  Tunable magnetic interactions in high-mobility nonmagnetic semiconductor
heterostructures are centrally important to spin-based quantum technologies.
Conventionally, this requires incorporation of "magnetic impurities" within the
two-dimensional (2D) electron layer of the heterostructures, which is achieved
either by doping with ferromagnetic atoms, or by electrostatically printing
artificial atoms or quantum dots. Here we report experimental evidence of a
third, and intrinsic, source of localized spins in high-mobility GaAs/AlGaAs
heterostructures, which are clearly observed in the limit of large setback
distance (=80 nm) in modulation doping. Local nonequilibrium transport
spectroscopy in these systems reveals existence of multiple spins, which are
located in a quasi-regular manner in the 2D Fermi sea, and mutually interact at
temperatures below 100 milliKelvin via the Ruderman-Kittel-Kasuya-Yosida (RKKY)
indirect exchange. The presence of such a spin-array, whose microscopic origin
appears to be disorder-bound, simulates a 2D lattice-Kondo system with
gate-tunable energy scales.
