We theoretically investigate antiferromagnetic (AF) spin fluctuations in impurity-doped high-Tc superconductivity. We assume a dx2-y2-wave superconductor with strong AF spin fluctuations, and take into account nonmagnetic impurities within the t-matrix approximation. In the clean system, the imaginary part of the AF spin susceptibility (Imχ(Q,ω)) is suppressed far below the excitation gap Eg = 2 × Max[Δp] (Δp: superconducting order parameter), while it has a peak slightly below Eg. On the other hand, in the presence of unitarity scatterers, it is shown that Imχ(Q,ω) far below Eg increases with decreasing temperature even in the superconducting state. As a result, at low temperatures, Imχ(Q,ω) has two peaks far and slightly below Eg as observed in Zn-doped YBa2Cu3O6.97. In addition, because of the enhancement of the low-energy AF spin fluctuations, the nuclear spin-lattice relaxation rate on Cu ((1/T1T)Cu) also increases at low temperatures in contrast to the case of the clean superconductivity. This result can explain the recent experiment on (1/T1T)Cu in Zn-doped YBa2Cu4O8.
- Antiferromagnetic spin fluctuations
- Nonmagnetic impurity effect
- Nuclear spin relaxation
ASJC Scopus subject areas
- Physics and Astronomy(all)