Orbital Fulde-Ferrell-Larkin-Ovchinnikov state in an Ising superconductor

Abstract: The conventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state relies on the Zeeman effect of an external magnetic field to break time-reversal symmetry, forming a state of finite-momentum Cooper pairing. In superconductors with broken inversion symmetries, the Rashba or Ising-type spin-orbit coupling (SOC) can interact with either the Zeeman or the orbital effect of magnetic fields, extending the range of possible FFLO states, though evidence for these more exotic forms of FFLO pairing has been lacking. Here we report the discovery of an unconventional FFLO state induced by coupling the Ising SOC and the orbital effect in multilayer 2H-NbSe2. Transport measurements show that the translational and rotational symmetries are broken in the orbital FFLO state, providing the hallmark signatures of finite momentum cooper pairings. We establish the entire orbital FFLO phase diagram, consisting of normal metal, uniform Ising superconducting phase, and a six-fold orbital FFLO state. This study highlights an alternative route to finite-momentum superconductivity and provides a universal mechanism to prepare orbital FFLO states in similar materials with broken inversion symmetries.