801 research outputs found
Optical conductivity of CuO_2 infinite-layer films
The infrared conductivity of CaCuO_2, SrCuO_{2-y}, and
Sr_{0.85}Nd_{0.15}CuO_2 infinite-layer films is obtained from reflectivity
measurements by taking into account the substrate contribution. SrCuO_{2-y} and
Sr_{0.85}Nd_{0.15}CuO_2 exhibit extra-phonon modes and structured bands in the
midinfrared, not found in stoichiometric CaCuO_2. These features mirror those
observed in the perovskitic cuprates, thus showing that the polaronic
properties of high-T_c superconductors are intrinsic to the CuO_2 planes.Comment: File latex, 5 p. incl. 4 fig. in epsf. Submitted to Solid State Com
Coherent optical binary polarisation shift keying heterodyne system in the free-space optical turbulence channel
In this paper, analytical and simulation results for the bit error rate (BER) performance and fading penalty of a coherent optical binary polarization shift keying (2PolSK) heterodyne system adopted for a free space optical (FSO) communication link modeled as the log-normal and the negative exponential atmospheric turbulence channels are presented. The conditional and unconditional BER expressions are derived, demonstrating the comprehensive similarity between the 2PolSK and the binary frequency shift keying (2FSK) schemes with regards to the system sensitivity. The power penalty due to the non-ideal polarization beam splitter (PBS) is also analyzed. The receiver sensitivity employing 2PolSK is compared with other modulation schemes in the presence of turbulence and the phase noise. The results show that 2PolSK offers improved signal-to-noise ratio (SNR) performance compared to the binary amplitude shift keying (2ASK)
Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La(2-x)Sr(x)CuO(4)
By using new and previous measurements of the -plane conductivity
of LaSrCuO (LSCO) it is shown that
the spectral weight
obeys the same law which holds for a conventional
metal like gold, for 's below the plasma frequency. However
, which measures the "thermal response" of the charge system, in
LSCO exhibits a peculiar behavior which points towards correlation effects. In
terms of hopping models, is directly related to an energy scale
, smaller by one order of magnitude than the full bandwidth .Comment: 4 pages with 3 fig
Reflectivity measurements in uniaxial superconductors: a methodological discussion applied to the case of La(2-x)Sr(x)CuO(4)
Most of the novel superconductors are uniaxial crystals, with metallic planes
() orthogonal to an insulating axis (). Far-infrared measurements of the
reflectivity provide valuable information on their low-energy
electrodynamics, but involve delicate experimental issues. Two of them are a
possible contamination of from the c axis and the
extrapolation of the data to =0, both above and below .
Here we discuss quantitatively these issues with particular regard to
LaSrCuO, one of the most studied high- materials.Comment: 13 pages with 3 Fig
Temperature dependence of the optical spectral weight in the cuprates: Role of electron correlations
We compare calculations based on the Dynamical Mean-Field Theory of the
Hubbard model with the infrared spectral weight of
LaSrCuO and other cuprates. Without using fitting parameters we
show that most of the anomalies found in with respect to normal
metals, including the existence of two different energy scales for the doping-
and the -dependence of , can be ascribed to strong correlation
effects.Comment: 4 pages, 3 figures. Minor corrections, corrected some typos and added
reference
Far-infrared absorption and the metal-to-insulator transition in hole-doped cuprates
By studying the optical conductivity of BSLCO and YCBCO, we show that the
metal-to-insulator transition (MIT) in these hole-doped cuprates is driven by
the opening of a small gap at low T in the far infrared. Its width is
consistent with the observations of Angle-Resolved Photoemission Spectroscopy
in other cuprates, along the nodal line of the k-space. The gap forms as the
Drude term turns into a far-infrared absorption, whose peak frequency can be
approximately predicted on the basis of a Mott-like transition. Another band in
the mid infrared softens with doping but is less sensitive to the MIT.Comment: To be published on Physical Review Letter
Phase diagram and optical conductivity of La1.8-xEu0.2SrxCuO4
La1.8-xEu0.2SrxCuO4 (LESCO) is the member of the 214 family which exhibits
the largest intervals among the structural, charge ordering (CO), magnetic, and
superconducting transition temperatures. By using new dc transport measurements
and data in the literature we construct the phase diagram of LESCO between x =
0.8 and 0.20. This phase diagram has been further probed in ac, by measuring
the optical conductivity {\sigma}1({\omega}) of three single crystals with x =
0.11, 0.125, and 0.16 between 10 and 300 K in order to associate the
extra-Drude peaks often observed in the 214 family with a given phase. The
far-infrared peak we detect in underdoped LESCO is the hardest among them,
survives up to room temperature and is associated with charge localization
rather than with ordering. At the CO transition for the commensurate doping x =
0.125 instead the extra-Drude peak hardens and a pseudogap opens in
{\sigma}1({\omega}), approximately as wide as the maximum superconducting gap
of LSCO.Comment: 6 pages, 6 figure
Effects of Superconductivity and Charge Order on the sub-Terahertz reflectivity of LaBaSrCuO
The reflectivity of both the plane and the c axis of two
single crystals of LaBaSrCuO has been measured
down to 5 cm, using coherent synchrotron radiation below 30 cm.
For = 0.085, a Josephson Plasma Resonance is detected at = 31 K
in , and a far-infrared peak (FIP) appears in the optical
conductivity below 50 K, where non-static charge ordering (CO) is reported by
X-ray scattering. For = 0.05 ( = 10 K), a FIP is observed in the
low-temperature tetragonal phase below the ordering temperature . At
1/8 doping the peak frequency scales linearly with , confirming that
the FIP is an infrared signature of CO, either static or fluctuating.Comment: v2: longer version, 9 pages, 6 color figure
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