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

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 ${\mathrm{Sr}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ single crystals in the temperature range 1.8 $\mathrm{K}<T<{T}_{c}\ensuremath{\approx}2.7$ 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 $T\ensuremath{\rightarrow}{T}_{c}$. 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.