Ginzburg-Landau Theory with External Stress*

Cu_xBi₂Se₃ displays superconductivity[1]. It garnerns considerable interest because Bi₂Se₃ is a topological insulator. Evidence of two-fold anisotropy suggests that the superconducting phase may be nematic[2, 3]. However, the upper critical field H_c2 also appears two-fold anisotropic[3], and this actually contradicts the nematic hypothesis[4]. A pre-existing "pinning field" could break the symmetry explicitly[4], but then this casts in doubt the interpretation of any two-fold anisotropy. We study the Ginzburg-Landau theory of a nematic order parameter coupled to external stress as a pinning field. We classify possible phase diagrams, and indicate experimental signatures that might distinguish, in a pre-existing pinning field, a true nematic phase from an isotropic phase.

1. Hor et. al. PRL 104, 057001
2. Matano et. al. Nat. Phys. 12, 852
3. Yonezawa et. al. Nat. Phys 13, 123
4. Venderbos et. al. PRB 94, 094522