An Electronic Nematic Liquid in BaNi$_2$As$_2$

TL;DR

This paper reports the discovery of strong, dynamical electronic nematic fluctuations in BaNi$_2$As$_2$, revealing a novel coupling to the crystal lattice and providing insights into nematic phases in correlated electron systems.

Contribution

It demonstrates the presence of dynamical nematic fluctuations over a wide temperature range and their unique coupling to lattice vibrations in BaNi$_2$As$_2$, a nickel-based analogue of Fe superconductors.

Findings

Strong nematic fluctuations observed above phase transition

Splitting of phonon lines without symmetry breaking

Evidence for a dynamical, lattice-coupled nematic state

Abstract

Understanding the organizing principles of interacting electrons and the emergence of novel electronic phases is a central endeavor of condensed matter physics. Electronic nematicity, in which the discrete rotational symmetry in the electron fluid is broken while the translational one remains unaffected, is a prominent example of such a phase. It has proven ubiquitous in correlated electron systems, and is of prime importance to understand Fe-based superconductors. Here, we find that fluctuations of such broken symmetry are exceptionally strong over an extended temperature range above phase transitions in \bnap, the nickel homologue to the Fe-based systems. This provides evidence for a type of electronic nematicity, dynamical in nature, which exhibits an unprecedented coupling to the underlying crystal lattice. Fluctuations between degenerate nematic configurations cause a splitting of phonon lines, without lifting degeneracies nor breaking symmetries, akin to spin liquids in magnetic systems.