Dirac-fermion-induced parity mixing in superconducting topological insulators

Abstract

We self-consistently study surface states of superconducting topological insulators. We clarify that, if a topologically trivial bulk s-wave pairing symmetry is realized, parity mixing of pair potential near the surface is anomalously enhanced by surface Dirac fermions, opening an additional surface gap larger than the bulk one. In contrast to classical s-wave superconductors, the resulting surface density of state hosts an extra coherent peak at the induced gap besides a conventional peak at the bulk gap. We also find that no such extra peak appears for odd-parity superconductors with a cylindrical Fermi surface. Our calculation suggests that the simple U-shaped scanning tunneling microscope spectrum in CuxBi2Se3 does not originate from s-wave superconductivity, but can be explained by odd-parity superconductivity with a cylindrical Fermi surface.

Symmetry protected topological superfluid3He-B

“…On the other hand, if the Fermi surface is cylindrical, the gappless states may disappear [38,39]. The recent conflicting experimental results are consistently understandable in the context of the topological odd-parity A 1u or E u superconductivity with the Fermi surface evolution [187].…”

Pressure-induced superconductivity in the three-dimensional topological Dirac semimetal Cd3As2

“…7,8 Under pressure, Bi 2 Te 3 , Bi 2 Se 3 , Sb 2 Te 3 and Sb 2 Se 3 become superconducting, which are also regarded as candidates for TSCs. [9][10][11][12][13][14] Note that there are debates on whether these candidates are indeed TSCs, [9][10][11][12][13][14][15][16][17] therefore further experimental works are needed to definitely identify a TSC and manipulate the Majorana fermions on its surface.…”

Thermodynamic evidence for nematic superconductivity in CuxBi2Se3

“…Experimentally, the zero-bias conductance peak observed in the point-contact spectroscopy, indicating the existence of unusual surface states, evidences topological superconductivity 14 . On the other hand, a scanning tunnelling microscopy (STM) experiment on the ab-plane revealed s-wave-like tunnelling spectra 15 , which was later actually found to be inconsistent with the s-wave (∆ 1 ) scenario 16 . Rather, it was proposed that the STM spectra may be explained within the topological superconductivity scenario by taking into account the possible quasi-two-dimensional (Q2D) nature of the Fermi surface 12,17 .…”