Strain-engineering of the charge and spin-orbital interactions in Sr2IrO4
Eugenio Paris, Yi Tseng, Ekaterina M. Pärschke, Wenliang Zhang, Mary H. Upton, Anna Efimenko, Katharina Rolfs, Daniel E. McNally, Laura Maurel, Muntaser Naamneh… 展开作者
Eugenio Paris, Yi Tseng, Ekaterina M. Pärschke, Wenliang Zhang, Mary H. Upton, Anna Efimenko, Katharina Rolfs, Daniel E. McNally, Laura Maurel, Muntaser Naamneh, Marco Caputo, Vladimir N. Strocov, Zhiming Wang, Diego Casa, Christof W. Schneider, Ekaterina Pomjakushina, Krzysztof Wohlfeld, Milan Radovic, Thorsten Schmitt
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Published in Proceedings of the National Academy of Sciences, September 2020
In the high spin-orbit coupled Sr2IrO4, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir-O bond geometry in Sr2IrO4 and perform momentum-dependent Resonant Inelastic X-ray Scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained Sr2IrO4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven crossover from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron-hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr2IrO4, originating from the modified hopping elements between the t2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr2IrO4 and provides valuable information towards the control of the ground state of complex oxides in the presence of high spin-orbit coupling.
Controlling orbital moment and spin orientation in CoO layers by strain
我们已经观察到，CoO薄膜生长在不同的衬底上显示出显着的差异，其磁性能。利用偏振相关的X射线吸收光谱在Co L $_{2,3}$边缘，我们发现，的磁矩的大小和方向强烈依赖于在薄膜中的应变引起的基板。我们提出了一个定量的模型来解释应变和自旋轨道相互作用如何决定三维轨道占据、磁各向异性以及自旋和轨道对磁矩的贡献。因此，控制的符号和方向的应变可能会打开新的机会，在交换偏置领域的应用在多层磁性薄膜。
Strain induced orbital dynamics across the Metal Insulator transition in thin VO2/TiO2(001) films
VO 2是一种强相关材料，其在加热（T= 67° C）时经历与结构相变耦合的可逆金属绝缘体转变（MIT）。自绝缘态被发现以来，绝缘态的性质一直存在争议，并提出了不同的固态机制来解释其性质：莫特-哈伯德相关，佩尔斯扭曲或两者的组合。此外，对于不同自由度之间的相互作用：电荷，晶格，轨道以及它们如何对MIT做出贡献，现在仍然缺乏共识。在这篇手稿中，我们将调查整个麻省理工学院的轨道演变引起的拉伸应变施加到薄VO 2膜。应变膜允许研究轨道和晶格自由度之间的相互作用，并澄清MIT属性。
VO2 nanosheets: controlling the THz properties through strain engineering
我们研究了应变工程二氧化钒纳米片通过外延生长在（100）R TiO 2衬底上的远红外性能。纳米片表现出大的单轴应变，导致沿金红石c轴的高度均匀和定向的裂纹。戏剧性的各向异性出现的金属-绝缘体转变温度，这是从沿cR轴的结构转变温度不同，和金属态电导率。详细的分析揭示了Mott-Hubbard沿金红石cR轴的行为。
Orbital-dependent modulation of the superconducting gap in uniaxially strained Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$
表征超导配对机制的配对对称性通常通过测量超导能隙结构（$|Δ_k|$）来确定。在这里，我们报告的测量应变引起的间隙调制（$\partial|Δ_k|$）在单轴应变Ba $_{0.6}$ K $_{0.4}$ Fe $_2$作为$_2$利用角分辨光电子能谱和$in$ - $situ$应变调谐。我们发现，单轴应变驱动Ba $_{0.6}$ K $_{0.4}$ Fe $_2$ As $_2$进入超导态，打破了超导对的四重旋转对称性。超导能隙在$d_{yz}$电子和空穴袋上增大，而在$d_{xz}$对应物上减小。这种轨道选择性表明，轨道选择性配对存在于非铁基超导体的内在。$d_{xz}$和$d_{yz}$配对通道在原始超导状态下是平衡的，但在单轴应变下变得不平衡。我们的研究结果突出了铁基超导体中轨道内散射在介导超导配对中的重要作用。它还强调了测量的$\partial|Δ_k|$作为一种有效的方法来表征超导配对从微扰的角度来看。
Anisotropic spin-density distribution and magnetic anisotropy of strained La$_{1-x}$Sr$_x$MnO$_3$ thin films: Angle-dependent x-ray magnetic circular dichroism
铁磁薄膜的磁各向异性是由衬底的外延应变通过应变诱导的轨道磁矩和自旋极化电子空间分布的各向异性引起的。然而，在铁磁金属La $_{1-x}$ Sr $_x$ MnO $_3$（LSMO）薄膜研究的X射线线性二色性（XLD）的优先轨道占领一直被发现的平面外的拉伸和压缩外延应变，因此无关的磁各向异性。为了解开这个谜团，我们直接探测自旋极化电子在LSMO薄膜中的优先轨道占领的角度相关的X射线磁性圆二色性（XMCD）的应变。自旋密度分布的各向异性被认为是在平面内的拉伸应变和平面外的压缩应变，与所观察到的磁各向异性。XLD观察到的普遍存在的面外优先轨道占据归因于表面磁死层中自旋向上和自旋向下的面外轨道的占据。
