Fig. 2: Magnon-cooparon effective mass variation.

Relative change in the spin stiffness δDm/Dm as a function of temperature T for different values of the static exchange field h0 induced in S. A reduction of the spin stiffness signifies an increased effective mass of the composite excitation. Tc is the critical temperature of the superconductor. Δ0 is the superconducting gap when T = h0 = 0. The dashed line plots the analytic result [Eq. (7)] obtained in the limit T → Tc.