Changming Yue

Abstract Flat bands have been proposed in various geometrically frustrated lattices, yet their experimental realization has been limited only to the two-dimensional (2D) kagome and three-dimensional (3D) pyrochlore lattices. While synthesizing bulk crystals with desired lattice geometry is generally challenging, the surfaces of 3D bulk materials sometimes naturally host 2D lattice structures hardly achievable in 2D bulk crystals.

The alkali-doped fulleride Cs3C60, crystallized in the space group Fm3¯m or Pm3¯n, exhibits unconventional s-wave superconductivity under pressure with a maximum Tc∼38 K. Recently, a new primitive-cubic-structured Cs3C60 phase corresponding to the space group Pa3¯ has been reported (Peng et al., arXiv:2208.09429), and the authors observed superconductivity at ambient pressure.

The anomalous self-energy plays an important role in the analysis of superconducting states. Its spectral weight provides information on the pairing glue of superconductors, but it can change in sign. In many numerical approaches, for example, Monte Carlo methods based on the Nambu formalism, the anomalous self-energy is obtained on the Matsubara axis, and nonpositive spectral weight cannot be directly obtained using the standard maximum entropy analytic continuation method.