Field-effect doping of strongly correlated electron systems

在H18期间，我们成功地制备了具有外延和非晶态CaHfO_3和DyScO_3栅绝缘层的SrTiO_3基场效应晶体管。在钛酸锶衬底上可以生长出厚度约为2 nm的CaHfO_3和DyScO_3外延绝缘层，而不会形成晶界。通过将薄外延层与非晶态绝缘体相结合，我们得到了在SrTiO3衬底的薄表面层中诱导出10^&lt；13&gt；cm^-2&gt；量级的片状载流子密度的晶体管。低温下场效应迁移率迅速增加，表明场致载流子相当于化学掺杂的载流子。在SrTiO3晶体管中观察到了从金属到绝缘体的转变，并研究了金属LaTiO3纳米线的生长。发展了一种阶梯流动生长技术，使我们能够沿退火的SrTiO3衬底的阶梯边缘制备出金属(La，Sr)TiO3纳米线阵列。提出了一种在SrTiO_3单晶表面沉积一层可促进LaTiO_3纳米线生长的SRO膜来缓冲表面的技术。这一步骤是必要的，以降低SrTiO3的表面电导率，从而使纳米线彼此隔离。最终得到的纳米线阵列具有接近理想的一维电导性能，并与课题组合作研究了Nb掺杂的钛酸锶薄膜的超导性能。特里斯科内在瑞士日内瓦大学工作。我们成功地制备了Nb：SrTiO3超导薄膜，并证明了通过静电场效应改变薄膜中的载流子浓度可以开启和关闭超导电性。

During H18 we succeeded in fabricating SrTiO3-based field-effect transistors with epitaxial and amorphous CaHfO3 and DyScO3 gate insulator layers. Epitaxial insulator layers of CaHfO3 and DyScO3 could be grown on SrTiO3 to a thickness of about 2 nm without nucleating grain boundaries. By combining a thin epitaxial layer with an amorphous insulator, we achieved transistors where sheet carrier densities of 10^<13> cm^<-2> order could be induced in a thin surface layer of a SrTiO_3 substrate. A rapid increase of the field-effect mobility was observed at low temperature, indicating that the field-induced carriers are equivalent to chemically doped carriers. A metal-to-insulator transition was observed in the SrTiO_3 transistors.The growth of metallic LaTiO_3 nanowires was studied. A step-flow growth technique was developed that allowed us to fabricate an array of metallic (La, Sr)TiO_3 nanowires along the step edges of an annealed SrTiO_3 substrate. A technique was developed to buffer the surface of an annealed SrTiO_3 single crystal surface with a SrO film pror to the growth of the LaTiO_3 nanowires. This step was necessary in order to reduce the surface conductivity of SrTiO_3 and thus isolate the nanowires from each other. The final nanowire arrays showed nearly ideal one-dimensional conductivity.The superconducting properties of Nb-doped SrTiO_3 films were studied in collaboration with the group of prof. Triscone at the University of Geneva, Switzerland. We succeeded in fabricating superconducting Nb:SrTiO_3 thin films and demonstrated that the superconductivity can be switched on and off by changing the carrier concentration in the thin films by electrostatic field effect.