Evidence for Band Renormalizations in Strong-Coupling Superconducting Alkali-Fulleride Films,Physical Review Letters

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Evidence for Band Renormalizations in Strong-Coupling Superconducting Alkali-Fulleride Films
Physical Review Letters ( IF 8.1 ) Pub Date : 2023-05-26 , DOI: 10.1103/physrevlett.130.216004
J S Zhou _{1,

2} , R Z Xu _{1,

2} , X Q Yu _{1,

2} , F J Cheng _{1,

2} , W X Zhao _{1,

2} , X Du _{1,

2} , S Z Wang _{1,

2} , Q Q Zhang _{1,

2} , X Gu _{1,

2} , S M He ₃ , Y D Li _{1,

2} , M Q Ren _{1,

2} , X C Ma _{1,

2,

4} , Q K Xue _{1,

2} , Y L Chen _{3,

5,

6} , C L Song _{1,

2,

4} , L X Yang _{1,

2,

4}

Affiliation

There has been a long-standing debate about the mechanism of the unusual superconductivity in alkali-intercalated fullerides. In this Letter, using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structures of superconducting

K_{3} C_{60}

thin films. We observe a dispersive energy band crossing the Fermi level with the occupied bandwidth of about 130 meV. The measured band structure shows prominent quasiparticle kinks and a replica band involving the Jahn-Teller active phonon modes, which reflects strong electron-phonon coupling in the system. The electron-phonon coupling constant is estimated to be about 1.2, which dominates the quasiparticle mass renormalization. Moreover, we observe an isotropic nodeless superconducting gap beyond the mean-field estimation (

2 Δ / k_{B} T_{c} \approx 5

). Both the large electron-phonon coupling constant and large reduced superconducting gap suggest a strong-coupling superconductivity in

K_{3} C_{60}

, while the electronic correlation effect is suggested by the observation of a waterfall-like band dispersion and the small bandwidth compared with the effective Coulomb interaction. Our results not only directly visualize the crucial band structure but also provide important insights into the mechanism of the unusual superconductivity of fulleride compounds.

中文翻译：

强耦合超导碱富勒化物薄膜中能带重整化的证据

关于碱插层富勒烯中异常超导性的机制，长期以来一直存在争论。在这篇文章中，我们使用高分辨率角分辨光电子能谱，系统地研究了超导的电子结构

钾_{3个} C_{60}

薄膜。我们观察到一个色散能带穿过费米能级，占用带宽约为 130 meV。测量的能带结构显示出显着的准粒子扭结和涉及 Jahn-Teller 活性声子模式的复制带，这反映了系统中的强电子-声子耦合。电子-声子耦合常数估计约为 1.2，这决定了准粒子质量重整化。此外，我们观察到超出平均场估计的各向同性无节点超导间隙（