氧化物纳米结构中通过半狄拉克点的金属-绝缘体转变：VO $_2$（001）层被限制在TiO $_2$中
Metal-insulator transition through a semi-Dirac point in oxide nanostructures: VO$_2$ (001) layers confined within TiO$_2$
摘要：
多层（TiO $_2$）$_m$ /（VO $_2$）$_n$纳米结构（$d^1$ - $d^0$界面没有极性不连续）在第一原理计算中显示相对于VO $_2$层厚度的金属-绝缘体转变。对于$n$ $\geq$ 5层，系统变为金属，而对于$n$ = 1和2，系统是绝缘的。当$n$ = 3和4时，金属-绝缘体相变通过半狄拉克点相发生，其中费米面是点状的，电子在k空间中沿带对角线方向表现为无质量，沿垂直方向表现为有质量的费米子。我们提供了一个分析的电子结构的演变，通过这一前所未有的绝缘体到金属的过渡，并确定它是由于量子限制产生一个非直观的轨道排序的V $d^1$离子，而不是一个特定的氧化物界面效应。自旋-轨道耦合不会破坏计算出的基态的半狄拉克点，其中自旋沿着金红石c轴对齐，但是如果自旋位于基面中，它确实会打开一个相当大的间隙。
英文摘要：
Multilayer (TiO$_2$)$_m$/(VO$_2$)$_n$ nanostructures ($d^1$ - $d^0$ interfaces with no polar discontinuity) show a metal-insulator transition with respect to the VO$_2$ layer thickness in first principles calculations. For $n$ $\geq$ 5 layers, the system becomes metallic, while being insulating for $n$ = 1 and 2. The metal-insulator transition occurs through a semi-Dirac point phase for $n$ = 3 and 4, in which the Fermi surface is point-like and the electrons behave as massless along the zone diagonal in k-space and as massive fermions along the perpendicular direction. We provide an analysis of the evolution of the electronic structure through this unprecedented insulator-to-metal transition, and identify it as resulting from quantum confinement producing a non-intuitive orbital ordering on the V $d^1$ ions, rather than being a specific oxide interface effect. Spin-orbit coupling does not destroy the semi-Dirac point for the calculated ground state, where the spins are aligned along the rutile c-axis, but it does open a substantial gap if the spins lie in the basal plane.
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