Self-generated time crystal in hybrid Josephson junctions (2501.05797v1)

Abstract: Time crystals represent a non-equilibrium state of matter with broken time-translation symmetry that repeats itself at regular time intervals. Though initially envisioned as a self-generated and self-sustained periodic motion, their realization has usually required the utilization of external periodic inputs or modulations. While at first it looked like, for a time crystal to exist, the initial proposal had to be abandoned, the recent evidence of inherent time crystals is bringing back the idea of self-generated time crystal under the spotlight. In this work, we demonstrate the appearance of a self-generated space-time crystalline order in hybrid Josephson junctions with the ferromagnet interface without any external influence. The presence of the exchange and the Dzyaloshinskii-Moriya interactions in a ferromagnet with broken structural inversion symmetry modifies the current phase relation and the critical current due to the coupling between the magnetic moment and Josephson phase. This breaks the time translation symmetry leading to the appearance of the time-crystalline order in the spatiotemporal dependence of superconducting current, which evolves with the double of the modulation frequency. Due to its unique origin and properties, this inherent time crystalline order stands out from the commonly known classification of time crystals into discrete and continuous ones. A self-generated time crystal is demonstrated in two types of hybrid Josephson junctions: the superconductor-ferromagnet-superconductor on a topological insulator and the superconductor-three layer ferromagnet-superconductor. Further, we also show that a recently developed magnetometry device that visualizes a supercurrent flow in the Josephson junction at the nanoscale can be used as a platform for experimental detection of space-time crystalline order in hybrid Josephson junctions.