We theoretically demonstrate that the high-critical-temperature (high-Tc) superconductor Bi2Sr2CaCu2O8+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.
We report the ongoing development of a Rydberg atom-based detector for sensing terahertz radiation. It will be used to characterize the emission properties of a superconducting terahertz emitter and a terahertz quantum-cascade laser.
The synthesis of Nb 4 S 3 , a previously undiscovered binary sulfide, was achieved using Nb 3 Br 7 S as a precursor. Its structure is composed of Nb 6 S triangular prisms arranged in a polar (Imm2) configuration, with sulfur atoms lying in channels along the a axis. Electrical resistivity measurements and density functional theory calculations were used to determine that Nb 4 S 3 is metallic and therefore a polar metal, with metallic bands occupied by electrons with primarily niobium character. The electrons near the Fermi level are so closely associated with the niobium sublattice that the sulfur atoms have positive Born effective charges, indicating that the electrostatic interactions between sulfur atoms are unscreened. Calculations of the dependence of the electron density on the sulfur atomic positions confirm that the metallic electrons do not screen the dipole−dipole interactions between sulfur atoms, which allows polarity and metallicity to coexist in Nb 4 S 3 . These findings suggest that applied electric fields might be able to reverse the polarity of thin films of Nb 4 S 3 .
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