Electronic structure ofLa2−xSrxCuO

Abstract

We report on the result of angle-resolved photoemission (ARPES) study of La2−xSrxCuO4 (LSCO) from an optimally doped superconductor (x = 0.15) to an antiferromagnetic insulator (x = 0). Near the superconductor-insulator transition (SIT) x ∼ 0.05, spectral weight is transferred with hole doping between two coexisting components, suggesting a microscopic inhomogeneity of the dopedhole distribution. For the underdoped LSCO (x ≤ 0.12), the dispersive band crossing the Fermi level becomes invisible in the (0, 0)−(π, π) direction unlike Bi2Sr2CaCu2O8+y. These observations may be reconciled with the evolution of holes in the insulator into fluctuating stripes in the superconductor.PACS numbers: 74.25.Jb, 71.30.+h, 74.72.Dn, 74.62.Dh The key issue to clarify the nature of high-temperature superconductivity in the cuprates is how the electronic structure evolves from the antiferromagnetic insulator (AFI) to the superconductor (SC) with hole doping. For the hole-doped CuO 2 planes in the superconductors, band dispersions and Fermi surfaces have been extensively studied by angle-resolved photoemission spectroscopy (ARPES) primarily on Bi 2 Sr 2 CaCu 2 O 8+y (BSCCO) 1-4 . Also for the undoped AFI, band dispersions have been observed for Sr 2 CuO 2 Cl 2 5,6 . However, the band structures of the AFI and the SC are distinctly different and ARPES data have been lacking around the boundary between the AFI and the SC. In order to reveal the missing link, the present ARPES study has been performed on La 2−x Sr x CuO 4 (LSCO), which covers continuously from the SC to the AFI in a single system.In addition, the family of LSCO systems show a suppression of T c at a hole concentration δ ≃ 1/8, while the BSCCO system does not. As the origin of the anomaly at δ ≃ 1/8, the instability towards the spin-charge order in a stripe form has been extensively discussed on the basis of the incommensurate peaks in inelastic neutron scattering (INS) 7-9 . Comparing the ARPES spectra of LSCO and BSCCO will help us to clarify the impact of the stripe fluctuations.In the present paper, we discuss the novel observation of two spectral components coexisting around the SIT (x ∼ 0.05), the unusual disappearance of the Fermi surface near (π/2, π/2) in the underdoped LSCO (x ≤ 0.12) 4 , and their relevance to the stripe fluctuations.The ARPES measurements were carried out at beamline 5-3 of Stanford Synchrotron Radiation Laboratory (SSRL). Incident photons had an energy of 29 eV and were linearly polarized. The total energy resolution was approximately 45 meV and the angular resolution was ±1 degree. Single crystals of LSCO were grown by the traveling-solvent floating-zone method and then annealed so that the oxygen content became stoichiometric. The accuracy of the hole concentration δ was ±0.01. The x = 0 samples were slightly hole doped by excess oxygen so that δ ≃ 0.005 was deduced from its Néel temperature T N = 220 K 10 . The spectrometer was kept in an ultra high vacuum better than 5 × 10 −11 Torr during the measurements. The samples were cleaved ...

Electronlike Fermi surface and remnant(π,0)feature in overdopedLa1.78

“…La 2−x Sr x CuO 4 (LSCO), by virtue of the absence of these effects and the availability of high quality single crystal samples over the entire doping range, provides the opportunity to advance our understanding of the high temperature superconductors. In the underdoped regime, earlier studies have uncovered the presence of two electronic components [8][9][10] , a systematic suppression of the spectral weight near (π/2, π/2) (when compared with that of overdoped samples or BSCCO for data taken under the same conditions), and straight Fermi surface segments near (π,0) of width ∼ π/2 11,12 , which have been interpreted as evidence for electronic inhomogeneities. In the overdoped regime, an electronlike Fermi surface was observed in the high-T c superconductors for the first time 8 , but despite this progress, important problems remain.…”

Anomalous Momentum Dependence of the Quasiparticle Scattering Rate in OverdopedBi2Sr2CBogdanov1, Lanzara2, Zhou3 et al. 2002Phys. Rev. Lett.Self Cite

“…In the underdoped regime in p-type cuprates [1][2][3][4], it has been shown in many systems that the spectra near ; 0 is particularly broad. This anisotropy is generally attributed to spin scattering centered at Q ; , that for p-type cuprates in the k space connects ; 0 to 0; points of the Brillouin zone -the Fermi surface ''hot spots.''…”

Stripes in Doped Antiferromagnets: Single-Particle Spectral Weight

“…(2a) shows the experimental ARPES results for LSCO at the superconductor-insulator transition (doping x = 0.05) [12]. To enhance the structure in the obtained spectra, the authors of ref.…”

“…To enhance the structure in the obtained spectra, the authors of ref. [12] plotted the second derivative of the ARPES spectrum, so areas with high second derivative are marked white and areas with low curvature (i.e. flat intensity) are black.…”