Nonlinear twistoptics at symmetry-broken interfaces
Kaiyuan Yao, Nathan R. Finney, Jin Zhang, Samuel L. Moore, Lede Xian, Nicolas Tancogne-Dejean, Fang Liu, Jenny Ardelean, Xinyi Xu, Dorri Halbertal, K. Watanabe,… 展开作者
Kaiyuan Yao, Nathan R. Finney, Jin Zhang, Samuel L. Moore, Lede Xian, Nicolas Tancogne-Dejean, Fang Liu, Jenny Ardelean, Xinyi Xu, Dorri Halbertal, K. Watanabe, T. Taniguchi, Hector Ochoa, Ana Asenjo-Garcia, Xiaoyang Zhu, D. N. Basov, Angel Rubio, Cory R. Dean, James Hone, P. James Schuck
Broken symmetries induce strong nonlinear optical responses in materials and at interfaces. Twist angle can give complete control over the presence or lack of inversion symmetry at a crystal interface, and is thus an appealing knob for tuning nonlinear optical systems. In contrast to conventional nonlinear crystals with rigid lattices, the weak interlayer coupling in van der Waals (vdW) heterostructures allows for arbitrary selection of twist angle, making nanomechanical manipulation of fundamental interfacial symmetry possible within a single device. Here we report highly tunable second harmonic generation (SHG) from nanomechanically rotatable stacks of bulk hexagonal boron nitride (BN) crystals, and introduce the term twistoptics to describe studies of optical properties in dynamically twistable vdW systems. We observe SHG intensity modulated by a factor of more than 50, polarization patterns determined by moiré interface symmetry, and enhanced conversion efficiency for bulk crystals by stacking multiple pieces of BN joined by symmetry-broken interfaces. Our study provides a foundation for compact twistoptics architectures aimed at efficient, scalable, and tunable frequency-conversion, and demonstrates SHG as a robust probe of buried vdW interfaces.
Magnetic proximity effect at Bi$_2$Se$_3$/EuS interface with broken inversion symmetry
利用密度泛函理论（DFT）和低能有效模型研究了Bi $_2$ Se $_3$ /EuS界面对拓扑绝缘体（TI）Dirac表面态的磁邻近效应.我们考虑一个薄的铁磁绝缘体EuS膜堆叠在Bi $_2$ Se $_3$（111）三层或五层五重层（QL）的板的顶部，EuS的磁化垂直于界面（$z$轴），这打破了时间反转和反转对称性。结果表明，电荷转移和表面弛豫使狄拉克锥电子掺杂。对于3和5个量子点，顶面狄拉克锥的能隙为9 meV，而底面狄拉克锥保持无隙。这是由于EuS薄膜的短程感生磁矩引起的。对于5个量子阱，在底表面狄拉克点的正下方形成了一个能隙为2 meV的额外狄拉克锥，而对于3个量子阱，没有额外的狄拉克锥。我们还研究了自旋轨道纹理的狄拉克表面态与破坏反转对称性，使用DFT和有效的模型。我们发现，$p_z$轨道耦合到自旋矩的$z$分量，其符号与$p_x$和$p_y$轨道相反。$p_z$和径向$p$轨道以与切向$p$轨道相反的旋向性耦合到面内自旋织构。从有效模型得到的结果与我们的DFT计算一致。计算的自旋轨道织构可以从自旋极化角分辨光电子能谱测试。
Nanoscale control of perpendicular magnetic anisotropy, interfacial Dzyaloshinskii-Moriya interaction and skyrmions in the inversion-symmetry-broken Ru/Co/W/Ru films
Scaleability of dielectric susceptibility $ε_{zz}$ with the number of layers and additivity of ferroelectric polarization in van der Waals semiconductors
Spontaneous nonreciprocal transport in a gate-tunable ferromagnetic Rashba 2-dimensional electron gas
Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay（阿尔贝·费尔特实验室，法国国家科学研究中心，泰雷兹集团，巴黎萨克雷大学）；Helmholtz-Zentrum Berlin（柏林赫尔姆霍兹中心）；Institut für Physik, Martin-Luther-Universität, Halle-Wittenberg（马丁·路德哈勒-维滕贝格大学物理研究所）；Plateforme Mesures Physiques à Basses Températures, Sorbonne Université（索邦大学低温测量平台）；Saha Institute of Nuclear Physics（萨哈核物理研究所）；Max Planck Institute of Microstructure Physics（马克斯·普朗克微结构物理研究所）
