1T-TaS2 在一阶电荷密度波相变中的晶格不连续性。,Scientific Reports

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1T-TaS2 在一阶电荷密度波相变中的晶格不连续性。
Scientific Reports ( IF 3.8 ) Pub Date : 2019-05-08 , DOI: 10.1038/s41598-019-43307-2
Wen Wang _{1,

2} , Dirk Dietzel ₂ , André Schirmeisen ₂

Affiliation

过渡金属二硫属化物是层状材料，由于电子-电子和电子-声子耦合的作用，可以表现出独特而显着的电子行为。在这些材料中，1T-二硫化钽（1T-TaS2）因其在不同电荷密度波（CDW）态之间的多个一级相变而引起了人们的极大兴趣。一般来说，1T-TaS2 中电荷密度波形成的基本效应可归因于相变期间 Ta 原子的平面重新取向。仅在最近几年，越来越多的研究还强调层间相互作用和堆叠顺序的作用，作为理解 1T-TaS2 特定电子行为的关键方面，特别是对于层数有限的技术系统。显然，连续监测样品的面外膨胀可以在相变期间直接提供层结构重新排列的内部情况。因此，在这封信中，我们通过原子力显微镜（AFM）方法在超高真空条件下研究了 1T-TaS2 的 c 轴晶格不连续性。我们发现，在冷却过程中，c 轴晶格经历了从近等 CDW (NC-CDW) 相到等等 CDW (C-CDW) 相变的突然收缩，而在从 C-CDW 相转变期间发现了膨胀。加热过程中从三斜 CDW 相转变为三斜 CDW 相。因此，我们的测量揭示了更高阶的 C-CDW 相如何有利于更密集的堆叠。此外，我们的测量还显示出更微妙的效应，例如相变开始时的两个膨胀峰，这可以进一步深入了解 CDW 相变开始时的机制。

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Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions.

Transition metal dichalcogenides are lamellar materials which can exhibit unique and remarkable electronic behavior due to effects of electron-electron and electron-phonon coupling. Among these materials, 1T-tantalum disulfide (1T-TaS2) has spurred considerable interest, due to its multiple first order phase transitions between different charge density wave (CDW) states. In general, the basic effects of charge density wave formation in 1T-TaS2 can be attributed to in plane re-orientation of Ta-atoms during the phase transitions. Only in recent years, an increasing number of studies has also emphasized the role of interlayer interaction and stacking order as a crucial aspect to understand the specific electronic behavior of 1T-TaS2, especially for technological systems with a finite number of layers. Obviously, continuously monitoring the out of plane expansion of the sample can provide direct inside into the rearrangement of the layer structure during the phase transition. In this letter, we therefore investigate the c-axis lattice discontinuities of 1T-TaS2 by atomic force microscopy (AFM) method under ultra-high vacuum conditions. We find that the c-axis lattice experiences a sudden contraction across the nearly-commensurate CDW (NC-CDW) phase to commensurate CDW (C-CDW) phase transition during cooling, while an expansion is found during the transition from the C-CDW phase to a triclinic CDW phase during heating. Thereby our measurements reveal, how higher order C-CDW phase can favor a more dense stacking. Additionally, our measurements also show subtler effects like e.g. two expansion peaks at the start of the transitions, which can provide further insight into the mechanisms at the onset of CDW phase transitions.

更新日期：2019-05-16

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