| First I present the used method, which is based on positive semidefinite operator properties leading to exact particle number dependent ground states for many-body systems independent on dimensionality or integrability. After this step I describe results deduced by the method in cases where a) bare flat bands are present, or b) bare flat bands are absent, but effective (interaction-created) flat bands emerge. For references see for example PRL 91,186401(2003); PRL 99,026404(2007); PRL 105,266403(2010). |
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