This paper explains why a class of bulk crystals called misfit layered compounds (MLCs) can show the same “Ising” protection of superconductivity seen in isolated two‑dimensional transition‑metal dichalcogenide (TMD) layers. The authors build a single, unified tight‑binding model — a compact way to describe how electrons hop between atoms — and fit its parameters to many density‑functional theory (DFT) calculations across different stacking orders and compositions. They find that the usually ignored tetragonal (rock‑salt) layers between the TMD slabs do more than hold charge. These layers create a sizable interlayer spin‑orbit coupling that is missing from the common “rigid‑band” picture, and this coupling is essential to reproduce the DFT electronic bands of real MLC crystals.

Misfit layered compounds are materials made from two different kinds of stacked sheets, typically written [(MX)1+δ]m[TX2]n, where M and T are metals and X is a chalcogen (S, Se, Te). Until now people often treated the hexagonal TX2 sheets as electronically isolated and the MX blocks as simple charge reservoirs. The authors instead carried out a systematic symmetry analysis and a detailed DFT study of 1H‑(TMD)/1T‑(rock‑salt) examples based on NbSe2. From those results they built momentum‑space and tight‑binding Hamiltonians that capture the low‑energy bands coming from states near the Fermi level.

A key physical point in the paper is that the tetragonal layers both weaken some direct coupling between adjacent TMD blocks and generate a distinct interlayer spin‑orbit interaction. Spin‑orbit coupling is a relativistic effect that ties an electron’s spin to its motion. In this work the new coupling locks the spin to out‑of‑plane momentum components and survives in the three‑dimensional bulk. When the authors include that interlayer spin‑orbit term in Bogoliubov–de Gennes calculations (a standard theoretical tool for superconductors), it naturally increases the in‑plane critical magnetic field. In other words, the same microscopic mechanism that gives Ising protection in monolayers can also operate in bulk MLC crystals.