Breaking of Ginzburg-Landau description in the temperature dependence of the anisotropy in the nematic superconductor

TL;DR

This study investigates the temperature dependence of anisotropy in nematic superconductor Sr$_x$Bi$_2$Se$_3$, revealing deviations from Ginzburg-Landau theory predictions and challenging the strain-based symmetry breaking explanation.

Contribution

The paper presents systematic measurements of $H_{c2}$ anisotropy in Sr$_x$Bi$_2$Se$_3$, showing a smooth temperature dependence that contradicts existing Ginzburg-Landau theory predictions.

Findings

Anisotropy weakly depends on temperature below 0.8 T_c

Anisotropy decreases smoothly near T_c without singularity

Results challenge the Ginzburg-Landau description of nematic superconductors

Abstract

Nematic superconductors are characterized by an apparent crystal symmetry breaking that results in the anisotropy of the in-plane upper critical magnetic field $H_{c2}$. The symmetry breaking is usually attributed to the strain of the crystal lattice. The nature and the value of the strain are debatable. We perform systematic measurements of the $H_{c2}$ anisotropy in the high-quality Sr$_x$Bi$_2$Se$_3$ single crystals in the temperature range 1.8~K$<T<T_c\approx 2.7$~K using temperature stabilization with an accuracy of 0.0001 K. We observe that in all tested samples the anisotropy is weakly temperature dependent when $T<0.8\,T_c$ and smoothly decreases at higher temperatures without any sign of singularity when $T\rightarrow T_c$. Such a behavior {is in a drastic contradiction with the prediction of} the Ginzburg-Landau theory for the nematic superconductors. We discuss possible reasons for this discrepancy.