Itinerant ferromagnetism andp+ip′superconductivity in doped bilayer silicene

Abstract

We study the electronic instabilities of doped bilayer silicene using the random phase approximation. In contrast to the singlet d + id superconductivity at the low doping region, we find that the system is an itinerant ferromagnet in the narrow doping regions around the Van Hove singularities, and a triplet p + ip superconductor in the vicinity of these regions. Adding a weak Kane-Mele spin-orbit coupling to the system further singles out the time-reversal invariant equal-spin helical p + ip pairing as the leading instability. The triplet pairing identified here is driven by the ferromagnetic fluctuations, which become strong and enhance the superconducting critical temperature remarkably near the phase boundaries between ferromagnetism and superconductivity.

Lifshitz transition enhanced triplet $p_z$-wave superconductivity in hydrogen doped KCr$_3$As$_3$

“…The T c ∼ x relation for the p z -wave SC takes a domed shape peaking at the 3D-quasi-1D Lifshitz transition doping level. The physical origin of the triplet p z -wave SC and its dome-shaped T c ∼ x relation is related to the presence of the type-II VHSs [48][49][50][51][52] on the γ-FS, owing to its special structure consisting of two flat quasi-1D FS sheets connected by six tube-like FS sheets, as has been summarized in the last paragraph in Sec. IV.…”

“…And why the triplet p z -wave pairing is favored? The answer for the two questions lies in the presence of the type-II VHSs [48][49][50][51][52] in the band structure. To clarify this point, a thorough investigation on the evolution of the FSs with x is necessary.…”

“…Obviously, the 2D Lifshitz transitions at k z = ±k (c) z form the so-called type-II VHS [48][49][50][51][52], in which the VH momenta are not located at time-reversal variant points. It's pointed out [48][49][50][51][52] that triplet SC would generally be favored near the type-II VHS, mediated by the ferromagnetic fluctuations brought about by the strong forward scatterings there. This explains the origin of the triplet SC in the system.…”

“…Particularly, the highest T c is obtained at the Lifshitz-transition doping level. A careful investigation of the band structure suggests that the presence of the type-II VHSs [48][49][50][51][52] on the FSs are responsible for the triplet pairing, and the Lifshitz transition further favors the p zwave pairing symmetry. Our results appeal more experimental access into this intriguing superconductor hosting possible triplet p z -wave topological SC.…”

Chiral $p$-wave superconductivity in twisted bilayer graphene from dynamical mean field theory

“…Maybe. But a similar CDMFT of the nearest-neighbor Hubbard model on the graphene lattice has shown triplet pairing to be dominant [27]; so did a RPA study of bi-layer silicene [39], which is likewise based on the graphene lattice.…”