Spontaneous splitting of d -wave surface states: Competition between circulating currents and edge magnetization

Journal article, 2024

Pair-breaking edges of d-wave superconductors feature Andreev bound states at the Fermi energy. Since these states are energetically highly unfavorable they are susceptible to effects that shift them to finite energy. We investigate the free energy of two different mechanisms: spontaneous phase gradients in the superconducting order parameter and surface ferromagnetism caused by Fermi liquid interaction effects. We find that the surface magnetization appears at lower temperatures than the spontaneous current flow of the phase-crystal state. The magnetic state can, however, be energetically favorable at lower temperatures for sufficiently strong Fermi liquid effects. Thus, first-order transitions between the two states as function of system temperature are possible, suggesting a rich low-temperature phase diagram in d-wave superconductors.