Abstract
We have carried out neutron spectroscopic measurements on single crystals of ${\mathrm{La}}_{1.6\ensuremath{-}x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ from $0.12\ensuremath{\le}x\ensuremath{\le}0.26$ using time-of-flight techniques. These measurements allow us to follow the evolution of parallel spin stripe fluctuations with energies less than $\ensuremath{\sim}33$ meV, from $x=0.12$ to 0.26. Samples at these hole-doping levels are known to display static (on the neutron-scattering time scale) parallel spin stripes at low temperature, with onset temperatures and intensities which decrease rapidly with increasing $x$. Nonetheless, we report remarkably similar dynamic spectral weight for the corresponding dynamic parallel spin stripes, between 5 and 33 meV, from the 1/8 anomaly near $x=0.12$, to optimal doping near $x=0.19$ to the quantum critical point for the pseudogap phase near $x=0.24$, and finally to the approximate end of superconductivity near $x=0.26$. This observed dynamic magnetic spectral weight is structured in energy with a peak near 17 meV at all dopings studied. Earlier neutron and resonant x-ray scattering measurements on related cuprate superconductors have reported both a disappearance with increasing doping of magnetic fluctuations at ($\ensuremath{\pi}$, $\ensuremath{\pi}$) wave vectors characterizing parallel spin stripe structures and persistant paramagnon scattering away from this wave vector, respectively. Our results for ${\mathrm{La}}_{1.6\ensuremath{-}x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ from 0.12 $\ensuremath{\le}x\ensuremath{\le}0.26$ clearly show persistent parallel spin stripe fluctuations at and around at ($\ensuremath{\pi}$, $\ensuremath{\pi}$), and across the full range of doping studied. These results are also compared to recent theory. Together with a rapidly declining $x$ dependence to the static parallel spin stripe order, the persistent parallel spin stripe fluctuations show a remarkable similarity to the expectations of a quantum spin glass, random t-J model, recently introduced to describe strong local correlations in cuprates.
Highlights
High temperature superconductivity in hole-doped cuprates arises from the presence of mobile holes in the quasi-two-dimensional (2D) CuO2 layers, introduced by chemical doping
Our present results show clearly that the spectral weight for dynamic parallel spin stripes around (π, π ) wave vectors below ∼33 meV in Nd-LSCO change relatively little with hole doping from the 1/8 anomaly at x = 0.12, to optimal doping at x = 0.19, through the pseudogap quantum critical point at x = 0.24 and x = 0.26, the latter of which is close to the end of the superconducting dome
We have carried out TOF inelastic neutron-scattering measurements on single crystals of Nd-LSCO with hole doping, x, ranging from the 1/8 anomaly at x = 0.12 to optimal doping at x = 0.19, to just beyond the pseudogap quantum critical point at x = 0.24, to the end of the superconducting dome, at x = 0.26
Summary
High temperature superconductivity in hole-doped cuprates arises from the presence of mobile holes in the quasi-two-dimensional (2D) CuO2 layers, introduced by chemical doping. Using a tetragonal unit cell, for which a = b = 3.88 Å, diffraction from diagonal spin stripe order is first observed at low doping with quasi-Bragg peaks at four positions split off from the ( 21 , 21 , 0), or (π , π , 0), position in reciprocal space [6]. Wakimoto and collaborators made the remarkable discovery that the incommensurate pattern of quasi-Bragg peaks in LSCO rotates within the a∗-b∗ plane of reciprocal space by 45◦, to ordering wave vectors of the form ( 21 , 21 ± δ, 0) and ( 21 ± δ, 21 , 0), forming parallel spin stripe order, at x = 0.05, which is the onset of superconducting ground states in LSCO [10]. A similar rotation between so-called diagonal and parallel spin stripe magnetism has been observed in LBCO and Nd-LSCO [11–14]
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