Observation of logarithmic Kohn anomaly in monolayer graphene

Yanchong Zhao, Luojun Du, Wei Yang, Cheng Shen, Jian Tang, Xiaomei Li, Yanbang Chu, Jinpeng Tian, Kenji Watanabe, Takashi Taniguchi, Rong Yang, Dongxia Shi, Zhipei Sun, Guangyu Zhang

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Electron-phonon coupling in monolayer graphene breaks the adiabatic Born-Oppenheimer approximation and could lead to exotic logarithmic Kohn anomaly, manifested as logarithmic singularity in optical-phonon energy. However, unraveling unambiguously the fascinating logarithmic Kohn anomaly in monolayer graphene remains challenging due to the large carrier inhomogeneity originating from the unique massless Dirac-like band dispersion and the underneath substrate doping effect. Here we demonstrate a clear signature of intriguing logarithmic Kohn anomaly in monolayer graphene with ultralow carrier inhomogeneity via h-BN encapsulation. Significantly, the magnitude of anomalous phonon softening at 25 K shows an enhancement factor of 2 as compared to that previously observed in bilayer graphene at 12 K, even though bilayer graphene with nearly parabolic band dispersion is more immune to charged impurities. The uncovered unusual logarithmic Kohn anomaly in monolayer graphene can provide a firm basis for the understanding of various peculiar physics and may shed light on the nature of superconductivity in magic-angle graphene superlattices.

Original languageEnglish
Article number165415
Number of pages6
JournalPhysical Review B
Volume102
Issue number16
DOIs
Publication statusPublished - 23 Oct 2020
MoE publication typeA1 Journal article-refereed

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