“…A special role in this context is played by the so called πphase shifts and π-pairing, i.e., antiphase relation between order parameters or equivalently the sign reversal of the effective Josephson coupling between Cooper pairs. This is at the heart of unconventional superconductivity, e.g., in cuprates [3,4], iron-based [5,6] and oxide interface superconductors [7,8], superconductor-ferromagnetsuperconductor junctions [9], phase qubits [10], electrically or orbitally driven superconducting phases [11][12][13][14],…”