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Strongly Compressed Few-Layered SnSe2 Films Grown on a SrTiO3 Substrate: The Coexistence of Charge Ordering and Enhanced Interfacial Superconductivity
Nano Letters ( IF 9.6 ) Pub Date : 2019-07-09 00:00:00 , DOI: 10.1021/acs.nanolett.9b01766
Zhibin Shao 1 , Zhen-Guo Fu 2 , Shaojian Li 1 , Yan Cao 1 , Qi Bian 1 , Haigen Sun 1 , Zongyuan Zhang 1 , Habakubaho Gedeon 1 , Xin Zhang 1 , Lijun Liu 1 , Zhengwang Cheng 1 , Fawei Zheng 2 , Ping Zhang 2 , Minghu Pan 1
Nano Letters ( IF 9.6 ) Pub Date : 2019-07-09 00:00:00 , DOI: 10.1021/acs.nanolett.9b01766
Zhibin Shao 1 , Zhen-Guo Fu 2 , Shaojian Li 1 , Yan Cao 1 , Qi Bian 1 , Haigen Sun 1 , Zongyuan Zhang 1 , Habakubaho Gedeon 1 , Xin Zhang 1 , Lijun Liu 1 , Zhengwang Cheng 1 , Fawei Zheng 2 , Ping Zhang 2 , Minghu Pan 1
Affiliation
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High pressure has been demonstrated to be a powerful approach of producing novel condensed-matter states, particularly in tuning the superconducting transition temperature (Tc) of the superconductivity in a clean fashion without involving the complexity of chemical doping. However, the challenge of high-pressure experiment hinders further in-depth research for underlying mechanisms. Here, we have successfully synthesized continuous layer-controllable SnSe2 films on SrTiO3 substrate using molecular beam epitaxy. By means of scanning tunneling microscopy/spectroscopy (STM/S) and Raman spectroscopy, we found that the strong compressive strain is intrinsically built in few-layers films, with a largest equivalent pressure up to 23 GPa in the monolayer. Upon this, unusual 2 × 2 charge ordering is induced at the occupied states in the monolayer, accompanied by prominent decrease in the density of states (DOS) near the Fermi energy (EF), resembling the gap states of CDW reported in transition metal dichalcogenide (TMD) materials. Subsequently, the coexistence of charge ordering and the interfacial superconductivity is observed in bilayer films as a result of releasing the compressive strain. In conjunction with spatially resolved spectroscopic study and first-principles calculation, we find that the enhanced interfacial superconductivity with an estimated Tc of 8.3 K is observed only in the 1 × 1 region. Such superconductivity can be ascribed to a combined effect of interfacial charge transfer and compressive strain, which leads to a considerable downshift of the conduction band minimum and an increase in the DOS at EF. Our results provide an attractive platform for further in-depth investigation of compression-induced charge ordering (monolayer) and the interplay between charge ordering and superconductivity (bilayer). Meanwhile, it has opened up a pathway to prepare strongly compressed two-dimensional materials by growing onto a SrTiO3 substrate, which is promising to induce superconductivity with a higher Tc.
中文翻译：
在SrTiO 3衬底上生长的强压缩几层SnSe 2薄膜：电荷有序和增强的界面超导性共存
高压已被证明是产生新型凝聚态的有力方法，尤其是在不涉及化学掺杂复杂性的情况下，以干净的方式调节超导性的超导转变温度（T c）。然而，高压实验的挑战阻碍了对潜在机理的进一步深入研究。在这里，我们已经成功地在SrTiO 3上合成了可连续层控制的SnSe 2膜衬底采用分子束外延。通过扫描隧道显微镜/光谱学（STM / S）和拉曼光谱学，我们发现强压缩应变本质上是建立在几层薄膜中的，单层中的最大等效压力高达23 GPa。在此基础上，在单层的占据态中诱导出异常的2×2电荷有序，伴随着费米能量（E F）附近的态密度（DOS）的显着降低。），类似于过渡金属二卤化碳（TMD）材料中报道的CDW的间隙状态。随后，由于释放了压缩应变，在双层膜中观察到了电荷有序化和界面超导性的共存。结合空间分辨光谱研究和第一性原理计算，我们发现仅在1×1区域中观察到增强的界面超导性，估计T c为8.3K。这种超导性可以归因于界面电荷转移和压缩应变的共同作用，这导致导带最小值的大幅下降和E F下DOS的增加。。我们的结果为进一步深入研究压缩诱导的电荷有序性（单层）以及电荷有序性和超导性（双层）之间的相互作用提供了一个有吸引力的平台。同时，它开辟了一条途径，可以通过在SrTiO 3衬底上生长制备强压缩的二维材料，从而有望以更高的T c诱导超导。
更新日期：2019-07-09
中文翻译：
在SrTiO 3衬底上生长的强压缩几层SnSe 2薄膜：电荷有序和增强的界面超导性共存
高压已被证明是产生新型凝聚态的有力方法，尤其是在不涉及化学掺杂复杂性的情况下，以干净的方式调节超导性的超导转变温度（T c）。然而，高压实验的挑战阻碍了对潜在机理的进一步深入研究。在这里，我们已经成功地在SrTiO 3上合成了可连续层控制的SnSe 2膜衬底采用分子束外延。通过扫描隧道显微镜/光谱学（STM / S）和拉曼光谱学，我们发现强压缩应变本质上是建立在几层薄膜中的，单层中的最大等效压力高达23 GPa。在此基础上，在单层的占据态中诱导出异常的2×2电荷有序，伴随着费米能量（E F）附近的态密度（DOS）的显着降低。），类似于过渡金属二卤化碳（TMD）材料中报道的CDW的间隙状态。随后，由于释放了压缩应变，在双层膜中观察到了电荷有序化和界面超导性的共存。结合空间分辨光谱研究和第一性原理计算，我们发现仅在1×1区域中观察到增强的界面超导性，估计T c为8.3K。这种超导性可以归因于界面电荷转移和压缩应变的共同作用，这导致导带最小值的大幅下降和E F下DOS的增加。。我们的结果为进一步深入研究压缩诱导的电荷有序性（单层）以及电荷有序性和超导性（双层）之间的相互作用提供了一个有吸引力的平台。同时，它开辟了一条途径，可以通过在SrTiO 3衬底上生长制备强压缩的二维材料，从而有望以更高的T c诱导超导。
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