Unconventional pairing from local orbital fluctuations in strongly correlated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>A</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mn>60</mml:mn></mml:msub></mml:mrow></mml:math>
Changming Yue, Shintaro Hoshino, Akihisa Koga, Philipp Werner
Abstract
The pairing mechanism in ${A}_{3}{\mathrm{C}}_{60}$ is investigated by studying the properties of a three-orbital Hubbard model with antiferromagnetic Hund coupling in the normal and superconducting phases. Local orbital fluctuations are shown to be substantially enhanced in the superconducting state, with a fluctuation energy scale that matches the low-energy peak in the spectral weight of the order parameter. Our results demonstrate that local orbital fluctuations provide the pairing glue in strongly correlated fulleride superconductors and support the spin/orbital freezing theory of unconventional superconductivity. They are also consistent with the experimentally observed universal relation between the gap energy and local susceptibility in a broad range of unconventional superconductors.