Magnetic field driven nodal topological superconductivity in monolayer transition metal dichalcogenides

Abstract

Recently, Ising superconductors which possess in-plane upper critical fields much larger than the Pauli limit field are under intense experimental study. Many monolayer or few layer transition metal dichalcogenides are shown to be Ising superconductors. In this work, we show that in a wide range of experimentally accessible regimes where the in-plane magnetic field is higher than the Pauli limit field but lower than Hc2, a 2H-structure monolayer NbSe2 or simiarly TaS2 becomes a nodal topological superconductor. The bulk nodal points appear on the Γ − M lines of the Brillouin zone where the Ising SOC vanishes. The nodal points are connected by Majorana flat bands, similar to the Weyl points being connected by surface Fermi arcs in Weyl semimetals. The Majorana flat bands are associated with a large number of zero energy Majorana fermion edge modes which induce spin-triplet Cooper pairs. This work demonstrates an experimentally feasible way to realise Majorana fermions in nodal topological superconductor, without any fining tuning of experimental parameters.

Robust parity-mixed superconductivity in disordered monolayer transition metal dichalcogenides

“…The tight-binding parameters that fit the transition metal dominated bands in 1H-NbSe 2 were adapted from reference [33], and are listed in table II. The Fourier transform of our real-space tight-binding model in equation (2) with all the hoppings t µν ij given in table III yields the k-space tight-binding model developed by Liu et al [47].…”

“…. The diagonal intraorbital pairing correlations in (33) are the only ones that form the superconducting order parameters ∆ µ iσσ = (iσ y ) σσ U µ Ψ µµ ii,σσ , which converge self-consistently. After reaching self-consistent convergence for the (necessarily real and singlet) diagonal elements, we probe the content of the off-diagonal elements.…”

Chiral superconductivity in the alternate stacking compound 4Hb-TaS 2

“…That is, we compute the Chern number independently from the crystal momentum along z. Using the tight-binding model for TaS 2 up to the third nearest neighbor hopping [27][28][29], we compute the 2D Chern number within a BdG Hamiltonian as a function of α, allowing us to interpolate between the pure d− and p-wave pairing channels. First, we note that each one of the two non-degenerate spin bands contribute to the total Chern density.…”

Topological superconductivity from magnetic impurities on monolayer NbSe2

“…Therefore in a first approximation the effect of Se atoms is incorporated in an effective Hamiltonian for the triangular sublattice of Nb atoms. 80,81 The Hamiltonian has to meet the symmetry requirements of the underlying triangular lattice [see Fig. 1(a)].…”