Quantum correction to the Langevin cross section in resonant-exchange processes

Resonant-exchange scattering plays a key role in many-body dynamics and transport phenomena (such as spin, charge, or excitation diffusion) at low and moderate temperatures. Recent investigations have shown that the locking of phase shifts is central to resonant-exchange scattering at low energies. Moreover, phase-shift locking causes an unexpected behavior, namely the resonant-exchange cross section over a broad range of energies is largely dictated by s-wave scattering, the influence of which extends high above the s-waveWigner regime. Here, we generalize our previous treatment to higher energies and derive an analytical expression for the resonantexchange cross section which depends on a few parameters and accounts not only for the locking of phase shifts, but also for their gradual unlocking with increased energy.We find good agreement between the computed (fully quantal) cross sections and those obtained with our expression, which we illustrate in great detail for the case of resonant charge transfer in ion-atom collisions.