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Register a new userInfrared signatures of hole and spin stripes in La{2-x}Sr{x}CuO{4}
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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.
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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.
We report a detailed inelastic neutron scattering study of the collective magnetic excitations of overdoped superconducting La1.78Sr0.22CuO4 for the energy range 0-160 meV. Our measurements show that overdoping suppresses the strong response present for optimally doped La2-xSrxCuO4 which is peaked near 50 meV. The remaining response is peaked at incommensurate wavevectors for all energies investigated. We observe a strong high-frequency magnetic response for E >= 80 meV suggesting that significant antiferromagnetic exchange couplings persist well into the overdoped part of the cuprate phase diagram.
Low energy spin excitations were investigated in the static stripe phase of La_{2-x}Sr_xCuO_4 using elastic and inelastic neutron scattering on single crystals. For x = 1/8 in which long-range static stripe order exists, an energy gap of E_g = 4 meV exists in the excitation spectrum in addition to strong quasi-elastic, incommensurate spin fluctuations associated with the static stripes. When x increases, the spectral weight of the spin fluctuations shifts from the quasi-elastic continuum to the excitation spectrum above E_g. The dynamic correlation length as a function of energy and the temperature evolution of the energy spectrum suggest a phase separation of two distinct magnetic phases in real space.
We demonstrate that one can measure the charge-stripe order parameter in the hole-doped CuO(2) planes of La(1.875)Ba(0.125)CuO(4), La(1.48)Nd(0.4)Sr(0.12)CuO(4) and La(1.68)Eu(0.2)Sr(0.12)CuO(4) utilizing the wipeout effects of Cu-63 NQR. Application of the same approach to La(2-x)Sr(x)CuO(4) reveals the presence of similar stripe order for the entire underdoped superconducting regime 1/16 < x < 1/8.
We present results of magnetic neutron diffraction experiments on the co-doped super-oxygenated La(2-x)Sr(x)CuO(4+y) (LSCO+O) system with x=0.09. The spin-density wave has been studied and we find long-range incommensurate antiferromagnetic order below T_N coinciding with the superconducting ordering temperature T_c=40 K. The incommensurability value is consistent with a hole-doping of n_h~1/8, but in contrast to non-superoxygenated La(2-x)Sr(x)CuO(4) with hole-doping close to n_h ~ 1/8 the magnetic order parameter is not field-dependent. We attribute this to the magnetic order being fully developed in LSCO+O as in the other striped lanthanum-cuprate systems.
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