Two energy gaps and Fermi surface 'arcs' in NbSe2

TL;DR

This study uses ARPES to reveal two energy gaps and Fermi surface 'arcs' in NbSe2, showing how charge-density waves influence electronic structure and compete with superconductivity.

Contribution

It provides direct ARPES evidence of energy gaps caused by CDW in NbSe2 and their analogy to pseudogaps in cuprates, highlighting the impact on Fermi surface topology.

Findings

Energy gap opens in regions connected by CDW vectors.

Fermi surface breaks into 'arcs' above T0.

The gap is non-monotonic with temperature, peaking near T0.

Abstract

Using angle-resolved photoemission spectroscopy (ARPES), we report on the direct observation of the energy gap in 2H-NbSe2 caused by the charge-density waves (CDW). The gap opens in the regions of the momentum space connected by the CDW vectors, which implies a nesting mechanism of CDW formation. In remarkable analogy with the pseudogap in cuprates, the detected energy gap also exists in the normal state (T>T0) where it breaks the Fermi surface into 'arcs', it is non-monotonic as a function of temperature with a local minimum at the CDW transition temperature (T0) and it forestalls the superconducting gap by excluding the nested portions of the Fermi surface from participating in superconductivity.