Orbital-driven competition: Ferromagnetism and superconductivity in Li-intercalated transition metal dichalcogenides

Symmetry breaking is a fundamental concept in condensed matter physics, driving various quantum phenomena. Layered transition metal dichalcogenides (TMDs) serve as an excellent platform for investigating electronic instabilities and emergent phases. Using first-principles calculations, we reveal a striking transformation in TiSe2 and ZrSe2 induced by Li intercalation. Specifically, TiSe2 transitions from a charge density wave state to a ferromagnetic phase, while ZrSe2 evolves from a semiconductor to a superconducting state. In LiTiSe2, the localization of Ti 3d orbitals creates overlapping van Hove singularities near the Fermi level, stabilizing a Stoner-type ferromagnetic phase via exchange interactions that break spin-rotational symmetry. In contrast, superconductivity in LiZrSe2 arises from enhanced electron-phonon coupling, facilitated by delocalized Zr 4d orbitals and Zr-Zr bond-stretching phonon modes, leading to Cooper pair condensation and the breaking of U(1) gauge symmetry. These findings highlight how variations in d-orbital localization and interatomic interactions govern distinct quantum phases, demonstrating the transformative potential of intercalation for tuning electronic properties and accessing unique quantum states in layered TMDs. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)Electron-phonon couplingElectronic structureMagnetismSuperconductivityvan Hove singularity