Geometrical Doping at the Atomic Scale in Oxide Quantum Materials

Chemical dopants enabling a plethora of emergent physicalpropertieshave been treated as randomly and uniformly distributed in the frameof a three-dimensional doped system. However, in nanostructured architectures,the location of dopants relative to the interface or boundary cangreatly influence device performance. This observation suggests thatchemical dopants need to be considered as discrete defects, meaningthat geometric control of chemical dopants becomes a critical aspectas the physical size of materials scales down into the nanotechnologyregime. Here we show that geometrical control of dopants at the atomicscale is another fundamental parameter in chemical doping, extendingbeyond the kind and amount of dopants conventionally used. The geometricalcontrol of dopants extends the class of geometrically controlled structuresinto an unexplored dimensionality, between 2D and 3D. It is well understoodthat in the middle of the progressive dimensionality change from 3Dto 2D, the electronic state of doped SrTiO3 is alteredfrom a highly symmetric charged fluid to a charge disproportionatedinsulating state. Our results introduce a geometrical control of dopants,namely, geometrical doping, as another axis to provide a variety ofemergent electronic states via tuning of the electronic propertiesof the solid state.