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Register a new userThe ground state of heavily-overdoped non-superconducting La$_{2-x}$Sr$_x$CuO$_4$
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We report detailed thermodynamic and transport measurements for non-superconducting La$_{1.7}$Sr$_{0.3}$CuO$_4$. Collectively, these data reveal that a highly-correlated Fermi-liquid ground state exists in La$_{2-x}$Sr$_x$CuO$_4$ beyond the superconducting dome, and confirm that charge transport in the cuprates is dominated at finite temperatures by intense electron-electron scattering.
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Due to the orthorhombic distortion of the lattice, the electronic hopping integrals along the $a$ and $b$ diagonals, the orthorhombic directions, are slightly different. We calculate their difference in the LDA and find $t_{a}^{prime}-t_{b}^{prime}approx 8 $meV. We argue that electron correlations in the insulating phase of La$_{2-x}$Sr$_{x}$CuO$_{4}$, i. e. at doping $xleq 0.055,$ dramatically enhance the $(t_{a}^{prime}-t_{b}^{prime}) $-splitting between the $a$- and $b$-hole valleys. In particular, we predict that the intensity of both angle-resolved photoemission and of optical absorption is very different for the $a$ and $b$ nodal points.
We have performed a temperature-dependent angle-integrated photoemission study of lightly-doped to heavily-overdoped La$_{2-x}$Sr$_{x}$CuO$_4$ and oxygen-doped La$_2$CuO$_{4.10}$. We found that both the magnitude $Delta$* of the (small) pseudogap and the temperature textit{T}* at which the pseudogap is opened increases with decreasing hole concentration, consistent with previous studies. On the other hand, the superconducting gap $Delta_{sc}$ was found to remain small for decreasing hole concentration. The results can be explained if the superconducting gap opens only on the Fermi arc around the nodal (0,0)-($pi,pi$) direction while the pseudogap opens around $sim$($pi$, 0).
Recently, several experiments on La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) challenged the Fermi liquid picture for overdoped cuprates, and stimulated intensive debates [1]. In this work, we study the magnetotransport phenomena in such systems based on the Fermi liquid assumption. The Hall coefficient $R_H$ and magnetoresistivity $rho_{xx}$ are investigated near the van Hove singularity $x_{tinytext{VHS}}approx0.2$ across which the Fermi surface topology changes from hole- to electron-like. Our main findings are: (1) $R_H$ depends on the magnetic field $B$ and drops from positive to negative values with increasing $B$ in the doping regime $x_{tinytext{VHS}}<xlesssim0.3$; (2) $rho_{xx}$ grows up as $B^2$ at small $B$ and saturates at large $B$, while in the transition regime a nearly linear behavior shows up. Our results can be further tested by future magnetotransport experiments in the overdoped LSCO.
The magnetic correlations within the cuprates have undergone intense scrutiny as part of efforts to understand high temperature superconductivity. We explore the evolution of the magnetic correlations along the nodal direction of the Brillouin zone in La2-xSrxCuO4, spanning the doping phase diagram from the anti-ferromagnetic Mott insulator at x = 0 to the metallic phase at x = 0.26. Magnetic excitations along this direction are found to be systematically softened and broadened with doping, at a higher rate than the excitations along the anti-nodal direction. This phenomenology is discussed in terms of the nature of the magnetism in the doped cuprates. Survival of the high energy magnetic excitations, even in the overdoped regime, indicates that these excitations are marginal to pairing, while the influence of the low energy excitations remains ambiguous.
We report detailed systematic measurements of the spatial variation in electronic states in the high T{c} superconductor La{2-x}Sr{x}CuO{4} (0.04<= x <= 0.16) using {63}Cu NQR for {63}Cu isotope enriched poly-crystalline samples. We demonstrate that the spatial variation in local hole concentration {63}x{local} given by {63}x{local} = x +/- {63}Dx{local}, where x is the nominal hole concentration and {63}Dx{local} is defined as the amplitude (or extent) of the spatial variation, is reflected in the frequency dependence of the spin-lattice relaxation rate {63}1/T{1} across the inhomogeneous linebroadening of the {63}Cu NQR spectrum. By using high precision measurements of the temperature dependence of {63}1/T_{1} at various positions across the {63}Cu NQR lineshape, we demonstrate that {63}Dx{local} increases below 500 - 600 K and reaches values as large as {63}Dx{local} / x ~ 0.5 in the temperature region > 150 K. By incorporating the random positioning of {+2}Sr donor ions in the lattice in a novel approach, a lower bound to the length scale of the spatial variation {63}R{patch} is deduced by fitting the entire {63}Cu NQR spectrum (including the ``B -line) using a patch-by-patch distribution of the spatial variation {63}x{local} with the patch radius {63}R_{patch} > 3.0 nm as the only free parameter. A corresponding upper bound to the amplitude of the spatial variation {63}Dx{patch} (~ 1/{63}R_{patch}) is deduced within the model, and consistent results are found with {63}Dx{local} . We also deduce the onset temperature T{Q} (> 400 K) for local orthorhombic lattice distortions which, in the region x > 0.04, is found to be larger than the onset temperature of long range structural order.
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