Versatile electronic states in epitaxial thin films of (Sn-Pb-In)Te: From topological crystalline insulator and polar semimetal to superconductor
Versatile electronic states in epitaxial thin films of (Sn-Pb-In)Te: From topological crystalline insulator and polar semimetal to superconductor
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DOI：
10.1103/physrevmaterials.5.094202
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发表时间：
2021-04
影响因子：
3.4
通讯作者：
R. Yoshimi;Makoto Masuko;N. Ogawa;M. Kawamura;A. Tsukazaki;Kei S. Takahashi;M. Kawasaki;Y. Tokura
中科院分区：
文献类型：
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作者：
R. Yoshimi;Makoto Masuko;N. Ogawa;M. Kawamura;A. Tsukazaki;Kei S. Takahashi;M. Kawasaki;Y. Tokura
采用分子束外延法（MBE）成功地生长出了（Sn $_{x}$ Pb $_{1-x}$） $_{1-y}$ In $_{y}$ Te的外延薄膜，其组成范围为（0 $\leq$ x $\leq$ 1,0 $\leq$ y $\leq$ 0.23）。我们通过测量电输运和光二次谐波的产生来研究薄膜的电子相。在该系统中，可以通过调节Pb/Sn比和In组成来控制带隙反转、破坏反转对称性的电极化和费米能级位置。大量的拓扑电子相有望出现，如拓扑晶体绝缘体、拓扑半金属和超导性。对于Sn含量高（x > 0.5）的样品，空穴密度随In含量(y)的增加而增加，从而导致超导现象的出现。另一方面，对于Sn含量较低（x < 0.5）的材料，in含量的增加使空穴密度降低，载流子类型由p型转变为n型。在以(x, y) =(0.16, 0.07)为中心的n型载流子轻微掺杂的狭窄区域，出现了迁移率超过5000 cm $^{2}$ V $^{-1}$ s $^{-1}$的高迁移率电荷输运，代表了可能的半金属态。在这些样品中，光学二次谐波产生测量显示沿面外方向反转对称性被打破[111]，这保证了极性半金属态的存在。具有多种电子态的（Sn $_{x}$ Pb $_{1-x}$） $_{1-y}$ In $_{y}$ Te材料体系薄膜将成为探索新型量子现象的一个有前景的材料平台。
Epitaxial thin films of (Sn$_{x}$Pb$_{1-x}$)$_{1-y}$In$_{y}$Te were successfully grown by molecular-beam-epitaxy (MBE) in a broad range of compositions (0 $\leq$ x $\leq$ 1, 0 $\leq$ y $\leq$ 0.23). We investigated electronic phases of the films by the measurements of electrical transport and optical second harmonic generation. In this system, one can control the inversion of band gap, the electric polarization that breaks the inversion symmetry, and the Fermi level position by tuning the Pb/Sn ratio and In composition. A plethora of topological electronic phases are expected to emerge, such as topological crystalline insulator, topological semimetal, and superconductivity. For the samples with large Sn compositions (x > 0.5), hole density increases with In composition (y), which results in the appearance of superconductivity. On the other hand, for those with small Sn compositions (x < 0.5), increase in In composition reduces the hole density and changes the carrier type from p-type to n-type. In a narrow region centered at (x, y) = (0.16, 0.07) where the n-type carriers are slightly doped, charge transport with high mobility exceeding 5,000 cm$^{2}$V$^{-1}$s$^{-1}$ shows up, representing the possible semimetal states. In those samples, the optical second harmonic generation measurement shows the breaking of inversion symmetry along the out-of-plane [111] direction, which ensures the presence of polar semimetal state. The thin films of (Sn$_{x}$Pb$_{1-x}$)$_{1-y}$In$_{y}$Te materials systems with a variety of electronic states would become a promising materials platform for the exploration of novel quantum phenomena.