[论文解读] Effective manipulation and realization of a colossal nonlinear Hall effect in an electric-field tunable moiré system

Jinrui Zhong, Junxi Duan+8 more|arXiv (Cornell University)|Jan 28, 2023

Quantum and electron transport phenomena被引用 4

一句话总结

本研究展示了在AB-BA堆叠的扭曲双层石墨烯中，通过电场实现对巨大二阶非线性霍尔效应的有效调控，实现了约500 μS/V·m的非线性霍尔电导率，较先前报道高出数个数量级。该效应源于贝里曲率偶极子与手性布洛赫电子侧向散射之间可调制的相互作用，且在能带边和范霍夫奇点附近，主导机制存在显著差异。

ABSTRACT

The second-order nonlinear Hall effect illuminates a frequency-doubling transverse current emerging in quantum materials with broken inversion symmetry even when time-reversal symmetry is preserved. This nonlinear response originates from both the Berry curvature dipole and the chiral Bloch electron skew scatterings, reflecting various information of the lattice symmetries, band dispersions, and topology of the electron wavefunctions. Even though many efforts have been put in detecting the nonlinear Hall effect in diverse condensed matter systems, effective manipulation of the two principal mechanisms in a single system has been lacking, and the reported response is relatively weak. Here, we report effective manipulation of the nonlinear Hall effect and realization of a colossal second-order Hall conductivity, $\sim500 μmSV^{-1}$, orders of magnitudes higher than the reported values, in AB-BA stacked twisted double bilayer graphene. A Berry-curvature-dipole-dominated nonlinear Hall effect, as well as its controllable transition to skew-scattering-dominated response, is identified near the band edge. The colossal response, on the other hand, is detected near the van Hove singularities, mainly determined by the skew scattering of the chiral Bloch electrons. Our findings establish electrically tunable moiré systems promising for nonlinear Hall effect manipulations and applications.

研究动机与目标

• 在单一量子材料体系中实现对二阶非线性霍尔效应的有效调控。
• 识别并控制非线性霍尔响应背后的主导物理机制——贝里曲率偶极子与侧向散射。
• 实现远超先前报道值数个数量级的极高的非线性霍尔电导率。
• 在莫尔异质结构中通过静电栅压实现对非线性霍尔效应的可调性。

提出的方法

• 采用AB-BA堆叠的扭曲双层石墨烯作为具有可调能带结构的莫尔体系，通过背栅调控。
• 施加电场以调节费米能级穿越能带边和范霍夫奇点。
• 测量二阶霍尔电流响应以提取非线性霍尔电导率。
• 利用理论建模区分贝里曲率偶极子与手性布洛赫电子侧向散射的贡献。
• 分析非线性霍尔响应随栅压变化的演化过程，以识别转变区域。
• 将实验结果与拓扑与输运理论预测进行比较，以确定主导机制。

实验结果

研究问题

• RQ1 如何在具有可调电子结构的单一莫尔体系中有效调控非线性霍尔效应？
• RQ2 在扭曲双层石墨烯中，贝里曲率偶极子与侧向散射对非线性霍尔响应的相对贡献是什么？
• RQ3 该体系中非线性霍尔电导率在何处以及何种条件下达到最大值？
• RQ4 贝里曲率偶极子主导与侧向散射主导区域之间的转变能否通过电场实现调控？
• RQ5 该体系中可实现的非线性霍尔电导率量级是多少，与先前报道相比如何？

主要发现

• 实验实现了约500 μS/V·m的巨大二阶非线性霍尔电导率，较先前报道值高出一个数量级。
• 在能带边附近，非线性霍尔效应主要由贝里曲率偶极子主导，通过栅压调控可清晰实现向侧向散射主导的转变。
• 非线性霍尔响应的最大值出现在范霍夫奇点附近，此时手性布洛赫电子侧向散射成为主要贡献机制。
• 该体系表现出两种不同物理机制之间的电场可调交叉，实现了对非线性霍尔效应的动态调控。
• 研究结果确立了扭曲双层石墨烯作为探索和利用非线性量子输运现象的高度可调平台。