Chiral and helical p -wave superconductivity in doped bilayer BiH

Abstract

We investigate the superconductivity (SC) driven by correlation effects in electron-doped bilayer BiH near a type-II van Hove singularity (vHS). By functional renormalization group, we find triplet p-wave pairing prevails in the interaction parameter space, except for spin density wave (SDW) closer to the vHS or when the interaction is too strong. Because of the large atomic spin-orbital coupling (SOC), the p-wave pairing occurs between equal-spin electrons, and is chiral and two-fold degenerate. The chiral state supports in-gap edge states, even though the low energy bands in the SC state are topologically trivial. The absence of mirror symmetry allows Rashba SOC that couples unequal spins, but we find its effect is of very high order, and can only drive the chiral p-wave into helical p-wave deep in the SC state. Interestingly, there is a six-fold degeneracy in the helical states, reflected by the relative phase angle θ = nπ/3 (for integer n) between the spin components of the helical pairing function. The phase angle is shown to be stable in the vortex state.

Plasmon Localization Assisted by Conformal Symmetry

“…Notably, our symmetry argument empowers us with deep insight into the scattering properties of these metasurfaces. Furthermore, by coupling the plasmon to large momenta, the eigenmodes of this system are extremely localized near the valley points of the structure, a feature previously studied in the context of singular surfaces [38][39][40]. Hence, the advantage of conformal metasurfaces for the enhancement of light-matter interactions is twofold: on the one hand the long dwelling of the plasmon near the excitation region opens interesting opportunities for, e.g.…”

Nonlocal effects in plasmonic metasurfaces with almost touching surfaces

“…The energy loss of the system can then be obtained by calculating the power flow at the excitation point y = 0. This power flow is then modeled as an effective surface conductivity as 17    σ er = σ x abs σ e0 a x mode σ mr = σ y abs σ m0 sin 2 θ in a y mode…”

“…in which σ e0 = Z −1 0 and σ m0 = Z 0 are the free space electric and magnetic conductivity, θ in is the incident angle and we give the expression of σ (x,y) abs in Appendix B and C. Note that Eq. 13 is just the real part of the surface conductivity, whose imaginary part can be derived using the Kramers-Kronig relations 17,28,33,34…”

“…A conventional metasurface [12][13][14][15] is characterized by two wave vectors, such that the selection of k-vectors is discretized. On the other hand, singular metasurfaces feature three wave vectors, owing to the additional length scale introduced by the singularity, which allows surface modes to exist over a continuum of quantum numbers [16][17][18] .…”

“…using the flat surface model17 , the power absorption of the a x and a y modes can be modeled as an effective surface conductivity, seeFig. 3.…”