Quantum Fluctuation-driven Nematic Superfluidity of a Multi-condensate Bose Liquid: Realization in 2H-NbSe₂

Recent observations of two-fold rotational symmetry of superconductivity in certain C₃- and C₆-lattice Van der Waals materials call for microscopic mechanisms for simultaneously breaking extra symmetries accompanying superfluidity. Here, we propose a generic multi-condensate scenario of nematic superfluidity: an uneven condensation at symmetry-related momenta of lowest kinetic energy. We demonstrate the scenario via an extended Bose-Hubbard model in a two-dimensional kagome lattice. Unexpectedly, an unusual quantum fluctuation-driven nematic superfluidity emerges in a large parameter regime, exemplifying an“order by disorder” phenomenon. Given realistic parameters for 2H-NbSe₂, this mechanism offers an explanation of the observed nematic superconductivity. This study illustrates the generic nature of a multi-condensate system in breaking additional spatial and temporal symmetries, making it a convenient universal paradigm for such observations in many modern unconventional superconductors.