Divergence of the quadrupole-strain susceptibility of YbRu$_2$Ge$_2$; a local moment realization of electronic nematicity

TL;DR

This study demonstrates that YbRu$_2$Ge$_2$ exhibits ferroquadrupole order and diverging nematic susceptibility, providing a new platform to explore electronic nematicity in local moment intermetallics.

Contribution

The paper shows that elastoresistivity measurements effectively probe nematic susceptibility in a local moment intermetallic, expanding the understanding of electronic nematicity beyond itinerant systems.

Findings

YbRu$_2$Ge$_2$ undergoes a tetragonal-to-orthorhombic phase transition.

Elastoresistivity measurements reveal diverging nematic susceptibility.

YbRu$_2$Ge$_2$ exhibits ferroquadrupole order associated with local $4f$ orbitals.

Abstract

Ferroquadrupole order associated with local $4f$ atomic orbitals of rare earth ions is a realization of electronic nematic order. However, there are relatively few examples of intermetallic materials which exhibit continuous ferroquadrupole phase transitions, motivating the search for additional materials that fall in to this category. Furthermore, it is not clear a priori whether experimental approaches based on transport measurements which have been successfully used to probe the nematic susceptibility in materials such as the Fe-based superconductors, will be as effective in the case of $4f$ intermetallic materials, for which the important electronic degrees of freedom are local rather than itinerant and are consequently less strongly coupled to the charge-carrying quasiparticles near the Fermi energy. In the present work, we demonstrate that the intermetallic compound YbRu$_2$Ge$_2$ exhibits a tetragonal-to-orthorhombic phase transition consistent with ferroquadrupole order of the Yb ions, and go on to show that elastoresistivity measurements can indeed provide a clear window on the diverging nematic susceptibility in this system. This material provides a new arena in which to study the causes and consequences of electronic nematicity.