分子束外延$\mathrm{Ti_xO_y}$薄膜的超导相
Superconducting Phase of $\mathrm{Ti_xO_y}$ Thin Films Grown by Molecular Beam Epitaxy
摘要：
我们研究了分子束外延生长的$\mathrm{Ti_xO_y}$薄膜的结构和输运性质与生长条件之间的复杂关系。对于在850 $^{\circ}$ C下生长在（0001）- $\mathrm{Al_2 O_3}$衬底上的薄膜，通过Ti通量率和O分压$P_{Ox}$有效地调节O/Ti比，稳定了从金属性到超导性和绝缘状态的输运性质。立方$c-\mathrm{TiO_{1\pmδ}}$缓冲层在低O/Ti比下形成，而立方- $\mathrm{Ti_2 O_3}$层在较高氧化条件下形成。观察到c- $\mathrm{TiO_{1-δ}}$缓冲层的金属性。超导$\mathrm{γ-Ti_3 O_5}$ Magnéli相被发现成核的c- $\mathrm{TiO_{1-δ}}$缓冲介质$P_{Ox}$条件和绝缘体超导转变被观察到在4.5 K（T $_C^{onset}=6 K$）为85 nm厚的膜。$\mathrm{γ-Ti_3 O_5}$的应变松弛随着膜厚度的增加而发生，并且与在$\mathrm{Ti_xO_y}$薄膜中观察到的T $_C$的厚度依赖性增加相关。
英文摘要：
We investigate the complex relationship between the growth conditions and the structural and transport properties of $\mathrm{Ti_xO_y}$ thin films grown by molecular beam epitaxy. Transport properties ranging from metallicity to superconductivity and insulating states are stabilized by effectively tuning the O/Ti ratio via the Ti flux rate and the O partial pressure, $P_{Ox}$, for films grown on (0001)-$\mathrm{Al_2 O_3}$ substrates at 850$^{\circ}$ C. A cubic $c-\mathrm{TiO_{1\pmδ}}$ buffer layer is formed for low O/Ti ratios while a corundum cr-$\mathrm{Ti_2 O_3}$ layer is formed under higher oxidizing conditions. Metallicity is observed for c-$\mathrm{TiO_{1-δ}}$ buffer layers. The superconducting $\mathrm{γ-Ti_3 O_5}$ Magnéli phase is found to nucleate on a c-$\mathrm{TiO_{1-δ}}$ buffer for intermediate $P_{Ox}$ conditions and an insulator-superconducting transition is observed at 4.5 K (T$_C^{onset}=6 K$) for 85 nm thick films. Strain relaxation of the $\mathrm{γ-Ti_3 O_5}$ occurs with increasing film thickness and correlates with a thickness-dependent increase in T$_C$ observed for $\mathrm{Ti_xO_y}$ thin films.
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