Abstract
By means of inelastic neutron scattering, we measured magnetic excitations in a sizable single crystal of La1.7Sr0.3Cu0.95Al0.05O4, which is an Al-substituted system of the heavily hole-doped cuprate system La2-xSrxCuO4 (LSCO) with an effective concentration of holes of xeff = 0.25. At incommensurate positions Qort = (1+δ, ±δ)/(1-δ, ±δ) around the magnetic Γ point QM = (1, 0), magnetic correlations were induced, and the incommensurability δ was 0.139 (r.l.u), which is in contrast with the δ of 0.125 (r.l.u) for LSCO x = 0.25, suggesting that the Al substitution caused an increase in δ. We also observed the same effect in the Fe-substituted system La1.7Sr0.3Cu0.95Fe0.05O4 (δ = 0.144). In addition to the obvious effect on the IC excitations, we observed continuum magnetic excitation with a ring-like shape in a two-dimmensional momentum space around QM = (1, 0). This was also observed in the Fe-substituted system, meaning that the induction/enhancement of the magnetic correlations originates from the impurity substitution, regardless of whether the impurities have magnetism. Considering our recent experimental results, revealing that the ring-like excitation also evolves in impurity-free LSCO x = 0.25 with increasing temperature, these facts suggest an intimate relationship between the temperature change and impurity substitution on the magnetic correlations and may present clues for investigating the magnetic correlations through an effective approach using impurities.
Highlights
High-transition-temperature superconductivity (SC) in copper oxide systems emerges because of carrier doping into the Mott insulating CuO2 planes in their crystal structure
We performed inelastic neutron scattering experiments to study magnetic correlations in Alsubstituted and heavily hole-doped La1.7Sr0.3Cu0.95Al0.05O4. These experiments revealed the structure of the whole magnetic excitations in a low-energy region in the Qort-ω space: the IC and ring-like excitations induced by Al-substitution, which are the same as that observed in the Fe-substitution system La1.7Sr0.3Cu0.95Fe0.05O4
The additional ring-like excitation has been observed in the pristine LSCO x = 0.25 with increasing temperature; these facts mean that, regardless of whether impurities have magnetism, they stabilize the IC excitations, corresponding to the stripe correlation, and the ring-like excitations
Summary
High-transition-temperature (high-T c) superconductivity (SC) in copper oxide systems emerges because of carrier doping into the Mott insulating CuO2 planes in their crystal structure. The antiferromagnetic correlation in the CuO2 planes, the carrier doping diminishes the static correlation, provides a strong fluctuation in their metallic phase This has been the primary candidate for gaining a pairing force for the Cooper pair while at the same time favoring a magnetic ordering, i.e., the stripe correlation, characterized by incommensurate (IC) spin structures with wave vector Qort = (1+δ, ±δ)/(1-δ, ±δ) around the original antiferromagnetic order with QM =(1, 0) in the two-dimensional plane in orthorhombic notation. This proximity makes the study of high-T c SC difficult, but it is thought to be essential. To understand this feature in detail, impurity effects have been actively studied because the concomitant randomness directly affects the lifetime of the dynamical correlations in the
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