Fulde-Ferrell state in a ferromagnetic chiral superconductor with magnetic domain walls

Abstract

Motivated by the recent theoretical and experimental progress in the heavy fermion system UCoGe, we study ferromagnetic chiral superconductors in the presence of magnetic domains. Within mean field approximations, it is shown that chiral superconducting domains are naturally induced by the ferromagnetic domains. The domain wall current flows in the opposite direction to the naively expected one as in 3 He-A phase due to contributions from "unpaired electrons". Consequently, the domain wall current flows in the same direction with that of surface currents when the magnetic domain wall lies parallel to the sample surface, and therefore they contribute to the net current along the whole sample. We find that, due to the non-cancellation between the domain wall current and surface current, a Fulde-Ferrell-like superconducting state can be stabilized in an anisotropic sample for all the temperatures below the superconducting transition temperature.

Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe

“…In addition to the SIV scenario, an interesting scenario to explain the non-SC fraction is the presence of unpaired electrons related to the spontaneous charge current resulting from the FM chiral SC state [40]. The scanning SQUID measurement revealed that the FM domain wall width is ∼ 0.1-1 nm, and the size of the FM domains, an order of 10 µm, shows no large change across the SC transition [41].…”

Robust orbital diamagnetism of correlated Dirac fermions in chiral Ising universality class

“…Since the scaling contribution ∂Ψ(L/l B )/∂L = Ψ (L/l B )/l B will depend on the magnetic field B = l −2 B , the Casimir force can be controlled by B, leading to a possible sample volume change. In a confined or restricted geometry with surfaces corresponding to a real material, a finite size induced phase transition may also occur 77,78 as in a superconducting system [79][80][81] . Similarly, a temperature change in an adiabatic setup may be caused by a magnetic field in a critical Dirac system at finite temperature, where the free energy density will have a scaling form F (g = 0, l −1 B , L −1 τ ) = F 0 + Ψ(L τ /l B )/L D τ with temperature T = 1/L τ .…”