层状过渡金属硫族化合物压应力效应研究

发布时间：2018-01-08 15:05

本文关键词：层状过渡金属硫族化合物压应力效应研究　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：层状过渡金属硫族化合物(MXn,M为过渡金属元素;X = S,Se,Te)材料具有很多新奇的物理性质,成为近些年凝聚态物理领域的研究热点,例如,"11"相铁基超导体FeSe体系、以及光电半导体材料MX2(M = Mo,W;X= S,Se)体系等。在铁基超导体中,FeSe的结构和组分最为简单,常压下FeSe的超导临界温度Tc仅有9 K左右,但Tc灵敏于结构和微结构的变化,在高压、或单层薄膜体系中超导转变温度Tc可以提高到37 K和100 K以上。与FeSe不同,MX2是一种具有层状六方结构的半导体材料,在光电子学领域中具有广阔的应用前景,该体系的光电性能、能带结构也灵敏地依赖于结构和微结构性质。压力是调节凝聚态体系结构和微结构的有效手段,通过研究外加压力、薄膜衬底压应力效应、元素替代产生的化学压等因素对材料结构、磁性、电学性质等的影响,可以揭示很多深层次的物理本源。本论文以"11"铁基超导体FeSe、母体FeTe、以及光电半导体材料WSe2为研究对象,研究了衬底压应力对FeSe薄单晶样品超导电性的调控;FeTe中Sb元素替代效应对电输运性质等的影响;外加压力对WSe2的结构和电学性质的调控。本论文共分为五章:第一章,概述了 "11"相铁基超导体Fe(Te,Se)体系以及半导体过渡金属二硫化物MX2(M = Mo,W;X = S,Se)的研究背景以及研究现状。第二章,双轴压应力对FeSe超导电性的增强效应。我们制备了高质量的FeSe单晶,通过商用胶带剥离块材FeSe单晶的方法获得厚度约几百纳米的薄单晶样品。研究表明,在该压应力作用下,超导临界温度Tc比块材样品的9K提升了 30%-40%,上临界磁场Hc2比块材样品的≈14.8 T提高了～20%;同时,表征自旋涨落增强的特征温度从69 K提高到87 K,然而,结构相变/电子向列相变温度94K在压应力作用下降低了～5 K。我们的结果给出了 FeSe中超导电性、向列有序态和自旋涨落等在压应力下的演化过程,为研究三者之间内在关联提供了依据。第三章,FeTe中Te位替代效应对结构、输运和磁性的有效调控。我们成功合成了 FeTe1-xSbx系列单晶样品,研究了 Sb取代Te所产生的化学压力对FeTe磁性和结构性质的影响。研究表明,随着Sb含量的增加,面内晶格常数a逐渐增加,而面外晶格常数c逐渐收缩,等效于面外单轴压力效应。电阻率、磁化率及比热测量结果一致表明,随着Sb含量的增加,体系的反铁磁/结构转变温度TN从母体的70 K逐渐降低,表明低温反铁磁有序态被逐渐抑制。霍尔系数测量表明Sb替代Te引入了空穴载流子,但并未诱导出超导电性,这一点与基于巡游磁性的铁砷体系中可以通过电子或空穴掺杂诱导超导电性不同。我们的结果表明,FeTe的磁性更加符合基于超交换相互作用的局域自旋模型。第四章,WSe2中压力诱导的等结构相变和金属化。我们在高达62.8 GPa的压力条件下系统地研究了层状光电半导体WSe2结构和电性质,给出了高压诱导等结构相变和金属化的直接实验证据。一方面,利用原位高压同步辐射X射线衍射和拉曼光谱实验技术,我们发现在28 GPa左右衍射图谱明显展宽并且轴向比c/a出现显著的扭折,同时拉曼峰发生劈裂,这些结果一致表明WSe2发生了高压诱导的等结构相变,此外我们还发现直到最高压力低压和高压结构相仍然是共存的,进一步分析表明该等结构相变是面内压缩和层间滑移共同作用的结果。另一方面,电输运实验测量结果表明伴随着等结构相变出现了部分金属化,随着压力继续增加该金属化在1.8-300 K的范围内变得越来越占主导,但由于两相共存直到最高压力金属化仍未彻底完成。第五章,总结与展望。
[Abstract]:Layered transition metal chalcogenides (MXn, M transition metal elements; X = S, Se, Te) materials have many novel physical properties, become the hot research field in recent years condensed state physics, for example, the "11" phase iron based superconductor FeSe system, and the photoelectric semiconductor material MX2 (M = Mo W, X= S, Se); system. In iron-based superconductors, the structure and component of FeSe is the most simple, the superconducting critical temperature Tc under atmospheric pressure FeSe only about 9 K, but the changes in Tc sensitive structure and micro structure under high pressure or thin film system in superconducting transition temperature Tc can be increased to more than 37 K and 100 K. Unlike FeSe, MX2 is a semiconductor material with a layered structure of the six party, and has broad application prospects in the fields of Optoelectronics and optoelectronic properties of the system, the band structure is sensitive to the structure and properties of micro structure. The pressure regulation is condensed the system structure and the micro Effective means of structure, the external pressure through research, thin film substrate stress magnetic effect, chemical pressure and other factors of element substitution on the structure of the material, and the influence of electrical properties, can reveal the physical origin of many deep level. This thesis takes "11" iron based superconductor FeSe, matrix FeTe and photoelectric semiconductor WSe2 material as the research object, to study the substrate stress regulation of FeSe thin single crystal samples of superconductivity; effects of Sb elements in the FeTe substitution effect on electrical transport properties; external pressure regulating structure and electrical properties of WSe2. This paper is divided into five chapters: the first chapter outlines "11" iron based superconductor Fe (Te, Se) and transition metal sulfide semiconductor system two MX2 (M = Mo, W; X = S, Se) the research background and research status. The