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

Area of Science:

• Condensed Matter Physics
• Superconductivity
• Materials Science

Background:

• Conventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states arise from Zeeman effects breaking time-reversal symmetry in superconductors with time and inversion symmetry.
• In superconductors lacking inversion symmetry, FFLO states can form via Zeeman effects interacting with spin-orbit coupling (SOC), such as Rashba SOC.
• Ising-type SOC can suppress Zeeman effects, necessitating alternative mechanisms like orbital magnetic field coupling with SOC for FFLO states in inversion-broken superconductors.

Purpose of the Study:

• To report the discovery of an orbital FFLO state in the multilayer Ising superconductor 2H-NbSe2.
• To investigate the underlying mechanism of this unconventional FFLO state.
• To establish the phase diagram of the orbital FFLO state in 2H-NbSe2.

Main Methods:

• Transport measurements were employed to detect the orbital FFLO state.
• Analysis of symmetry breaking (translational and rotational) to identify finite-momentum Cooper pairings.
• Characterization of the phase diagram, including normal metal, uniform Ising superconducting, and six-fold orbital FFLO states.

Main Results:

• Discovery of an orbital FFLO state in 2H-NbSe2, distinct from conventional FFLO states.
• Observed breaking of translational and rotational symmetries, confirming finite-momentum Cooper pairings.
• Established the complete phase diagram, revealing a six-fold orbital FFLO state.

Conclusions:

• The study presents a novel mechanism for achieving finite-momentum superconductivity through orbital FFLO states.
• This work provides a universal pathway for realizing orbital FFLO states in superconductors with broken inversion symmetries.
• The findings in 2H-NbSe2 open new avenues for exploring unconventional superconductivity.