Oral: Finite momentum superconductivity induced by orbital effect in an Ising superconductor

In the Bardeen– Cooper–Schrieffer (BCS) theory, Cooper pairs are formed with zero total momentum, preserving both time and inversion symmetries. A finite momentum Cooper pairing can be induced by the Zeeman effect of magnetic fields, forming the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state, characterized by a periodic spatial variation of the superconducting order parameter.

In layered superconducting transition metal dichalcogenides, such as NbSe2, the Ising-type spin-orbit coupling (SOC) strongly suppresses the Zeeman effect of external fields, thus preventing the conventional approach to the FFLO state. Nevertheless, the orbital effect of the magnetic field can shift the Fermi surfaces of layers, leading to a transition to an orbital FFLO state.

In this presentation, we provide evidence of orbital FFLO in a multilayer Ising superconductor NbSe2. Through transport studies, we reveal the symmetry transitions accompanying the phase transition from uniform Ising superconductor to the orbital FFLO state.