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Register a new userExperimental Critical Current Patterns in Josephson Junction Ladders
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We present an experimental and theoretical study of the magnetic field dependence of the critical current of Josephson junction ladders. At variance with the well-known case of a one-dimensional (1D) parallel array of Josephson junctions the magnetic field patterns display a single minimum even for very low values of the self-inductance parameter $beta_{rm L}$. Experiments performed changing both the geometrical value of the inductance and the critical current of the junctions show a good agreement with numerical simulations. We argue that the observed magnetic field patterns are due to a peculiar mapping between the isotropic Josephson ladder and the 1D parallel array with the self-inductance parameter $beta_{rm L}^{rm eff}=beta_{rm L}+2$.
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Josephson junctions with an intrinsic phase shift of pi, so-called pi Josephson junctions, can be realized by a weak link of a d-wave superconductor with an appropriate boundary geometry. A model for the pairing potential of an according weak link is introduced which allows for the calculation of the influence of geometric parameters and temperature. From this model, current-phase relations and the critical current of the device are derived. The range of validity of the model is determined by comparison with selfconsistent solutions.
227 -
W. A. C. Passos
, U. R. de Oliveira
, W. A. Ortiz (Grupo den Supercondutividade e Magnetismo
2000
In this contribution we present a simple and effective procedure to determine the average critical current of a tridimensional disordered Josephson junction array (3D-DJJA). Using a contactless configuration we evaluate the average critical current and the typical width of the distribution through the analysis of the isothermal susceptibility response to the excitation field amplitude, chiAC(h). A 3D-DJJA fabricated from granular Nb is used to illustrate the method.
We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average Josephson phase psi=pm{phi}. The value of {phi} can be chosen by design in the interval 0<{phi}<pi. The junctions used in our experiments are fabricated as 0-{pi} Josephson junctions of moderate normalized length with asymmetric 0 and {pi} regions. We show that (a) these {phi} Josephson junctions have two critical currents, corresponding to the escape of the phase {psi} from -{phi} and +{phi} states; (b) the phase {psi} can be set to a particular state by tuning an external magnetic field or (c) by using a proper bias current sweep sequence. The experimental observations are in agreement with previous theoretical predictions.
104 -
W. A. C. Passos
, P. N. Lisboa-Filho
, W. A. Ortiz (Grupo den Supercondutividade e Magnetismo
2000
In this paper we determine the magnetic field dependence of the critical current of a tridimensional disordered Josephson junction array (3D-DJJA). A contactless configuration, employing measurements of the AC-susceptibility, is used to evaluate the average critical current of an array of YBa2Cu3O7-x. The critical field necessary to switch off supercurrents through the weak links at the working temperature is also obtained.
We compute the current voltage characteristic of a chain of identical Josephson circuits characterized by a large ratio of Josephson to charging energy that are envisioned as the implementation of topologically protected qubits. We show that in the limit of small coupling to the environment it exhibits a non-monotonous behavior with a maximum voltage followed by a parametrically large region where $Vpropto 1/I$. We argue that its experimental measurement provides a direct probe of the amplitude of the quantum transitions in constituting Josephson circuits and thus allows their full characterization.
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