second chapter, biaxial compressive stress on the enhancement effect of FeSe superconductivity. We prepared the high quality the FeSe single Get a thin crystal, single crystal samples with thickness of about several hundred nanometers by tape stripping method for commercial FeSe bulk single crystal. The results show that the compressive stress, the superconducting critical temperature of Tc increased 30%-40% than the bulk samples of 9K, the upper critical field Hc2 increased to more than 20% in bulk samples is 14.8 T; at the same time, the characteristics of characterization of the spin fluctuation enhanced temperature increased from 69 K to 87 K, however, structural transition / electronic nematic phase transition temperature of 94K in compressive stress was reduced to 5 K. our results are given FeSe super conductivity, to the evolution of ordered state and the spin fluctuations in pressure stress, provide according to the internal relationship between the three. The third chapter is the research of FeTe Te, a substitution effect on the structure, effective regulation and control of transport and magnetism. We successfully synthesized the FeTe1-xSbx series of single crystal samples, the effects of substituting Sb chemical pressure generated by Te on FeTe magnetic Effect and structural properties. The results show that with the increase of Sb content, the in-plane lattice constant a increases gradually, and the out of plane lattice constant of C gradually shrink, equivalent to the surface effect of uniaxial stress. The resistivity, magnetic susceptibility and specific heat measurements. The results showed that with the increase of Sb content, the anti ferromagnetic / system structure transition temperature TN from the maternal 70 K decreased gradually, indicating that low temperature antiferromagnetic ordering is gradually suppressed. Holzer coefficient measurements show that the substitution of Sb Te into the hole, but did not induce superconductivity, and this system based on the magnetic iron arsenic parade may be doped with electron or hole induced superconductivity different. Our results show that FeTe is more consistent with the magnetic superexchange interaction model based on local spin. In the fourth chapter, such as structural transformation and metal induced stress in WSe2. We at pressure up to 62.8 GPa under the condition of Systematic study of the layered structure and electrical properties of WSe2 semiconductor optoelectronics, provides direct experimental evidence for pressure induced structure phase transition and metallization. On the one hand, using in-situ high-pressure synchrotron radiation X ray diffraction and Raman spectroscopy experimental techniques, we found that around 28 GPa diffraction spectrum is broadened significantly and axial ratio c/a kink significantly at the same time, the Raman peaks split, these results show the occurrence of pressure induced structure transition of WSe2, we also found that the highest pressure until the low and high pressure phase structure is still coexist, further analysis shows that the structure transformation is the in-plane compression and interlaminar slip together. On the other hand electrical transport, experimental results show that with the other part of the structural transition metal, with pressure continued to increase the metal in the range of 1.8-300 K becoming increasingly dominant Guide, but due to the coexistence of two phases until the maximum pressure metallization is still not completely completed. The fifth chapter, summary and prospect.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O511.3

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