近日，美国德克萨斯大学奥斯汀分校教授Li Shi课题组与日本国家材料科学研究所的Kenji Watanabe等人合作，并取得一项新进展，他们发现了石墨烯异质结构中可调谐的电子-弯曲声子相互作用。相关研究成果已于2023年4月26日在国际权威学术期刊《自然》上发表。

这项研究展示了在退化的石墨烯中，在约60K的温度附近出现了一个异常的洛伦兹比峰值，且随着迁移率的增加，峰值幅度会下降。通过采用多体电子-声子自能的从头计算和分析模型，该实验观测揭示了石墨烯异质结构中的反射对称性破缺现象能够降低选择定则的限制性要求，进而允许准弹性电子与奇数个弯曲声子的相互作用。这种耦合有助于将洛伦兹比增加到介于低温流体力学区域和高于120K的非弹性电子-声子散射区域之间的中间温度的Sommerfeld极限。

与以往忽略二维材料中弯曲声子对输运的贡献的研究相反，这项工作表明，可调节的电子-弯曲声子耦合可以为控制原子尺度的量子物质提供一种手段。例如，在魔角双层石墨烯中，低能激发可能介导平带电子的库珀配对。

据悉，石墨烯异质结构中观察到的超高迁移率、电子流体力学、超导和超流现象均基于独特的电子-声子相互作用特性。洛伦兹比可以通过计算电子热导率与电导率和温度的乘积之间的比值，提供对电子-声子相互作用的洞察，而这是以往石墨烯测量无法获取的信息。

附：英文原文

Title: Tunable electron–flexural phonon interaction in graphene heterostructures

Author: Sadeghi, Mir Mohammad, Huang, Yajie, Lian, Chao, Giustino, Feliciano, Tutuc, Emanuel, MacDonald, Allan H., Taniguchi, Takashi, Watanabe, Kenji, Shi, Li

Issue&Volume: 2023-04-26

Abstract: Peculiar electron–phonon interaction characteristics underpin the ultrahigh mobility¹, electron hydrodynamics^2,3,4, superconductivity⁵ and superfluidity^6,7 observed in graphene heterostructures. The Lorenz ratio between the electronic thermal conductivity and the product of the electrical conductivity and temperature provides insight into electron–phonon interactions that is inaccessible to past graphene measurements. Here we show an unusual Lorenz ratio peak in degenerate graphene near 60 kelvin and decreased peak magnitude with increased mobility. When combined with ab initio calculations of the many-body electron–phonon self-energy and analytical models, this experimental observation reveals that broken reflection symmetry in graphene heterostructures can relax a restrictive selection rule^8,9 to allow quasielastic electron coupling with an odd number of flexural phonons, contributing to the increase of the Lorenz ratio towards the Sommerfeld limit at an intermediate temperature sandwiched between the low-temperature hydrodynamic regime and the inelastic electron–phonon scattering regime above 120 kelvin. In contrast to past practices of neglecting the contributions of flexural phonons to transport in two-dimensional materials, this work suggests that tunable electron–flexural phonon couping can provide a handle to control quantum matter at the atomic scale, such as in magic-angle twisted bilayer graphene¹⁰ where low-energy excitations may mediate Cooper pairing of flat-band electrons^11,12.

DOI: 10.1038/s41586-023-05879-y

Source: https://www.nature.com/articles/s41586-023-05879-y