Search

In this study, we numerically calculate the temperature distribution and the THz phase dynamics in the mesa-structured intrinsic Josephson junctions (IJJs) using the thermal diffusion equation and the Sine–Gordon equation. We observe that the temperature distribution has a broad peak around the center region of the IJJ mesa. Under a high external current, a “hot spot” where the temperature is locally higher than the superconducting critical temperature appears around this region. The transverse Josephson plasma wave is strongly excited by the inhomogeneous temperature distribution in the mesa. This gives rise to intense THz emission.

The microscopic theory of Josephson junction due to Ambegaokar, Eckern, and Schon is generalized to allow for the spatial variation of the superconducting order parameter in the vicinity of the junction plane, and to allow the coupling of phase difference to the external electromagnetic field. A few mechanisms of dissipation in phase dynamics are discussed. Leakage resistance observed down to lowest temperatures is explained on the basis of our calculation.

We formulate a Ginzburg Landau theory for the resonating valence bond model of antiferromagnetism and high Tc superconductivity, the order parameter of which are complex link variables. We investigate the dynamics of their phase part by Monte Carlo mothod and obtain an indication of a transition to a superconducting phase. When the doping parameter is zero, the theory becomes equivalent to a U(1) lattice gauge theory in two dimension.

We investigate the longitudinal phase dynamics in an intrinsic Josephson-junction array with alternating junction parameters on the basis of the capacitive coupling model. The coupled dynamical equations for the phase differences are derived. The linear dynamics in this system yields two collective phase modes propagating along the c-direction, which are identified with the two longitudinal Josephson-plasma modes observed in the T ∗ -structure high-Tc cuprates. The non-linear phase dynamics in this system shows the existence of stable localized rotating modes, which leads to the multiple branch structure in the I–V characteristics. On the basis of the numerical results we predict the I–V characteristics of the T ∗ -structure high-Tc cuprates.

We explore quantum phases in intrinsic Josephson junction (IJJ) stacks, whose in-plane area is so small that the capacitive coupling has a dominant role in the superconducting phase dynamics. In such cases, the effective Hamiltonian for the superconducting phase can be mapped onto that of one-dimensional ferromagnetically-interacting spin model, whose spin length S depends on the magnitude of the on-site Coulomb repulsion. The ferromagnetic model for IJJ’s prefers synchronized quantum features in contrast to the antiferromagnetically-interacting model in the conventional Josephson junction arrays.

Coherent microwave-induced effects in 2D arrays of hysteretic Josephson junctions placed in a perpendicular magnetic field are theoretically investigated. Two new phenomena: fractional inverse giant Josephson effect and modification of the V-A characteristic beyond Shapiro steps are found. A theory of these effects based on the idea of a moving vortex superlattice is developed. A new model of coherent phase dynamics is proposed.

Effect of electromagnetic environment on the phase dynamics of small Josephson junctions is studied in connection with the dissipation in supercurrent branch observed by Iansiti et al . It is found that the dissipation is determined by the tunnel resistance of quasi-particles excited above the superconducting gap by the high-frequency quantum fluctuations in electromagnetic fields. This offers a possible explanation of the temperature-independent dissipation observed experimentally.