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 $\mathrm{K}<T<T_c\approx 2.7$ 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 $T<0.8T_c$ and smoothly decreases at higher temperatures without any sign of singularity when $T\to T_c$. 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.

• Received 29 July 2021
• Revised 20 October 2021
• Accepted 18 November 2021

DOI:https://doi.org/10.1103/PhysRevB.104.L220502