Anomalous Josephson effect

This review is devoted to one of the most relevant areas of modern condensed matter physics, the anomalous Josephson effect (AJE), which consists of the appearance of a phase shift in a hybrid structure, leading to a finite superconducting current at zero phase difference. AJE reflects the joint manifestation of superconductivity, spin-orbit interaction, and magnetism, and the study of such structures allows progress in understanding their mutual influence, while also opening up promising applications in superconducting spintronics. This review describes the physics of the $\varphi _0$ junction, the control of the magnetic properties of the barrier by means of a superconducting current, and, in turn, the effect of the magnetic moment of the barrier on the Josephson current. A discussion of new effective methods of magnetic moment reversal in the $\varphi _0$ junction, in particular, by a superconducting current pulse, as well as studies of the quantum properties of Josephson nano„structures with magnetic and topologically nontrivial barriers for the creation of new superconducting spintronic devices, is presented. The experimental realization of the $\varphi _0$ junction, which has recently been demonstrated in a number of studies by direct measurement of the current-phase relation, allows the magnitude of the spin-orbit coupling to be measured and opens up new possibilities for the phase control of Josephson devices. This research helps in understanding fundamental spin-dependent phenomena and developing applications for computer technology. In particular, control of the magnetic state by superconductivity opens up new possibilities for the development of ultrafast cryogenic memory. This review presents the results of studying the magnetic dynamics along the current–voltage characteristic of the $\varphi _0$ junction and analysis of the spin dynamics in this junction. The question of the possibility of controlling the magnetic precession by the appearance of higher harmonics in the current–phase relation, as well as the DC component of the current, which significantly increase near ferromagnetic resonance, is considered. Interesting phenomena in the $\varphi _0$ junction occur under the influence of external electromagnetic radiation. Thus, the review presents an analysis of the main theoretical and experimental work devoted to AJE, gives examples of the manifestation of AJE in various systems, indicates the prospects for research in this area, and discusses unsolved problems.