Zusammenfassung
NbSe2 is a prototypical charge-density-wave (CDW) material, whose
mechanism remains mysterious so far. With angle resolved photoemission
spectroscopy, we recovered the long-lost nesting condition over a
large broken-honeycomb region in the Brillouin zone, which consists
of six saddle band point regions with high density of states (DOS),
and large regions away from Fermi surfaces with negligible DOS at
the Fermi energy. We show that the major contributions to the CDW
formation come from these barely occupied states rather than the
saddle band points. Our findings not only resolve a long-standing
puzzle, but also overthrow the conventional wisdom that CDW is dominated
by regions with high DOS.
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