Primary role of the barely occupied states in the charge density wave formation of NbSe2

TL;DR

This study reveals that in NbSe2, charge density wave formation is primarily driven by barely occupied states rather than high-density regions, challenging traditional understanding of CDW mechanisms.

Contribution

The paper demonstrates that barely occupied states play a dominant role in CDW formation in NbSe2, overturning the conventional view that high DOS regions are most influential.

Findings

Barely occupied states significantly contribute to CDW in NbSe2.

The long-standing nesting condition is mapped out over a large Brillouin zone region.

Contradicts the traditional view that high DOS regions dominate CDW formation.

Abstract

NbSe2 is a prototypical charge-density-wave (CDW) material, whose mechanism remains mysterious so far. With angle resolved photoemission spectroscopy, we mapped out the CDW gap and 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 surface with negligible DOS at the Fermi energy. We show that the major contributions to the CDW 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.