Electronic pairing mediated by spin fluctuations in a quantum spin ice has been studied in ( 39) for the case of a rotationally symmetric Fermi surface. 1E suggest the possibility that the Mott insulator is lightly doped due to the stacking structure, resulting in strong spin fluctuations. From this perspective, it is interesting to understand whether the proximity between the superconductor in the 1H layers and the Mott insulating state in the 1T layers is an essential ingredient. On the other hand, an attractive interaction mediated by spin fluctuations naturally prefers non–s-wave superconductivity and, in particular, chiral symmetry when the Fermi surface encloses the Γ point as given here (see Fig. In such a case, unconventional pairing is expected only if strong local repulsion, which reduces the attraction in the s-wave channel, is present. Phonon-mediated interactions typically favor s-wave pairing ( 38). We now turn to the microscopic origin of the possible chiral superconductivity. A challenging experimental goal is thus to measure a quantized thermal Hall conductance in this system. Overall, we find that the Chern number of the Chiral state is highly sensitive to the mixing ratio α ( 34). Note that the data points were computed numerically (not rounded to an integer) using the full BdG band structure with a mesh grid of 9.5 × 10 4 equally spaced points. The interpolation between these two points is plotted in Fig. On the other hand, the Chern density is cooperative in the limit α = 1, where we obtain ∁ = −6. We find that the Chern number vanishes in the limit of α = 0, i.e., ∁ = 0, because the inner and outer Fermi surfaces cancel each other. 4 (A and B) for the extreme cases α = 0 (purely d-wave) and α = 1 (purely p-wave), respectively. The phase of the superconducting order parameter in Eq. Using a tight-binding model for TaS 2 including up to the third-nearest-neighbor hopping ( 27, 33), we compute the Chern number within a BdG Hamiltonian as a function of α, allowing us to interpolate between the pure d + id- and p + ip-wave pairing channels. Consequently, it realizes a unique heterostructure of strongly correlated phases with drastically different ground states, albeit having the exact same chemical composition and almost the same structure.Ĭhiral superconductivity belongs to symmetry class D in the 10-fold way ( 32), which allows us to classify isolated 1H layers using a Chern number. Thus, 4Hb-TaS 2 is a system in which superconducting layers naturally reside in proximity to layers that have strong spin fluctuations. Recently, it was proposed that the ground state of 1T-TaS 2 is a gapless quantum spin liquid ( 16, 17, 18). The weak interlayer coupling allows us to describe 4Hb-TaS 2 as a stack of two-dimensional (2D) monolayers: 1H-TaS 2 with a locally broken inversion symmetry giving rise to antisymmetric spin-orbit coupling ( 14) and 1T-TaS 2, known as a Mott insulator that fails to order magnetically ( 15). The overall crystal is inversion symmetric, with the inversion point lying in the center of the 1T layer. 4Hb-TaS 2 belongs to the P6 3/mmc hexagonal space group, with a unit cell that consists of alternating layers of 1H-TaS 2 (half of 2H-TaS 2) and 1T-TaS 2 (see Fig.
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