Nematic Superconductivity in Doped Bi2Se3 Topological Superconductors

Abstract

Nematic superconductivity is a novel class of superconductivity characterized by spontaneous rotational-symmetry breaking in the superconducting gap amplitude and/or Cooper-pair spins with respect to the underlying lattice symmetry. Doped Bi 2 Se 3 superconductors, such as Cu x Bi 2 Se 3 , Sr x Bi 2 Se 3 , and Nb x Bi 2 Se 3 , are considered as candidates for nematic superconductors, in addition to the anticipated topological superconductivity. Recently, various bulk probes, such as nuclear magnetic resonance, specific heat, magnetotransport, magnetic torque, and magnetization, have consistently revealed two-fold symmetric behavior in their in-plane magnetic-field-direction dependence, although the underlying crystal lattice possesses three-fold rotational symmetry. More recently, nematic superconductivity is directly visualized using scanning tunneling microscopy and spectroscopy. In this short review, we summarize the current researches on the nematic behavior in superconducting doped Bi 2 Se 3 systems, and discuss issues and perspectives.

Z3-vestigial nematic order due to superconducting fluctuations in the doped topological insulators NbxBi2Se3 and CuxBi2Se3

“…In addition, numerous experiments have shown that the superconducting state is accompanied by a spontaneous breaking of rotational symmetry with a pronounced twofold anisotropy within the Bi 2 Se 3 basal plane [15][16][17][18][19][20][21][22] ; see Ref. 23 for a recent review. The twofold symmetry can be observed in field-angle resolved experiments where a magnetic field is rotated in the plane with respect to the crystalline axes and the corresponding physical quantity (e.g., spin susceptibility, specific heat, magneto-resistance, upper critical field, magnetization, magnetic torque) is represented as a function of angle [15][16][17][18][19][20][21][22][23] .…”

Uniaxial-strain control of nematic superconductivity in SrxBi2Se3

“…After the initial observations, nematic SC behavior has been consistently observed by using various probes such as transport, thermodynamic, and microscopic techniques [10][11][12][13][14][15][16][17][18] , as reviewed in ref. 19 . We comment here that these doped Bi 2 Se 3 nematic superconductors are quite distinct from iron pnictide superconductors, where nematicity occurs in the normal state as a consequence of orbital ordering and superconductivity eventually occurs at much lower temperatures 4 .…”

The direction of the d-vector in a nematic triplet superconductor

“…However, the specific heat measurement [20] suggests the pairing gap is maximal along y in the momentum space, hence is consistent with the D y 4 pairing instead. More experimental results are summarized nicely in [38], showing almost equal popularities of D x 4 and D y 4 pairing. Such a variety of the probed d-vectors implies the d-vector may be fragile and therefore dependent on material details, as demonstrated by our results.…”