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Register a new userA spatial interpretation of emerging superconductivity in lightly doped cuprates
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The formation of domains comprising alternating hole rich and hole poor ladders recently observed by Scanning Tunneling Microscopy by Kohsaka et al., on lightly hole doped cuprates, is interpreted in terms of an attractive mechanism which favors the presence of doped holes on Cu sites located each on one side of an oxygen atom. This mechanism leads to a geometrical pattern of alternating hole-rich and hole-poor ladders with a periodicity equal to 4 times the lattice spacing in the CuO plane, as observed experimentally. To cite this article: G. Deutscher, P.-G. de Gennes, C. R. Physique 8 (2007).
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The low-energy excitations of the lightly doped cuprates were studied by angle-resolved photoemission spectroscopy. A finite gap was measured over the entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This effect was observed to be generic to the normal states of numerous cuprates, including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to close with increasing carrier doping. We consider various scenarios to explain our results, including the possible effects of chemical disorder, electronic inhomogeneity, and a competing phase.
A central question in the high temperature cuprate superconductors is the fate of the parent Mott insulator upon charge doping. Here we use scanning tunneling microscopy to investigate the local electronic structure of lightly doped cuprate in the antiferromagnetic insulating regime. We show that the doped charge induces a spectral weight transfer from the high energy Hubbard bands to the low energy in-gap states. With increasing doping, a V-shaped density of state suppression occurs at the Fermi level, which is accompanied by the emergence of checkerboard charge order. The new STM perspective revealed here is the cuprates first become a charge ordered insulator upon doping. Subsequently, with further doping, Fermi surface and high temperature superconductivity grow out of it.
We have performed a systematic angle-resolved photoemission study of as-grown and oxygen-reduced Pr$_{2-x}$Ce$_x$CuO$_4$ and Pr$_{1-x}$LaCe$_{x}$CuO$_4$ electron-doped cuprates. In contrast to the common belief, neither the band filling nor the band parameters are significantly affected by the oxygen reduction process. Instead, we show that the main electronic role of the reduction process is to remove an anisotropic leading edge gap around the Fermi surface. While the nodal leading edge gap is induced by long-range antiferomagnetic order, the origin of the antinodal one remains unclear.
We discuss evolution of the Fermi surface (FS) topology with doping in electron doped cuprates within the framework of a one-band Hubbard Hamiltonian, where antiferromagnetism and superconductivity are assumed to coexist in a uniform phase. In the lightly doped insulator, the FS consists of electron pockets around the $(pi,0)$ points. The first change in the FS topology occurs in the optimally doped region when an additional hole pocket appears at the nodal point. The second change in topology takes place in the overdoped regime ($sim18%$) where antiferromagnetism disappears and a large $(pi,pi)$-centered metallic FS is formed. Evidence for these two topological transitions is found in recent Hall effect and penetration depth experiments on Pr$_{2-x}$Ce$_{x}$CuO$_{4-delta}$ (PCCO) and with a number of spectroscopic measurements on Nd$_{2-x}$Ce$_{x}$CuO$_{4-delta}$ (NCCO).
Using a dynamical cluster quantum Monte Carlo approximation, we investigate the effect of local disorder on the stability of d-wave superconductivity including the effect of electronic correlations in both particle-particle and particle-hole channels. With increasing impurity potential, we find an initial rise of the critical temperature due to an enhancement of anti-ferromagnetic spin correlations, followed by a decrease of Tc due to scattering from impurity-induced moments and ordinary pairbreaking. We discuss the weak initial dependence of Tc on impurity concentration found in comparison to experiments on cuprates.
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