Space-time crystalline order of a high-critical-temperature superconductor with intrinsic Josephson junctions

We theoretically demonstrate that the high-critical-temperature (high- T c ) superconductor Bi 2 Sr 2 CaCu 2 O 8+ x (BSCCO) is a natural candidate for the recently envisioned classical space-time crystal. BSCCO intrinsically forms a stack of Josephson junctions. Under a periodic parametric modulation of the Josephson critical current density, the Josephson currents develop coupled space-time crystalline order, breaking the continuous translational symmetry in both space and time. The modulation frequency and amplitude span a (nonequilibrium) phase diagram for a so-defined spatiotemporal order parameter, which displays rigid pattern formation within a particular region of the phase diagram. Based on our calculations using representative material properties, we propose a laser-modulation experiment to realize the predicted space-time crystalline behavior. Our findings bring new insight into the nature of space-time crystals and, more generally, into nonequilibrium driven condensed matter systems. A space-time crystal (STC) is a nonequilibrium phase of matter displaying long-range order in both space and time. Here, the authors propose that the high- T c cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+ x is a candidate of a classical discrete STC, when a parametric modulation periodic in time and uniform in space is applied.