Флуктуационное образование фазовых солитонов в двузонных сверхпроводящих мостиках

—Based on the Ginzburg–Landau theory, the dependence of the threshold energy δ F _thr of formation of a phase slip center from the current for a superconducting two-band bridge has been calculated. It has been found that, in the case of sufficiently long bridges and a weak interband Josephson coupling, there is a range of currents at which fluctuation transition from the state of the zero interband phase difference to the states with a phase soliton is possible, which manifests itself in a considerable decrease in the threshold energy δ F _thr, and a fluctuation change in the number of phase solitons in the bridge. In the case of a strong interband coupling, no fluctuation formation of phase solitons occurs and the dependence δ F _thr( I ) tends to the expression obtained earlier by Langer and Ambegaokar for a single-band superconductor.

Occupation-Constrained Interband dynamics of a Non-Hermitian Two-Band Bose–Hubbard Hamiltonian

The interband dynamics of a two-band Bose–Hubbard (BH) model is studied with strongly correlated bosons forming single-site double occupancies referred to as doublons. Our model for resonant doublon interband coupling exhibits interesting dynamical features such as quantum Zeno effect, the generation of states such as a two-band Bell-like state and an upper-band Mott-like state. The evolution of the asymptotic state is controlled here by the effective opening of one or both of the two bands, which models decay channels.

High temperature superconductivity in sulfur hydride under ultrahigh pressure: A complex superconducting phase beyond conventional BCS

The recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.