Multimodal synchrotron X-ray diffraction across the superconducting transition of Sr$_{0.1}$Bi$_2$Se$_3$

TL;DR

This study uses multimodal synchrotron diffraction and resistivity measurements to investigate whether structural distortions occur in Sr$_{0.1}$Bi$_2$Se$_3$ during superconducting transition, finding no such distortions and supporting an electronic nematic order parameter.

Contribution

The paper provides direct experimental evidence that the in-plane anisotropy in Sr$_{0.1}$Bi$_2$Se$_3$ is due to electronic nematic order rather than structural distortions.

Findings

No detectable in-plane crystallographic distortion at the superconducting transition.

Supports the model of nematic superconductivity with Eu symmetry.

Structural origin of anisotropy is ruled out.

Abstract

In the doped topological insulator Sr$_x$Bi$_2$Se$_3$, a pronounced in-plane two-fold symmetry is observed in electronic properties below the superconducting transition temperature $T_c \sim$ 3 K, despite the three-fold symmetry of the observed $R\bar{3}m$ space group. The axis of two-fold symmetry is nominally pinned to one of three rotational equivalent directions and crystallographic strain has been proposed to be the origin of this pinning. We carried out multimodal synchrotron diffraction and resistivity measurements down to $\sim$0.68 K and in magnetic fields up to 45 kG on a single crystal of Sr$_{0.1}$Bi$_2$Se$_3$ to probe the effect of superconductivity on the crystallographic distortion. Our results indicate that there is no in-plane crystallographic distortion at the level of $1x10^{-5}$ associated with the superconducting transition. These results further support the model that the large two-fold in-plane anisotropy of superconducting properties of Sr$_x$Bi$_2$Sr$_3$ is not structural in origin but electronic, namely it is caused by a nematic superconducting order parameter of Eu symmetry.