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Register a new userInfrared signatures of charge stripes in La(2-x)Sr(x)CuO(4)
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The in-plane optical conductivity of seven La(2-x)Sr(x)CuO(4) single crystals with x between 0 and 0.15 has been studied from 30 to 295 K. All doped samples exhibit strong peaks in the far-infrared, which closely resemble those observed in Cu-O ladders with one-dimensional charge-ordering. The behavior with doping and temperature of the peak energy, width, and intensity allows us to conclude that we are observing charge stripes dynamics in La(2-x)Sr(x)CuO(4) on the fast time scale of infrared spectroscopy.
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We investigate the hole and lattice dynamics in a prototypical high temperature superconducting system La{2-x}Sr{x}CuO{4} using infrared spectroscopy. By exploring the anisotropy in the electronic response of CuO2 planes we show that our results support the notion of stripes. Nevertheless, charge ordering effects are not apparent in the phonon spectra. All crystals show only the expected infrared active modes for orthorhombic phases without evidence for additional peaks that may be indicative of static charge ordering. Strong electron-phonon interaction manifests itself through the Fano lineshape of several phonon modes. This analysis reveals anisotropic electron-phonon coupling across the phase diagram, including superconducting crystals. Due to the ubiquity of the CuO2 plane, these results may have implications for other high Tc superconductors.
The superconducting properties of high-tc materials are functions of carriers concentration, which is controlled by the concentration of defects including heterovalent cations, interstitial oxygen ions, and oxygen vacancies. Here we combine low-temperature thermal treatment of La$_{2-x}$Sr$_{x}$CuO$_{4}$ epitaxial thin films and confocal Raman spectroscopy to control and investigate oxygen vacancies. We demonstrate that the apical site is the most favorable position to accommodate oxygen vacancies under low-temperature annealing conditions. Additionally we show that in high-quality films of overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$, oxygen vacancies strongly deform the oxygen environment around the copper ions. This observation is consistent with previous defect-chemical studies, and calls for further investigation of the defect induced properties in the overdoped regime of the hole-doped lanthanum cuprates.
Magnetic excitations in the energy range up to 100 meV are studied for over-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ with $x=0.25$ and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, $20 lesssim omega lesssim 100$ meV, progressively decreases with over-doping. This strongly suggests that the magnetism is not related to Fermi surface nesting, but rather is associated with a decreasing volume fraction of (probably fluctuating) antiferromagnetic bubbles.
We have measured out-of-plane resistivity $rho_c$ for La$_{2-x}$Sr$_{x}$CuO$_{4}$ under anisotropic pressure. c-axis compression, which decreases $rho_c$, reduces $T_{rm c}$ drastically, whereas c-axis extention, which increases $rho_c$, enhances $T_{rm c}$ from 38K at ambient pressure to 51.6K at 8GPa. We find that the variation of $T_{rm c}$ scales as a function of $rho_c$, and that the c-axis pressure coefficient is much stronger than the ab-axis one. These imply that $T_{rm c}$ depends primarily on the interlayer, rather than the in-plane, lattice parameter.
By using new and previous measurements of the $ab$-plane conductivity $sigma_1^{ab} (omega,T)$ of La$_{2-x}$Sr$_x$CuO$_{4}$ (LSCO) it is shown that the spectral weight $W = int_0^Omega {sigma_1^{ab} (omega,T) domega}$ obeys the same law $W = W_0 - B(Omega) T^2$ which holds for a conventional metal like gold, for $Omega$s below the plasma frequency. However $B(Omega)$, 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, $B(Omega)$ is directly related to an energy scale $t_T$, smaller by one order of magnitude than the full bandwidth $t_0 sim W_0$.
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