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Coexistence of Elastic Modulations in the Charge Density Wave State of 2H-NbSe2
Nano Letters ( IF 9.6 ) Pub Date : 2019-04-18 00:00:00 , DOI: 10.1021/acs.nanolett.9b00268 Bogdan Guster 1 , Carmen Rubio-Verdú 2 , Roberto Robles 1 , Javier Zaldívar 2 , Paul Dreher 3, 4 , Miguel Pruneda 1 , José Ángel Silva-Guillén 5 , Deung-Jang Choi 3, 4, 6 , José I. Pascual 2, 6 , Miguel M. Ugeda 2, 3, 4, 6 , Pablo Ordejón 1 , Enric Canadell 7
Nano Letters ( IF 9.6 ) Pub Date : 2019-04-18 00:00:00 , DOI: 10.1021/acs.nanolett.9b00268 Bogdan Guster 1 , Carmen Rubio-Verdú 2 , Roberto Robles 1 , Javier Zaldívar 2 , Paul Dreher 3, 4 , Miguel Pruneda 1 , José Ángel Silva-Guillén 5 , Deung-Jang Choi 3, 4, 6 , José I. Pascual 2, 6 , Miguel M. Ugeda 2, 3, 4, 6 , Pablo Ordejón 1 , Enric Canadell 7
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Bulk and single-layer 2H-NbSe2 exhibit identical charge density wave order (CDW) with a quasi-commensurate 3 × 3 superlattice periodicity. Here we combine scanning tunnelling microscopy (STM) imaging at T = 1 K of 2H-NbSe2 with first-principles density functional theory (DFT) calculations to investigate the structural atomic rearrangement of this CDW phase. Our calculations for single-layers reveal that six different atomic structures are compatible with the 3 × 3 CDW distortion, although all of them lie on a very narrow energy range of at most 3 meV per formula unit, suggesting the coexistence of such structures. Our atomically resolved STM images of bulk 2H-NbSe2 unambiguously confirm this by identifying two of these structures. Remarkably, these structures differ from the X-ray crystal structure reported for the bulk 3 × 3 CDW which in fact is also one of the six DFT structures located for the single-layer. Our calculations also show that due to the minute energy difference between the different phases, the ground state of the 3 × 3 CDW could be extremely sensitive to doping, external strain or internal pressure within the crystal. The presence of multiphase CDW order in 2H-NbSe2 may provide further understanding of its low temperature state and the competition between different instabilities.
中文翻译：
2 H -NbSe 2的电荷密度波状态下弹性调制的共存
体和单层2 H -NbSe 2表现出相同的电荷密度波阶（CDW），具有近似相称的3×3超晶格周期性。在这里，我们将扫描隧道显微镜（STM）在2 H -NbSe 2的T = 1 K下与第一原理密度泛函理论（DFT）计算相结合，以研究该CDW相的结构原子重排。我们对单层的计算表明，六种不同的原子结构与3×3 CDW畸变兼容，尽管它们全部位于每个公式单位最多3 meV的非常窄的能量范围内，表明此类结构共存。我们对大分子2 H -NbSe 2的原子分辨STM图像通过确定其中两个结构明确地确认这一点。值得注意的是，这些结构不同于报道的3×3 CDW的X射线晶体结构，实际上，这也是单层的六个DFT结构之一。我们的计算还表明，由于不同相之间的微小能量差异，3×3 CDW的基态可能对晶体中的掺杂，外部应变或内部压力极为敏感。2 H -NbSe 2中存在多相CDW有序可以进一步了解其低温状态以及不同不稳定性之间的竞争。
更新日期：2019-04-18
中文翻译：
2 H -NbSe 2的电荷密度波状态下弹性调制的共存
体和单层2 H -NbSe 2表现出相同的电荷密度波阶（CDW），具有近似相称的3×3超晶格周期性。在这里，我们将扫描隧道显微镜（STM）在2 H -NbSe 2的T = 1 K下与第一原理密度泛函理论（DFT）计算相结合，以研究该CDW相的结构原子重排。我们对单层的计算表明，六种不同的原子结构与3×3 CDW畸变兼容，尽管它们全部位于每个公式单位最多3 meV的非常窄的能量范围内，表明此类结构共存。我们对大分子2 H -NbSe 2的原子分辨STM图像通过确定其中两个结构明确地确认这一点。值得注意的是，这些结构不同于报道的3×3 CDW的X射线晶体结构，实际上，这也是单层的六个DFT结构之一。我们的计算还表明，由于不同相之间的微小能量差异，3×3 CDW的基态可能对晶体中的掺杂，外部应变或内部压力极为敏感。2 H -NbSe 2中存在多相CDW有序可以进一步了解其低温状态以及不同不稳定性之间的竞争。
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