Vestigial nematic phase due to superconductivity in doped Bi2Se3, and its influence on the superconducting ground state in an applied magnetic field

Under Cu or Nb doping, the topological insulator Bi₂Se₃ becomes superconducting with a maximal T_c~3-4 K. The pairing symmetry has been intensely studied and in recent years, experiments have consistently pointed towards an unconventional, odd-parity triplet pairing in the two-dimensional irreducible representation E_u of the crystal point group D_3d. Due to a low carrier density and a small ratio of the superconducting coherence length and the Fermi wavelength, fluctuations are increasingly important, even to the extent that they allow for a preformed nematic state with T_n> T_c. Inside this performed phase, we study resistivity, elastic constants, and fluctuating diamagnetism. Furthermore, we investigate how the superconducting ground state in a constant magnetic field is affected by the preformed phase.