Superconductivity in two-dimensional compounds is widely concerned, not only due to its application in constructing nano-superconducting devices, but also for the general scientific interests. Very recently, borophene (two-dimensional boron sheet) has been successfully grown on the Ag(111) surface, through direct evaporation of a pure boron source. The experiment unveiled two types of borophene structures, namely β12 and χ3. Herein, we employed density-functional first-principles calculations to investigate the electron-phonon coupling and superconductivity in both structures of borophene. The band structures of β12 and χ3 borophenes exhibit inherent metallicity. We found electron-phonon coupling constants in the two compounds are larger than that in MgB2. The superconducting transition temperatures were determined to be 18.7 K and 24.7 K through McMillian-Allen-Dynes formula. These temperatures are much higher than theoretically predicted 8.1 K and experimentally observed 7.4 K superconductivity in graphene. Our findings will enrich the nano-superconducting device applications and boron-related material science.

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The recently discovered kagome family AV3Sb5 (A = K, Rb, Cs) exhibits rich physical phenomena, including non-trivial topological electronic structure, giant anomalous Hall effect, charge density waves (CDW) and superconductivity. Notably, CDW in AV3Sb5 is evidenced to intertwine with its superconductivity and topology, but its nature remains elusive. Here, we combine x-ray diffraction experiments and density-functional theory calculations to investigate the CDWs in CsV3Sb5 and demonstrate the coexistence of 2 × 2 × 2 and 2 × 2 × 4 CDW stacking phases. Competition between these CDW phases is revealed by tracking the temperature evolution of CDW intensities, which also manifests in different transition temperatures during warming-and cooling-measurements. We also identify a meta-stable quenched state of CsV3Sb5 after fast-cooling process. Our study demonstrates the coexistence of competing CDW stackings in CsV3Sb5, offering new insights in understanding the novel properties of this system.