The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magneto-resistance. These phenomena often emerge as a function of carrier doping and are rooted in the strongly correlated motion of the charge carriers and their coupling to lattice and magnetic excitations of the crystal. Here I report two parts of our recent work on the doping of a simple 2D Mott insulating system: an ordered (Ö3´Ö3)R30° lattice formed by 1/3 ML Sn adatoms adsorbed on the Si(111) surface with half-filled dangling bond orbitals. The first part is about electron doping with potassium atoms. 1/6 ML K atoms adsorbed on the surface forms a sublattice and induces a charge ordered phase in the Sn lattice. As the temperature rises, the K sublattice gradually melts and induces a series of phase transitions in the charge ordered Sn lattice. The second part if about hole doping by introducing boron dopants to the subsurface layer of the Si substrate. Hole doping metalize the Mott insulating Sn lattice, while low temperature STM/STS shows that it becomes superconducting with a critical temperature of 4.7±0.3 K. Mott correlations in the Sn-derived dangling-bond surface state suggests that the superconductivity might be unconventional.
T. Smith, F. Ming, et al., PRL 124, 097602 (2020)
X. Wu, F. Ming, et al., PRL, 125, 117001 (2020)