Lattice effects in the La 2− x Sr x CuO 4 compounds (original) (raw)
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Lattice effects in the La$_{\rm 2-x}$Sr$_{\rm x}$CuO$_{\rm 4}$ compounds
2009
Systematic Raman studies on several cuprates (YBa 2 Cu 3 O x , YBa 2 Cu 4 O 8 or Bi 2 Sr 2 CaCu 2 O 8 ) have shown that at optimal doping the compounds are at the edge of lattice instability; once this level is exceeded, by means of doping or applying external hydrostatic pressure, the changes in the transition temperature are accompanied by spectral modifications. There are strong indications that the reduction in T c is correlated with a separation into nanoscale phases, which involve the oxygen atoms of the CuO 2 planes. In this work, modifications with doping in the Raman spectra of the La 2−x Sr x CuO 4 compound are presented, which show that spin or charge ordering is coupled with lattice distortions in the whole doping region.
A Raman view of local lattice distortions and charge transfer in cuprates
Journal of Physics and Chemistry of Solids, 2006
Small changes in doping or the application of a hydrostatic pressure can induce non-linear lattice distortions, lattice instabilities, and phase separation in the cuprates. In YBa 2 Cu 3 O x , oxygen doping above optimal induces a separation into microphases originating from a modification in the buckling of the CuO 2 planes. In the same compound, the excess nominal doping by Ca creates changes in the CuO 2 buckling at some critical concentrations. These are correlated with the formation of domains where the additional carriers brought by Ca remain isolated surrounded by yttrium atoms. Furthermore, it was observed that hydrostatic pressure induces non-linear modifications in the spectral characteristics of the A g-symmetry phonons in all cuprates studied (YBa 2 Cu 3 O 6.5 , YBa 2 Cu 3 O over , YBa 2 Cu 4 O 8 , and Bi 2 Sr 2 CaCu 2 O 8). A coexistence of phases appears at a critical pressure where changes in the superconducting transition temperature have been detected. We have also observed similar correlations between the transition temperature and spectral modifications by chemical doping in the Raman spectra of La 2Àx Sr x CuO 4. Finally, soft modes were found in the cuprates studied, with energies scaling with the maximum transition temperature of the compound.
Journal of Physics: Condensed Matter, 2007
We have performed a systematic angle-resolved photoemission spectroscopy (ARPES) study of the high-T c cuprates La 2−x Sr x CuO 4 , ranging from the underdoped insulator to the superconductor to the overdoped metal. We have revealed a systematic doping evolution of the band dispersions and (underlying) Fermi surfaces, pseudogap and quasi-particle features under the influence of strong electron-electron interaction and electron-phonon interaction. The unusual transport and thermodynamic properties are explained by taking into account the pseudogap opening and the Fermi arc formation, due to which the carrier number decreases as the doped hole concentration decreases.
Physical Review B, 2011
We discuss the problem of the glue mediating the effective electron-electron interaction and the related order underlying superconductivity in the cuprates. Assuming as mediators spin and charge fluctuations with different characteristic wavevectors, we calculate the Raman response function including self-energy and vertex corrections. In this way, exploiting the related cancellations, we are able to individuate the charge and spin contributions in the Raman response function. Raman scattering experiments in La 2−x Sr x CuO 4 single crystals have been systematically carried out at various doping levels x. By fitting the experimental spectra within the above theoretical framework, we find a charge and spin nearly ordered state, whose fluctuations give rise to a spin dominated glue function at intermediate doping and a charge dominated one above optimal doping.
Phase separation and the dual nature of the electronic structure of the La 2− x Sr x CuO 4
Physica C-superconductivity and Its Applications, 2007
The dual nature of the electronic structure of stripes in La2−xSrxCuO4 was characterized by many experiments. We present here an attempt to characterize this dual behavior based on the Cahn-Hilliard theory of a phase separation transition which is assumed to occur at the high pseudogap temperature. The resulting inhomogeneous low doping system is formed of hole-rich (metallic like) regions embedded in a hole-poor (insulator like). This inhomogeneous configuration is analyzed by a new method within the Bogoliubov-deGennes superconducting theory. This approach describes well the electronic nodal-antinodal dichotomy and parts of the phase diagram.
Physical Review Letters, 2002
We present measurements of the magnetic penetration depth, \lambda^{-2}(T), in Pr_{2-x}Ce_{x}CuO_{4-y} and La_{2-x}Ce_{x}CuO_{4-y} films at three Ce doping levels, x, near optimal. Optimal and overdoped films are qualitatively and quantitatively different from underdoped films. For example, \lambda^{-2}(0) decreases rapidly with underdoping but is roughly constant above optimal doping. Also, \lambda^{-2}(T) at low T is exponential at optimal and overdoping but is quadratic at underdoping. In light of other studies that suggest both d- and s-wave pairing symmetry in nominally optimally doped samples, our results are evidence for a transition from d- to s-wave pairing near optimal doping.
Dual Nature of the Electronic Structure of (La2-x-yNdySrx)CuO4 and La1.85Sr0.15CuO4
Physical Review Letters, 2001
High resolution angle−resolved photoemission measurements have been carried out on (La1.4−xNd0.6Srx)CuO4, a model system with static stripes, and (La1.85Sr0.15)CuO4, a high temperature superconductor (Tc=40K) with dynamic stripes. In addition to the straight segments near (π, 0) and (0, π) antinodal regions, we have identified the existence of nodal spectral weight and its associated Fermi surface in the electronic structure of both systems. The ARPES spectra in the nodal region show well−defined Fermi cut-off, indicating a metallic character of this charge−ordered state. This observation of nodal spectral weight, together with the straight segments near antinodal regions, reveals dual nature of the electronic structure of stripes due to the competition of order and disorder.