Spatial inhomogeneities in single-crystal HgBa ₂CuO _4+δ from ⁶³Cu NMR spin and quadrupole shifts

⁶³Cu Nuclear Magnetic Resonance (NMR) measurements on a single crystal of the single-layer high-temperature superconductor HgBa ₂CuO _4+δ are reported. From the analysis of the quadrupolar satellites and their anisotropic splitting a largely temperature-independent symmetric quadrupole tensor is deduced, despite substantial variation in the electrical field gradients at the Cu site. The strongly temperature-dependent magnetic shifts and linewidths of the ⁶³Cu central line for different field orientations also reveal substantial spin shift variations in the material. Linear dependences on the doping of both, the quadruple splitting as well as the spin shifts, explain over a large temperature range all the widths with a local doping variation corresponding to 2δ≈0.073.