Field dependence on the Josephson current and Fiske resonances in specially shaped Josephson junctions

Abstract

We investigated the magnetic-field dependence of the Josephson current and Fiske resonances in specially shaped Josephson junctions. In order to be able to use junctions for high-resolution X-ray spectroscopy, a very good suppression of the sidelobes of both the Josephson current and the Fiske resonances must be achieved.In a theoretical argument we show that a properly chosen junction shape leads to the sidelobe suppression of both the critical current and Fiske resonance amplitudes.The Josephson current and Fiske resonance amplitudes were measured as a function of the magnetic field, for junctions fabricated in Nb/AI technology. As expected, a very good sidelobe suppression was obtained for quartic-shaped junctions. For junctions with anodized structures within the tunneling area, the shape of the internal structures is reflected in the field dependence of both the Josephson current and the Fiske resonances. Finally, Fiske modes in these junctions have been imaged with low-temperature scanning electron microscopy, and we conclude that a quartic junction can be approximated by a rectangle, to describe the lower-order Fiske modes, whereas the high-order modes are specific to the exact shape of the junction.

Fabrication and photon detection experiments of Nb/Al and Ta/Al superconducting tunnel junctions

“…We made diamond-shaped STJs because diamond shape can efficiently suppress Josephson current by applying external magnetic field. (Gijsbertsen et al 1995). 5 The main four steps of the process are illustrated on Figure 1.…”

Fiske steps and Abrikosov vortices in Josephson tunnel junctions

“…For each value of B ⊥ the vortex density n A was calculated by using Eq. (12). The dependence of the maximum Josephson critical current I max c on the density of trapped Abrikosov vortices n A is shown in Fig.…”

“…In this case the Josephson critical current is strongly diminished but the magnitude of the Fiske step increases substantially. The magnetic field dependence of Fiske steps has been investigated in Josephson tunnel junctions with different shapes, namely, square shaped junction [10], circular shaped junction [11], quatric shaped junction [12]. In [13] the Fiske steps have been experimentally and theoretically investigated in the case of the annular shaped Josephson junction both in an external magnetic field and in a magnetic field generated by the injection current passed along one of the annular junction electrode.…”

Detection of single x-ray photons by an annular superconducting tunnel junction

“…Much effort has been devoted to finding the optimal STJ geometry to suppress I c by a weak parallel field. [3][4][5][6][7] The use of externally applied H ʈ has some drawbacks for detector application. First, the need for a continuously applied, stable field during detector operation could be problematic in some applications, for instance, in a satellite.…”