Correlation-driven electronic nematicity in the Dirac semimetal BaNiS2

TL;DR

This study reveals electronic nematicity in BaNiS2 driven by spin-fluctuation-induced density waves, showing a unique coexistence of Dirac electrons and symmetry-breaking correlations in a low-density semimetal.

Contribution

It demonstrates the presence of correlation-driven nematicity in BaNiS2 and models its origin via a density wave framework considering spin fluctuations.

Findings

Electronic nematicity appears as C2-symmetry striped patterns.

Nematicity results from lifting degeneracy among electron pockets.

Dirac points remain unaffected by the nematic order.

Abstract

In BaNiS2 a Dirac nodal-line band structure exists within a two-dimensional Ni square lattice system, in which significant electronic correlation effects are anticipated. Using scanning tunneling microscopy, we discover signs of correlated-electron behavior, namely electronic nematicity appearing as a pair of C2-symmetry striped patterns in the local density-of-states at ~60 meV above the Fermi energy. In observations of quasiparticle interference, as well as identifying scattering between Dirac cones, we find that the striped patterns in real space stem from a lifting of degeneracy among electron pockets at the Brillouin zone boundary. We infer a momentum-dependent energy shift with d-form factor, which we model numerically within a density wave equation framework that considers spin-fluctuation-driven nematicity. This suggests an unusual mechanism driving the nematic instability, stemming from only a small perturbation to the Fermi surface, in a system with very low density of states at the Fermi energy. The Dirac points lie at nodes of the d-form factor, and are almost unaffected by it. These results highlight BaNiS2 as a unique material in which Dirac electrons and symmetry-breaking electronic correlations coexist.