Radiation due to Josephson oscillations in layered superconductors

We derive the power of direct radiation into free space induced by Josephson oscillations in intrinsic Josephson junctions of layered superconductors. We consider the superradiation regime for a crystal cut in the form of a thin slice parallel to the c axis. We find that the radiation correction to the current-voltage characteristic in this regime depends only on crystal shape. We show that at a large number of junctions oscillations are synchronized providing high radiation power and efficiency in the terahertz frequency range. We discuss the crystal parameters and bias current optimal for radiation power and crystal cooling.     

The CDW transition with tripling of the period along the chains in quasi 1d crystals

It is shown that due to the influence of the interchain interaction the commensurate x3 CDW transition may be either I or II order. The possible types of 3d CDW ordering in this case are discussed. We point out also that for x3 transition the 2k_F and 4k_F anomalies coincide and add to increase the critical temperature and the gap or pseudogap. The results are discussed in connection with the properties of TTF-TCNQ under pressure.     

Nondemolition measurements of a single quantum spin using Josephson oscillations

We consider a single localized spin-1/2 between the singlet superconducting leads of a Josephson junction (e.g., a superconducting STM). For the spin subject to a dc magnetic field B parallel z, we study the spin dynamics and the possibility to measure the spin state via transport through the junction embedded in a dissipative circuit. Turning on the tunneling or a voltage bias induces oscillations of the Josephson current, with an amplitude sensitive to the initial value of the z component of the spin, S(z)=+/-1/2. At low temperatures, when effects of quasiparticles are negligible, this procedure realizes a quantum nondemolition measurement of S(z).     

On the theory of josephson coupling between layers in layered compounds

The amplitude of the Josephson current between superconducting layers and layer coupling are found to be decreased sharply with the increase of crystal structure disorder. In crystals intercalated with magnetic atoms or molecules the amplitude includes a component dependent on the state of localised spins and this component increases sharply when magnetic field is applied or ferromagnetic phase transition occurs.     

Percolation magnetoresistance in ferromagnetic superconductors

It is shown that the magnetoresistance (as a function of magnetic field H) in polycrystalline magnetic superconductors has the percolation character which is the consequence of the anisotropy of magnetic susceptibility. The magnetoresistance R_m(H), and the upper critical field H_c2(T) of ErRh₄B₄ are evaluated and compared with the experimental data.