mobility (~ 5E4 cm^2/Vs at T=300 K) and resistance anisotropy together with
the reduced diamagnetic susceptibility of the intercalated samples suggests
that the observed supermetallic conductivity derives from a parallel
combination of weakly-coupled hole-doped graphene sheets.Comment: 5 pages, 4 figure
Pressure dependence of the single particle excitation in the charge-density-wave CeTe system
We present new data on the pressure dependence at 300 K of the optical
reflectivity of CeTe, which undergoes a charge-density-wave (CDW) phase
transition well above room temperature. The collected data cover an
unprecedented broad spectral range from the infrared up to the ultraviolet,
which allows a robust determination of the gap as well as of the fraction of
the Fermi surface affected by the formation of the CDW condensate. Upon
compressing the lattice there is a progressive closing of the gap inducing a
transfer of spectral weight from the gap feature into the Drude component. At
frequencies above the CDW gap we also identify a power-law behavior, consistent
with findings along the Te series (i.e., chemical pressure) and
suggestive of a Tomonaga-Luttinger liquid scenario at high energy scales. This
newest set of data is placed in the context of our previous investigations of
this class of materials and allows us to revisit important concepts for the
physics of CDW state in layered-like two-dimensional systems
Pressure dependence of the charge-density-wave gap in rare-earth tri-tellurides
We investigate the pressure dependence of the optical properties of CeTe,
which exhibits an incommensurate charge-density-wave (CDW) state already at 300
K. Our data are collected in the mid-infrared spectral range at room
temperature and at pressures between 0 and 9 GPa. The energy for the single
particle excitation across the CDW gap decreases upon increasing the applied
pressure, similarly to the chemical pressure by rare-earth substitution. The
broadening of the bands upon lattice compression removes the perfect nesting
condition of the Fermi surface and therefore diminishes the impact of the CDW
transition on the electronic properties of Te.Comment: 5 pages, 4 figure
Photogenerated Carriers in SrTiO3 Probed by Mid-Infrared Absorption
Infrared absorption spectra of SrTiO have been measured under
above-band-gap photoexcitations to study the properties of photogenerated
carriers, which should play important roles in previously reported photoinduced
phenomena in SrTiO. A broad absorption band appears over the entire
mid-infrared region under photoexcitation. Detailed energy, temperature, and
excitation power dependences of the photoinduced absorption are reported. This
photo-induced absorption is attributed to the intragap excitations of the
photogenerated carriers. The data show the existence of a high density of
in-gap states for the photocarriers, which extends over a wide energy range
starting from the conduction and valence band edges.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp
- …