the past four decades have seen tremendous efforts in determining the magnetic response of the pristine CuO2 planes in cuprate superconductors.
It is a distinct possibility that spin fluctuations are the pairing interactions in numerous unconventional superconductors. In the high-transition-temperature (high-Tc) cuprates, superconductivity emerges upon doping antiferromagnetic Mott insulators, and spin fluctuations might furthermore drive unusual pseudogap phenomena. Here we use magnetic neutron scattering to study the highly underdoped cuprate HgBa2CuO4+δ (hole concentration p ≈ 0.064). In contrast to prior results for other underdoped cuprates, we find no evidence of incommensurate magnetic order associated with spin-density-wave or stripe correlations. Instead, the antiferromagnetic response in both the superconducting and pseudogap states is gapped below ΔAF ≈ 6 meV, commensurate over a wide energy range, and disperses above about 55 meV. Given the pristine nature of HgBa2CuO4+δ, which exhibits high structural symmetry and minimal point disorder effects, this behavior likely signifies the unmasked response of the underlying CuO2 planes near the Mott-insulating state. These results serve as a benchmark for a refined theoretical understanding of the cuprates.
Z. W. Anderson, Y. Tang, V. Nagarajan, M. K. Chan, C. J. Dorow, G. Yu, D. L. Abernathy, A. D. Christianson, L. Mangin-Thro, P. Steffens, T. Sterling, D. Reznik, D. Bounoua, Y. Sidis, P. Bourges and M. Greven