AI 中文总结
研究扭曲双双层石墨烯中范霍夫奇点对热输运的影响，发现其能产生巨大能斯特信号，该信号可通过电场调节，理论计算表明信号增强源于里夫希茨跃迁，确立能斯特效应为费米面拓扑探针，识别出范霍夫奇点热电特征。
AI 中文摘要
扭曲的石墨烯层存在范霍夫奇点（vHSs），即态密度峰值，被认为会驱动莫尔材料中的奇异相，但其对热输运的影响尚不清楚。本文表明，扭曲双双层石墨烯（tDBLG）中的vHSs产生异常大的能斯特信号，即磁场中纵向温度梯度产生的横向电压。tDBLG导带和价带vHSs处明显的能斯特峰可通过电场调节，在约1K时最大值约为40μVK⁻¹T⁻¹，与最知名的能斯特材料相当。理论计算表明，能斯特信号的大幅增强源于vHSs周围的里夫希茨跃迁。这些发现确立了能斯特效应作为莫尔材料中费米面拓扑结构的灵敏探针，并识别出范霍夫奇点的通用热电特征。
英文摘要
Twisted graphene layers host van Hove singularities (vHSs), peaks in the electronic density of states, thought to drive exotic phases in moiré materials, but their effect on thermal transport has remained unclear. Here we show that vHSs in twisted double bilayer graphene (tDBLG) generate an unusually large Nernst signal-the transverse voltage produced by a longitudinal temperature gradient in a magnetic field. The pronounced Nernst peaks at the vHSs of the conduction and valence bands of tDBLG are tunable by an electric field with a maximum value of $\sim 40$ $μV K^{-1} T^{-1}$ at $\sim 1$ $K$, which is comparable to the best-known Nernst materials. Our theoretical calculations show that the large enhancement of the Nernst signal arises from the Lifshitz transitions around the vHSs. These findings establish the Nernst effect as a sensitive probe of Fermi-surface topology in moiré materials, and identify a universal thermoelectric signature of van Hove singularities.
